food chemistry
DESCRIPTION
Food Chemistry. IB Chemistry Option F. Nutrients. A food is any substance we deliberately ingest for nourishment, ideally containing one or more nutrients A nutrient is a component of food used by the body to provide energy or to grow and repair tissue Carbohydrates (sugars) - PowerPoint PPT PresentationTRANSCRIPT
Food Chemistry
IB Chemistry Option F
Nutrients A food is any substance we deliberately ingest
for nourishment ideally containing one or more nutrients
A nutrient is a component of food used by the body to provide energy or to grow and repair tissue
Carbohydrates (sugars) Lipids (fatsoils) Proteins Water Vitamins and minerals
Lack of nutrients leads to malnourishment
Food Groups 5 Main food groups
Grains ndash complex carbohydrates (polysaccharides) vitamins and minerals
Fruit ndash simple carbohydrates (mono and disaccharides) vitamins and minerals
Vegetables ndash simple and complex carbohydrates vitamins and minerals
MeatBeansFishPoultry ndash proteins vitamins and minerals fats and oils
Dairy ndash simple carbohydrates proteins fats and oils
Nutrients (carbohydrates)
Monosaccharides (ONE sugar) One carbonyl group (C=O) At least two hydroxyl groups (-OH) Empirical formula of CH2O
(carbo C and hydrate H2O) Ex Glucose C6H12O6 Ex Fructose C6H12O6
glucose
fructose
Nutrients (carbohydrates) Disaccharides (TWO
sugars) form when two monosaccharides come together releasing a water molecule (condensation reaction)
ldquoNew bondrdquo is called a glycosidic linkage between the two original monosaccharides
Polysaccharides (MANY sugars aka complex carbohydrates) are the combination of many simple sugars through glycosidic linkages
+ H2O
Nutrients (fats and oils)
Fats and oils are both classified as triglycerides Glycerol (CH2OHCHOHCH2OH) combines
with three fatty acid molecules (fatty = long nonpolar hydrocarbon chain and acid = carboxylic acid)
Also called triesters because of the formation of an ester group when an alcohol group (from glycerol) combines with a carboxylic acid group (from fatty acid)
Nutrients (fats and oils)
Formation of a triglyceride
Nutrients (proteins)
Proteins are polymers of amino acids 20 different amino acid ldquomonomersrdquo
form long chains of near infinite combinations
Typical protein is approximately 300 amino acids but can be made from less or more
Peptide bond (aka amide linkage) bonds amino acids together
+ H2O
Nutrients (water and vitaminsminerals)
Do not provide energy Water is used for transport and
various metabolic processes Vitamins and minerals are also
important in metabolic processes and as enzyme cofactors
Fats and Oils
Properties of a fat (chiefly melting point and chemical stability) are related to The degree of unsaturation ( of double bonds in
the hydrocarbon chains) More double bonds = lower melting point and more
reactive Length of the hydrocarbon chains
Shorter chains = lower melting point Whether the chain is cis or trans isomerized
around double bonds cis = lower melting point
Fats and Oils Saturated ndash all C-C single bonds
Fatty acid has a regular zig-zag shape due to geometry around sp3 hybridized carbon atoms
Monounsaturated ndash one C=C double bond Can be cis or trans isomerized
cis means hydrogen atoms are on same side of double bond trans means hydogen atoms are on opposite sides of the
double bond Polyunsaturated ndash multiple C=C double bonds
Can be either cis or trans isomerized A ldquofatrdquo is a tryglyceride that is solid at room
temperature Usually saturated monounsaturated or trans unsaturated
An oil is a triglyceride that is liquid at room temperature Usually polyunsaturated
Fats and Oils Fats with longer hydrocarbon chains are able to make
more van der Waals forces between each other making molecules harder to separate Higher melting point
Saturated fats have ldquostraightrdquo chains that pack closely and allow for lots of contact between molecules making molecules harder to separate Higher melting point
Trans-unsaturated fats have straight chains just as saturated fats do Higher melting point
Cis-unsaturated fats have irregularly-shaped less ldquostraightrdquo chains Do not pack as closely molecules are easier to separate Lower melting point
Fats and Oils
Fats and Oils ldquoDegree of Crystallizationrdquo is
related to the melting point of a fat Higher melting point means a higher
degree of crystallization (fat is more likely to be solid at room temperature)
Increases with Increasing degree of saturation Increasing amount of trans-unsaturation Higher molecular mass
Naturally-occuring triglycerides most commonly tend to be cis-unsaturated
Fats and Oils cis-unsaturated fats are typically the
healthiest Lower melting point allows for less
buildup of plaque in the arteries that can cause stroke or heart attack
trans-unsaturated fats are less healthy do not commonly occur naturally are harder to metabolize and buildup in fatty tissue Cause an increase in LDL cholesterol
(Low Density Lipoprotein or ldquobadrdquo cholesterol
Fats and Oils Unsaturated oils are more reactive due to the
possibility of addition reactions across the double bonds Are thus less stable and keep less well than saturated
fats Prone to auto-oxidation in the presence of light
(photo-oxidation) which is a reaction of the fats with atmospheric oxygen
Also more prone to hydrogenation (addition of hydrogen) hydrolysis (breaking of the fat back into glycerol and fatty acids) and microbial degradation
Fats and Oils Unsaturated fats are often artificially
hydrogenatedpartially hydrogenated Increases degree of saturation
Allows for control of texture because melting point is affected
Improves stability and shelf life as reactivity is decreased Improves cooking technique where more solid fats are
needed Hydrogen gas is added over a solid nickel catalyst
Double bonds converted to single bonds and degree of saturation increases
Drawback - decreases the health value as fats are healthier when mono- or poly-unsaturated
Ni(s)
Shelf Life Foods gradually become unfit for consumption
due to Spoilage (growth of organisms) Changes in texture smell flavor or appearance
Undesirable processes caused by Change in water content Chemical reactions Exposure to light Changes in temperature
Shelf life is the length of time a product can be stored without these undesirable changes occurring
Shelf Life Change in water content
Causes texture change Loss of water increases exposure to air and thus oxidation
Causes rancidity and discoloration Increase in water encourages microbial growth and
spoilage Chemical reactionstemperature change
Increased temperature increases rates of ldquoharmful reactionsrdquo
Changes in pH or temperature affect the amount of water in a food
Souring with decrease in pH Changes color Can decrease nutritional value
Light provides energy for ldquoharmfulrdquo chemical reactions
Shelf Life Rancidity is a common type of food
degradation Unpleasant textures smells and flavors of fats
and oils
Two types of rancidity Hydrolytic rancidity ndash ester bond in fat is broken
yielding free fatty acids (reverse of formation of a fat) Oxidative rancidity ndash oxygen reacts near the C=C
double bonds in unsaturated fats
Shelf Life Hydrolytic rancidity of fats and oils
reverse of fat formation uses water (hydro lysis = ldquowaterrdquo ldquosplittingrdquo) to split triglycerides back into glycerol and fatty acids
Encouraged by Lipase ndash an enzyme produced by microorganisms Deep frying ndash encourages reaction of fats with moisture in
food Releases free fatty acids
4 ndash 8 carbon fatty acids have a powerfully pungent aromaflavor
palmitic stearic oleic lauric acids give a soapy fatty feel to foods
Shelf Life Oxidative rancidity of fats and oils
Reaction of atmospheric oxygen with fats and oils initiates complex process producing highly reactive free radicals
Products include unpleasant smellingtasting byproducts
More of an issue with increasing degree of unsaturation (more C=C double bonds to react with)
Encouraged by the presence of light (photo-oxidation) Enzymes produced by microorganisms
Shelf Life Oxidative rancidity of fats and oils occurs in 3
steps Initiation by exposure to light ndash produces highly
reactive hydrocarbon radicals (species with an unpaired electron)
R-H R + H Propagation ndash radicals produce other radicals
R + O2 R-O-O ROO + R-H R-O-O-H + R
Termination ndash radicals encounter one another and end the reaction
R + R R-R R-O-O + R-O-O R-O-O-O-O-R R + R-O-O R-O-O-R
(R-H = unsaturated fat or oil R = hydrocarbon radical images on next slide)
Shelf Life Initiation
Shelf Life Propagation
Shelf Life Termination
Shelf Life Shelf life is prolonged by hindering spoilage
processes Packaging
Opaque or darkened packages block light Can be gas impermeable to limit exposure to oxygen and water Can be filled with inert gases or vacuum packed (no gases)
Storage Low temperatures slow harmful reactions Smoking or drying foods removes water and hinder microbial
growth Additives
Salt or sugar added to remove water and hinder microbial growth
KNO3 or NaNO3 salts are reducing agents and can prevent harmful oxidation reactions
Anti-microbial agents Pickling - Organic acids and their salts (ex benzoic acid and
benzoate salts) make pH unfavorable for microbial growth Fermentation ndash production of alcohol hinders microbial growth
Shelf Life Antioxidants delay oxidative degradation
processes by reacting with oxygen to contain free radical formation Can occur naturally
Vitamin C (ascorbic acid) ndash citrus and green vegetables Vitamin E (tocopherol) ndash nuts seeds grains canola oil Beta-carotene ndash carrots broccoli tomatoes peaches Selenium ndash shellfish meat eggs grains Foods high in natural antioxidants green tea blueberries
cranberries dark chocolate turmeric oregano Can be synthetic additives but may have harmful
side effects BHA BHT PG THBP TBHQ
these are all based around a phenol
groupwhich is not
necessarily found in natural
antioxidants
(Full structures in
data booklet)
Shelf Life Types of antioxidants
Free radical quenchers React with radicals to produce less reactive radicals (HA =
quencher)R-O-O + HA R-O-O-H + A
Chelating agents Form very stable complex ions with transition metals (which
can produce radicals) Found naturally in rosemary tea and mustard Salts of the organic acid EDTA are added as artificial chelating
agents Reducing agents
React with oxygen or hydroperoxides Vitamin C or carotenoids are natural reducing agents
Color Foods are colored by either pigments or dyes
Pigments occur naturally Dyes are added artificially and must be tested for
safety Dyes or pigments will absorb a range of light
frequencies and reflect others The color we see in a dye or pigment is the result of
the colors of light reflected not absorbed Ex chlorophyll in green leaf vegetables absorbs red
and blue light reflecting green Molecular structures all involve extensive
delocalized pi bonding (shown on next slide) This system of delocalized pi bonding (conjugated
system) is responsible for the color we see
Color Some of the most common natural pigment
groups are Anthocyanins
Ex Cyanidin Carotenoids
Ex Beta-carotene Chlorophyll
Ex Chlorophyll-A Heme
Ex Heme B group
heme B groupchlorophyll-A
cyanidin
β-carotene
Color Anthocyanins
Responsible for reds pinks blues in berries beets flowers (Flavonones which give color to red grapes and berries are closely related to anthocyanins)
3-ring structures with varying numbers of OH groups in varying positions
Structure and therefore color is related to pH
predominantly red at low pH (acidic) blue at high pH (basic) and colorlesspale yellow at neutral pH
Temperature May break down at high temperatures and cause browning
Exposure to metal Form complexes with iron and aluminum and can change color
Color also affected when anthocyanins bond to sugars
Color Color of anthocyanins is pH dependent (they are
acidbase indicators)
Color Carotenes
Responsible for orange yellow and red colors in foods like carrots bananas tomatoes and saffron
Characterized by long hydrocarbon chains that often have carbon rings on the ends
Have nutritional value precursors to vitamin A (important in vision) act as antioxidants
Relatively stable during food processing but presence of C=C double bonds in hydrocarbon chain opens them up to oxidative degradation as seen in fats
Causes discoloration Prevents carotenoids from being able to be converted to
vitamin A
Color
β-carotene
Color Astaxanthin is a red pigment similar to
carotenoids found in lobster crab and salmon Bonds to proteins in the live animal and gives a
bluegreen color When heated bond to protein is broken which modifies
the structure and frequency of light absorbed appears bright red
Also an antioxidant
Color Chlorophyll
Green pigment responsible for plant photosynthesis Found in green vegetables Structure is centered around a porphyrin ring ndash a
planar ring system with 4 nitrogen atoms surrounding a central metal atom (magnesium in the case of chlorophyll)
Two forms chlorophyll A and chlorophyll B In chlorophyll B an aldehyde side chain replaces a
methyl side chain When cooked plant cells release acids
Causes an H+ ion to replace magnesium atom in center of structure causing a color change to an olivebrown
Opens the possibility for photodegradation (breakdown by light)
Color
chlorophyll A
(replaced with an aldehyde in chlorophyll B)
Color Heme
Pigment found in red blood cells Structure is similar to chlorophyll but there is an iron
atom in the center of the porphyrin ring Found in the protein myoglobin responsible for
oxygen transport Bright red when bound to oxygen but slow process
of autoxidation converts iron from +2 to +3 changing color to brown (less desirable) (myoglobin metmyoglobin)
Color change can be prevented by vacuum packing or packing with an inert gas like CO2
Color
heme groupin myoglobin
Color Color in foods is a result of the structures seen in
anthocyanins carotenoids chlorophylls and hemes All of these structures include an extensive network of
delocalized pi-bonds Alternating single and double bonds is called a conjugated
system The greater the extent of pi bond delocalization the closer
together in energy bonding and antibonding orbitals become All molecules absorb light energy as it promotes e-s between
molecular orbitals (bonding and antibonding orbitals) ndash energy required is proportional to distance between orbitals (less distance = less energy)
As orbitals are close together in a conjugated system low energy light (in the visible region) is absorbed for e- promotion
Color in these groups is the product of visible light absorption - color we see is complementary to the color(s) absorbed
Molecules without an extensive delocalized pi bond network (conjugated system) lack color as orbitals are further apart and only higher energy light promotes e-s (ex the anthocyanin carbinol)
Color Some pigments are water soluble because the
structures contain a large amount of -OH groups (H-bonding) Anthocyanins
Some pigments are fat soluble (ie not water soluble) because their structures contain little or no -OH groups (no H-bonding) carotenoids
Color
Many synthetic dyes are biochemically active and could be potentially harmful
Short-term toxicity easy to test and categorize but long-term effects are more difficult to study
Use of dyes in foods must be regulated but regulations are not standardized internationally posing issues in trade
Color Cooking foods often leads to browning
Two processes responsible Maillard reactions ndash combination of sugars and
proteins Caramelization ndash dehydration of sugar
Both involve removal of water molecule(s)
Color Maillard reactions
Sugars and proteins within the food combine in a condensation reaction
Aldehyde group in sugar (O atom) combines with amino group in protein (2 H atoms)
Initial condensation products polymerize to form brown-colored melanoidins
Maillard reactions only happen gt 140deg C Rate depends on amino acid present (ex lysine
reacts faster than cysteine)
initialcondensationproduct
Color Caramelization
Happens in foods high in carbohydrates Sugars dehydrate (lose H2O) at high temperatures
leaving behind C (dark brown color)
Browning intensifies the longer food is cooked eventually burning it (pure carbon is black)
Rate depends on Sugar type (fructose in fruits caramelizes very quickly) pH ndash extremes (high and low) promote caramelization
Genetically Modified Foods
Produced when organisms with modified DNA are used in food production Used to
Provide pest or disease resistance Bt corn contains toxin from bacillis thuringiensis that kills
insect pests Fungal-resistant potatoes Nematode-resistant bananas (nematode = worm)
Improve quality and range of crop Development of higher-yielding rice varieties Development of corn that can grow in dryer environments
Produce medicines or other products in large quantities Use of chickens that have been modified to lay eggs
containing human interferon (combats tumors and viruses) Use of cows to produce milk rich in omega-3 fatty acids
(polyunsaturated fats essential to growth development brain function)
Moth larva
Genetically Modified Foods
Drawbacks Are GM foods safe Will GM food production alter the natural ecosystem Do we understand enough about genetic
modification GM foods
Can cause allergic reactions in some people Have a slightly different composition from natural foods ndash
alters diet Produce altered pollen ndash might escape and cross with natural
species Long-term effects might be catastrophic unknown so far
Texture Food texture is related to physical properties
Hardness Elasticity Viscosity
These properties can be altered by Cooking Use of dispersed systems
Dispersed system = a stabilized macroscopically homogeneous mixture of two immiscible phases
(this means two substances that would not ordinarily mix ldquoappear tordquo on a macroscopic level (although at the molecular level they are still separate)
Texture Many types of dispersed systems name depends on
the physical states of the substances mixed LiquidSolid or SolidLiquid
Solid particles suspended in a liquid is called a suspension
Ex Blood (blood cells suspended in plasma) Liquid dispersed throughout a solid medium is called a
gel Ex Fruit Jelly (water trapped in a solid protein matrix)
LiquidLiquid Stable blend of two liquids that donrsquot mix is called an
emulsion Ex Mayonaisse (oil droplets suspended in aqueous system)
LiquidGas or GasLiquid Gas bubbles trapped in liquid medium is called a foam
Ex Whipped cream or egg whites Liquid droplets suspended in gas are called aerosols
Ex Aromas from food carried through the air
Texture Dispersed systems will slowly separate over
time Separation can be slowed by adding emulsifiers
Emulsifiers are stabilizers used to keep immiscible substance together
Have surfactant capability (can bind to both substances in suspension)
Similar to micelles in the action of soaps
Ex Lecithin Found commonly in egg
yolks One end is highly charged
and water soluble (bonds toaqueous phase) the otheris not (bonds to non-aqueous phase)
Texture Lecithin in mayonnaise
Lecithin is the emulsifier Mayonnaise made by beating eggs with
vinegar and oil Lecithin is found in eggs ndash charged
hydrophilic end bonds well to vinegar uncharged hydrophobic end bonds to oil
Vigorous beating produces many small oil droplets maximizing surface area for lecithin to act on and produce a stable emulsion
Stabilizers like sodium phosphate or metals are added to prevent separation (chefs use metal bowls)
hydrophilic
hydrophobic
Stereochemistry in Food Many food-specific compounds have a chiral
carbon atom and thus exist as two different enantiomers (optical isomers) Optical isomers are mirror images of one another ldquoOptical activityrdquo refers to the fact that the two mirror
image isomers rotate the direction of plane-polarized light in opposite directions
Enantiomers that rotate polarized light in a clockwise direction are said to be dextrorotatory (dex-tro-rota-tory) and have a + rotational value (d +) ndash In Latin dexter means ldquoright siderdquo
Enantiomers that rotate polarized light in an anti-clockwise direction are said to be laevorotatory (lay-vo-rota-tory) and have a ndash rotational value (l -) ndash In Latin laevus means ldquoleft siderdquo
There are two systems used to provide specific names to each enantiomeric form
Stereochemistry in Food Older system used for naming sugars and amino
acids Enantiomeric forms are labeled ldquoLrdquo and ldquoDrdquo
Again Laevus for left and Dexter for right Based off a compound called glyceraldehyde
chiral carbon
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Nutrients A food is any substance we deliberately ingest
for nourishment ideally containing one or more nutrients
A nutrient is a component of food used by the body to provide energy or to grow and repair tissue
Carbohydrates (sugars) Lipids (fatsoils) Proteins Water Vitamins and minerals
Lack of nutrients leads to malnourishment
Food Groups 5 Main food groups
Grains ndash complex carbohydrates (polysaccharides) vitamins and minerals
Fruit ndash simple carbohydrates (mono and disaccharides) vitamins and minerals
Vegetables ndash simple and complex carbohydrates vitamins and minerals
MeatBeansFishPoultry ndash proteins vitamins and minerals fats and oils
Dairy ndash simple carbohydrates proteins fats and oils
Nutrients (carbohydrates)
Monosaccharides (ONE sugar) One carbonyl group (C=O) At least two hydroxyl groups (-OH) Empirical formula of CH2O
(carbo C and hydrate H2O) Ex Glucose C6H12O6 Ex Fructose C6H12O6
glucose
fructose
Nutrients (carbohydrates) Disaccharides (TWO
sugars) form when two monosaccharides come together releasing a water molecule (condensation reaction)
ldquoNew bondrdquo is called a glycosidic linkage between the two original monosaccharides
Polysaccharides (MANY sugars aka complex carbohydrates) are the combination of many simple sugars through glycosidic linkages
+ H2O
Nutrients (fats and oils)
Fats and oils are both classified as triglycerides Glycerol (CH2OHCHOHCH2OH) combines
with three fatty acid molecules (fatty = long nonpolar hydrocarbon chain and acid = carboxylic acid)
Also called triesters because of the formation of an ester group when an alcohol group (from glycerol) combines with a carboxylic acid group (from fatty acid)
Nutrients (fats and oils)
Formation of a triglyceride
Nutrients (proteins)
Proteins are polymers of amino acids 20 different amino acid ldquomonomersrdquo
form long chains of near infinite combinations
Typical protein is approximately 300 amino acids but can be made from less or more
Peptide bond (aka amide linkage) bonds amino acids together
+ H2O
Nutrients (water and vitaminsminerals)
Do not provide energy Water is used for transport and
various metabolic processes Vitamins and minerals are also
important in metabolic processes and as enzyme cofactors
Fats and Oils
Properties of a fat (chiefly melting point and chemical stability) are related to The degree of unsaturation ( of double bonds in
the hydrocarbon chains) More double bonds = lower melting point and more
reactive Length of the hydrocarbon chains
Shorter chains = lower melting point Whether the chain is cis or trans isomerized
around double bonds cis = lower melting point
Fats and Oils Saturated ndash all C-C single bonds
Fatty acid has a regular zig-zag shape due to geometry around sp3 hybridized carbon atoms
Monounsaturated ndash one C=C double bond Can be cis or trans isomerized
cis means hydrogen atoms are on same side of double bond trans means hydogen atoms are on opposite sides of the
double bond Polyunsaturated ndash multiple C=C double bonds
Can be either cis or trans isomerized A ldquofatrdquo is a tryglyceride that is solid at room
temperature Usually saturated monounsaturated or trans unsaturated
An oil is a triglyceride that is liquid at room temperature Usually polyunsaturated
Fats and Oils Fats with longer hydrocarbon chains are able to make
more van der Waals forces between each other making molecules harder to separate Higher melting point
Saturated fats have ldquostraightrdquo chains that pack closely and allow for lots of contact between molecules making molecules harder to separate Higher melting point
Trans-unsaturated fats have straight chains just as saturated fats do Higher melting point
Cis-unsaturated fats have irregularly-shaped less ldquostraightrdquo chains Do not pack as closely molecules are easier to separate Lower melting point
Fats and Oils
Fats and Oils ldquoDegree of Crystallizationrdquo is
related to the melting point of a fat Higher melting point means a higher
degree of crystallization (fat is more likely to be solid at room temperature)
Increases with Increasing degree of saturation Increasing amount of trans-unsaturation Higher molecular mass
Naturally-occuring triglycerides most commonly tend to be cis-unsaturated
Fats and Oils cis-unsaturated fats are typically the
healthiest Lower melting point allows for less
buildup of plaque in the arteries that can cause stroke or heart attack
trans-unsaturated fats are less healthy do not commonly occur naturally are harder to metabolize and buildup in fatty tissue Cause an increase in LDL cholesterol
(Low Density Lipoprotein or ldquobadrdquo cholesterol
Fats and Oils Unsaturated oils are more reactive due to the
possibility of addition reactions across the double bonds Are thus less stable and keep less well than saturated
fats Prone to auto-oxidation in the presence of light
(photo-oxidation) which is a reaction of the fats with atmospheric oxygen
Also more prone to hydrogenation (addition of hydrogen) hydrolysis (breaking of the fat back into glycerol and fatty acids) and microbial degradation
Fats and Oils Unsaturated fats are often artificially
hydrogenatedpartially hydrogenated Increases degree of saturation
Allows for control of texture because melting point is affected
Improves stability and shelf life as reactivity is decreased Improves cooking technique where more solid fats are
needed Hydrogen gas is added over a solid nickel catalyst
Double bonds converted to single bonds and degree of saturation increases
Drawback - decreases the health value as fats are healthier when mono- or poly-unsaturated
Ni(s)
Shelf Life Foods gradually become unfit for consumption
due to Spoilage (growth of organisms) Changes in texture smell flavor or appearance
Undesirable processes caused by Change in water content Chemical reactions Exposure to light Changes in temperature
Shelf life is the length of time a product can be stored without these undesirable changes occurring
Shelf Life Change in water content
Causes texture change Loss of water increases exposure to air and thus oxidation
Causes rancidity and discoloration Increase in water encourages microbial growth and
spoilage Chemical reactionstemperature change
Increased temperature increases rates of ldquoharmful reactionsrdquo
Changes in pH or temperature affect the amount of water in a food
Souring with decrease in pH Changes color Can decrease nutritional value
Light provides energy for ldquoharmfulrdquo chemical reactions
Shelf Life Rancidity is a common type of food
degradation Unpleasant textures smells and flavors of fats
and oils
Two types of rancidity Hydrolytic rancidity ndash ester bond in fat is broken
yielding free fatty acids (reverse of formation of a fat) Oxidative rancidity ndash oxygen reacts near the C=C
double bonds in unsaturated fats
Shelf Life Hydrolytic rancidity of fats and oils
reverse of fat formation uses water (hydro lysis = ldquowaterrdquo ldquosplittingrdquo) to split triglycerides back into glycerol and fatty acids
Encouraged by Lipase ndash an enzyme produced by microorganisms Deep frying ndash encourages reaction of fats with moisture in
food Releases free fatty acids
4 ndash 8 carbon fatty acids have a powerfully pungent aromaflavor
palmitic stearic oleic lauric acids give a soapy fatty feel to foods
Shelf Life Oxidative rancidity of fats and oils
Reaction of atmospheric oxygen with fats and oils initiates complex process producing highly reactive free radicals
Products include unpleasant smellingtasting byproducts
More of an issue with increasing degree of unsaturation (more C=C double bonds to react with)
Encouraged by the presence of light (photo-oxidation) Enzymes produced by microorganisms
Shelf Life Oxidative rancidity of fats and oils occurs in 3
steps Initiation by exposure to light ndash produces highly
reactive hydrocarbon radicals (species with an unpaired electron)
R-H R + H Propagation ndash radicals produce other radicals
R + O2 R-O-O ROO + R-H R-O-O-H + R
Termination ndash radicals encounter one another and end the reaction
R + R R-R R-O-O + R-O-O R-O-O-O-O-R R + R-O-O R-O-O-R
(R-H = unsaturated fat or oil R = hydrocarbon radical images on next slide)
Shelf Life Initiation
Shelf Life Propagation
Shelf Life Termination
Shelf Life Shelf life is prolonged by hindering spoilage
processes Packaging
Opaque or darkened packages block light Can be gas impermeable to limit exposure to oxygen and water Can be filled with inert gases or vacuum packed (no gases)
Storage Low temperatures slow harmful reactions Smoking or drying foods removes water and hinder microbial
growth Additives
Salt or sugar added to remove water and hinder microbial growth
KNO3 or NaNO3 salts are reducing agents and can prevent harmful oxidation reactions
Anti-microbial agents Pickling - Organic acids and their salts (ex benzoic acid and
benzoate salts) make pH unfavorable for microbial growth Fermentation ndash production of alcohol hinders microbial growth
Shelf Life Antioxidants delay oxidative degradation
processes by reacting with oxygen to contain free radical formation Can occur naturally
Vitamin C (ascorbic acid) ndash citrus and green vegetables Vitamin E (tocopherol) ndash nuts seeds grains canola oil Beta-carotene ndash carrots broccoli tomatoes peaches Selenium ndash shellfish meat eggs grains Foods high in natural antioxidants green tea blueberries
cranberries dark chocolate turmeric oregano Can be synthetic additives but may have harmful
side effects BHA BHT PG THBP TBHQ
these are all based around a phenol
groupwhich is not
necessarily found in natural
antioxidants
(Full structures in
data booklet)
Shelf Life Types of antioxidants
Free radical quenchers React with radicals to produce less reactive radicals (HA =
quencher)R-O-O + HA R-O-O-H + A
Chelating agents Form very stable complex ions with transition metals (which
can produce radicals) Found naturally in rosemary tea and mustard Salts of the organic acid EDTA are added as artificial chelating
agents Reducing agents
React with oxygen or hydroperoxides Vitamin C or carotenoids are natural reducing agents
Color Foods are colored by either pigments or dyes
Pigments occur naturally Dyes are added artificially and must be tested for
safety Dyes or pigments will absorb a range of light
frequencies and reflect others The color we see in a dye or pigment is the result of
the colors of light reflected not absorbed Ex chlorophyll in green leaf vegetables absorbs red
and blue light reflecting green Molecular structures all involve extensive
delocalized pi bonding (shown on next slide) This system of delocalized pi bonding (conjugated
system) is responsible for the color we see
Color Some of the most common natural pigment
groups are Anthocyanins
Ex Cyanidin Carotenoids
Ex Beta-carotene Chlorophyll
Ex Chlorophyll-A Heme
Ex Heme B group
heme B groupchlorophyll-A
cyanidin
β-carotene
Color Anthocyanins
Responsible for reds pinks blues in berries beets flowers (Flavonones which give color to red grapes and berries are closely related to anthocyanins)
3-ring structures with varying numbers of OH groups in varying positions
Structure and therefore color is related to pH
predominantly red at low pH (acidic) blue at high pH (basic) and colorlesspale yellow at neutral pH
Temperature May break down at high temperatures and cause browning
Exposure to metal Form complexes with iron and aluminum and can change color
Color also affected when anthocyanins bond to sugars
Color Color of anthocyanins is pH dependent (they are
acidbase indicators)
Color Carotenes
Responsible for orange yellow and red colors in foods like carrots bananas tomatoes and saffron
Characterized by long hydrocarbon chains that often have carbon rings on the ends
Have nutritional value precursors to vitamin A (important in vision) act as antioxidants
Relatively stable during food processing but presence of C=C double bonds in hydrocarbon chain opens them up to oxidative degradation as seen in fats
Causes discoloration Prevents carotenoids from being able to be converted to
vitamin A
Color
β-carotene
Color Astaxanthin is a red pigment similar to
carotenoids found in lobster crab and salmon Bonds to proteins in the live animal and gives a
bluegreen color When heated bond to protein is broken which modifies
the structure and frequency of light absorbed appears bright red
Also an antioxidant
Color Chlorophyll
Green pigment responsible for plant photosynthesis Found in green vegetables Structure is centered around a porphyrin ring ndash a
planar ring system with 4 nitrogen atoms surrounding a central metal atom (magnesium in the case of chlorophyll)
Two forms chlorophyll A and chlorophyll B In chlorophyll B an aldehyde side chain replaces a
methyl side chain When cooked plant cells release acids
Causes an H+ ion to replace magnesium atom in center of structure causing a color change to an olivebrown
Opens the possibility for photodegradation (breakdown by light)
Color
chlorophyll A
(replaced with an aldehyde in chlorophyll B)
Color Heme
Pigment found in red blood cells Structure is similar to chlorophyll but there is an iron
atom in the center of the porphyrin ring Found in the protein myoglobin responsible for
oxygen transport Bright red when bound to oxygen but slow process
of autoxidation converts iron from +2 to +3 changing color to brown (less desirable) (myoglobin metmyoglobin)
Color change can be prevented by vacuum packing or packing with an inert gas like CO2
Color
heme groupin myoglobin
Color Color in foods is a result of the structures seen in
anthocyanins carotenoids chlorophylls and hemes All of these structures include an extensive network of
delocalized pi-bonds Alternating single and double bonds is called a conjugated
system The greater the extent of pi bond delocalization the closer
together in energy bonding and antibonding orbitals become All molecules absorb light energy as it promotes e-s between
molecular orbitals (bonding and antibonding orbitals) ndash energy required is proportional to distance between orbitals (less distance = less energy)
As orbitals are close together in a conjugated system low energy light (in the visible region) is absorbed for e- promotion
Color in these groups is the product of visible light absorption - color we see is complementary to the color(s) absorbed
Molecules without an extensive delocalized pi bond network (conjugated system) lack color as orbitals are further apart and only higher energy light promotes e-s (ex the anthocyanin carbinol)
Color Some pigments are water soluble because the
structures contain a large amount of -OH groups (H-bonding) Anthocyanins
Some pigments are fat soluble (ie not water soluble) because their structures contain little or no -OH groups (no H-bonding) carotenoids
Color
Many synthetic dyes are biochemically active and could be potentially harmful
Short-term toxicity easy to test and categorize but long-term effects are more difficult to study
Use of dyes in foods must be regulated but regulations are not standardized internationally posing issues in trade
Color Cooking foods often leads to browning
Two processes responsible Maillard reactions ndash combination of sugars and
proteins Caramelization ndash dehydration of sugar
Both involve removal of water molecule(s)
Color Maillard reactions
Sugars and proteins within the food combine in a condensation reaction
Aldehyde group in sugar (O atom) combines with amino group in protein (2 H atoms)
Initial condensation products polymerize to form brown-colored melanoidins
Maillard reactions only happen gt 140deg C Rate depends on amino acid present (ex lysine
reacts faster than cysteine)
initialcondensationproduct
Color Caramelization
Happens in foods high in carbohydrates Sugars dehydrate (lose H2O) at high temperatures
leaving behind C (dark brown color)
Browning intensifies the longer food is cooked eventually burning it (pure carbon is black)
Rate depends on Sugar type (fructose in fruits caramelizes very quickly) pH ndash extremes (high and low) promote caramelization
Genetically Modified Foods
Produced when organisms with modified DNA are used in food production Used to
Provide pest or disease resistance Bt corn contains toxin from bacillis thuringiensis that kills
insect pests Fungal-resistant potatoes Nematode-resistant bananas (nematode = worm)
Improve quality and range of crop Development of higher-yielding rice varieties Development of corn that can grow in dryer environments
Produce medicines or other products in large quantities Use of chickens that have been modified to lay eggs
containing human interferon (combats tumors and viruses) Use of cows to produce milk rich in omega-3 fatty acids
(polyunsaturated fats essential to growth development brain function)
Moth larva
Genetically Modified Foods
Drawbacks Are GM foods safe Will GM food production alter the natural ecosystem Do we understand enough about genetic
modification GM foods
Can cause allergic reactions in some people Have a slightly different composition from natural foods ndash
alters diet Produce altered pollen ndash might escape and cross with natural
species Long-term effects might be catastrophic unknown so far
Texture Food texture is related to physical properties
Hardness Elasticity Viscosity
These properties can be altered by Cooking Use of dispersed systems
Dispersed system = a stabilized macroscopically homogeneous mixture of two immiscible phases
(this means two substances that would not ordinarily mix ldquoappear tordquo on a macroscopic level (although at the molecular level they are still separate)
Texture Many types of dispersed systems name depends on
the physical states of the substances mixed LiquidSolid or SolidLiquid
Solid particles suspended in a liquid is called a suspension
Ex Blood (blood cells suspended in plasma) Liquid dispersed throughout a solid medium is called a
gel Ex Fruit Jelly (water trapped in a solid protein matrix)
LiquidLiquid Stable blend of two liquids that donrsquot mix is called an
emulsion Ex Mayonaisse (oil droplets suspended in aqueous system)
LiquidGas or GasLiquid Gas bubbles trapped in liquid medium is called a foam
Ex Whipped cream or egg whites Liquid droplets suspended in gas are called aerosols
Ex Aromas from food carried through the air
Texture Dispersed systems will slowly separate over
time Separation can be slowed by adding emulsifiers
Emulsifiers are stabilizers used to keep immiscible substance together
Have surfactant capability (can bind to both substances in suspension)
Similar to micelles in the action of soaps
Ex Lecithin Found commonly in egg
yolks One end is highly charged
and water soluble (bonds toaqueous phase) the otheris not (bonds to non-aqueous phase)
Texture Lecithin in mayonnaise
Lecithin is the emulsifier Mayonnaise made by beating eggs with
vinegar and oil Lecithin is found in eggs ndash charged
hydrophilic end bonds well to vinegar uncharged hydrophobic end bonds to oil
Vigorous beating produces many small oil droplets maximizing surface area for lecithin to act on and produce a stable emulsion
Stabilizers like sodium phosphate or metals are added to prevent separation (chefs use metal bowls)
hydrophilic
hydrophobic
Stereochemistry in Food Many food-specific compounds have a chiral
carbon atom and thus exist as two different enantiomers (optical isomers) Optical isomers are mirror images of one another ldquoOptical activityrdquo refers to the fact that the two mirror
image isomers rotate the direction of plane-polarized light in opposite directions
Enantiomers that rotate polarized light in a clockwise direction are said to be dextrorotatory (dex-tro-rota-tory) and have a + rotational value (d +) ndash In Latin dexter means ldquoright siderdquo
Enantiomers that rotate polarized light in an anti-clockwise direction are said to be laevorotatory (lay-vo-rota-tory) and have a ndash rotational value (l -) ndash In Latin laevus means ldquoleft siderdquo
There are two systems used to provide specific names to each enantiomeric form
Stereochemistry in Food Older system used for naming sugars and amino
acids Enantiomeric forms are labeled ldquoLrdquo and ldquoDrdquo
Again Laevus for left and Dexter for right Based off a compound called glyceraldehyde
chiral carbon
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Food Groups 5 Main food groups
Grains ndash complex carbohydrates (polysaccharides) vitamins and minerals
Fruit ndash simple carbohydrates (mono and disaccharides) vitamins and minerals
Vegetables ndash simple and complex carbohydrates vitamins and minerals
MeatBeansFishPoultry ndash proteins vitamins and minerals fats and oils
Dairy ndash simple carbohydrates proteins fats and oils
Nutrients (carbohydrates)
Monosaccharides (ONE sugar) One carbonyl group (C=O) At least two hydroxyl groups (-OH) Empirical formula of CH2O
(carbo C and hydrate H2O) Ex Glucose C6H12O6 Ex Fructose C6H12O6
glucose
fructose
Nutrients (carbohydrates) Disaccharides (TWO
sugars) form when two monosaccharides come together releasing a water molecule (condensation reaction)
ldquoNew bondrdquo is called a glycosidic linkage between the two original monosaccharides
Polysaccharides (MANY sugars aka complex carbohydrates) are the combination of many simple sugars through glycosidic linkages
+ H2O
Nutrients (fats and oils)
Fats and oils are both classified as triglycerides Glycerol (CH2OHCHOHCH2OH) combines
with three fatty acid molecules (fatty = long nonpolar hydrocarbon chain and acid = carboxylic acid)
Also called triesters because of the formation of an ester group when an alcohol group (from glycerol) combines with a carboxylic acid group (from fatty acid)
Nutrients (fats and oils)
Formation of a triglyceride
Nutrients (proteins)
Proteins are polymers of amino acids 20 different amino acid ldquomonomersrdquo
form long chains of near infinite combinations
Typical protein is approximately 300 amino acids but can be made from less or more
Peptide bond (aka amide linkage) bonds amino acids together
+ H2O
Nutrients (water and vitaminsminerals)
Do not provide energy Water is used for transport and
various metabolic processes Vitamins and minerals are also
important in metabolic processes and as enzyme cofactors
Fats and Oils
Properties of a fat (chiefly melting point and chemical stability) are related to The degree of unsaturation ( of double bonds in
the hydrocarbon chains) More double bonds = lower melting point and more
reactive Length of the hydrocarbon chains
Shorter chains = lower melting point Whether the chain is cis or trans isomerized
around double bonds cis = lower melting point
Fats and Oils Saturated ndash all C-C single bonds
Fatty acid has a regular zig-zag shape due to geometry around sp3 hybridized carbon atoms
Monounsaturated ndash one C=C double bond Can be cis or trans isomerized
cis means hydrogen atoms are on same side of double bond trans means hydogen atoms are on opposite sides of the
double bond Polyunsaturated ndash multiple C=C double bonds
Can be either cis or trans isomerized A ldquofatrdquo is a tryglyceride that is solid at room
temperature Usually saturated monounsaturated or trans unsaturated
An oil is a triglyceride that is liquid at room temperature Usually polyunsaturated
Fats and Oils Fats with longer hydrocarbon chains are able to make
more van der Waals forces between each other making molecules harder to separate Higher melting point
Saturated fats have ldquostraightrdquo chains that pack closely and allow for lots of contact between molecules making molecules harder to separate Higher melting point
Trans-unsaturated fats have straight chains just as saturated fats do Higher melting point
Cis-unsaturated fats have irregularly-shaped less ldquostraightrdquo chains Do not pack as closely molecules are easier to separate Lower melting point
Fats and Oils
Fats and Oils ldquoDegree of Crystallizationrdquo is
related to the melting point of a fat Higher melting point means a higher
degree of crystallization (fat is more likely to be solid at room temperature)
Increases with Increasing degree of saturation Increasing amount of trans-unsaturation Higher molecular mass
Naturally-occuring triglycerides most commonly tend to be cis-unsaturated
Fats and Oils cis-unsaturated fats are typically the
healthiest Lower melting point allows for less
buildup of plaque in the arteries that can cause stroke or heart attack
trans-unsaturated fats are less healthy do not commonly occur naturally are harder to metabolize and buildup in fatty tissue Cause an increase in LDL cholesterol
(Low Density Lipoprotein or ldquobadrdquo cholesterol
Fats and Oils Unsaturated oils are more reactive due to the
possibility of addition reactions across the double bonds Are thus less stable and keep less well than saturated
fats Prone to auto-oxidation in the presence of light
(photo-oxidation) which is a reaction of the fats with atmospheric oxygen
Also more prone to hydrogenation (addition of hydrogen) hydrolysis (breaking of the fat back into glycerol and fatty acids) and microbial degradation
Fats and Oils Unsaturated fats are often artificially
hydrogenatedpartially hydrogenated Increases degree of saturation
Allows for control of texture because melting point is affected
Improves stability and shelf life as reactivity is decreased Improves cooking technique where more solid fats are
needed Hydrogen gas is added over a solid nickel catalyst
Double bonds converted to single bonds and degree of saturation increases
Drawback - decreases the health value as fats are healthier when mono- or poly-unsaturated
Ni(s)
Shelf Life Foods gradually become unfit for consumption
due to Spoilage (growth of organisms) Changes in texture smell flavor or appearance
Undesirable processes caused by Change in water content Chemical reactions Exposure to light Changes in temperature
Shelf life is the length of time a product can be stored without these undesirable changes occurring
Shelf Life Change in water content
Causes texture change Loss of water increases exposure to air and thus oxidation
Causes rancidity and discoloration Increase in water encourages microbial growth and
spoilage Chemical reactionstemperature change
Increased temperature increases rates of ldquoharmful reactionsrdquo
Changes in pH or temperature affect the amount of water in a food
Souring with decrease in pH Changes color Can decrease nutritional value
Light provides energy for ldquoharmfulrdquo chemical reactions
Shelf Life Rancidity is a common type of food
degradation Unpleasant textures smells and flavors of fats
and oils
Two types of rancidity Hydrolytic rancidity ndash ester bond in fat is broken
yielding free fatty acids (reverse of formation of a fat) Oxidative rancidity ndash oxygen reacts near the C=C
double bonds in unsaturated fats
Shelf Life Hydrolytic rancidity of fats and oils
reverse of fat formation uses water (hydro lysis = ldquowaterrdquo ldquosplittingrdquo) to split triglycerides back into glycerol and fatty acids
Encouraged by Lipase ndash an enzyme produced by microorganisms Deep frying ndash encourages reaction of fats with moisture in
food Releases free fatty acids
4 ndash 8 carbon fatty acids have a powerfully pungent aromaflavor
palmitic stearic oleic lauric acids give a soapy fatty feel to foods
Shelf Life Oxidative rancidity of fats and oils
Reaction of atmospheric oxygen with fats and oils initiates complex process producing highly reactive free radicals
Products include unpleasant smellingtasting byproducts
More of an issue with increasing degree of unsaturation (more C=C double bonds to react with)
Encouraged by the presence of light (photo-oxidation) Enzymes produced by microorganisms
Shelf Life Oxidative rancidity of fats and oils occurs in 3
steps Initiation by exposure to light ndash produces highly
reactive hydrocarbon radicals (species with an unpaired electron)
R-H R + H Propagation ndash radicals produce other radicals
R + O2 R-O-O ROO + R-H R-O-O-H + R
Termination ndash radicals encounter one another and end the reaction
R + R R-R R-O-O + R-O-O R-O-O-O-O-R R + R-O-O R-O-O-R
(R-H = unsaturated fat or oil R = hydrocarbon radical images on next slide)
Shelf Life Initiation
Shelf Life Propagation
Shelf Life Termination
Shelf Life Shelf life is prolonged by hindering spoilage
processes Packaging
Opaque or darkened packages block light Can be gas impermeable to limit exposure to oxygen and water Can be filled with inert gases or vacuum packed (no gases)
Storage Low temperatures slow harmful reactions Smoking or drying foods removes water and hinder microbial
growth Additives
Salt or sugar added to remove water and hinder microbial growth
KNO3 or NaNO3 salts are reducing agents and can prevent harmful oxidation reactions
Anti-microbial agents Pickling - Organic acids and their salts (ex benzoic acid and
benzoate salts) make pH unfavorable for microbial growth Fermentation ndash production of alcohol hinders microbial growth
Shelf Life Antioxidants delay oxidative degradation
processes by reacting with oxygen to contain free radical formation Can occur naturally
Vitamin C (ascorbic acid) ndash citrus and green vegetables Vitamin E (tocopherol) ndash nuts seeds grains canola oil Beta-carotene ndash carrots broccoli tomatoes peaches Selenium ndash shellfish meat eggs grains Foods high in natural antioxidants green tea blueberries
cranberries dark chocolate turmeric oregano Can be synthetic additives but may have harmful
side effects BHA BHT PG THBP TBHQ
these are all based around a phenol
groupwhich is not
necessarily found in natural
antioxidants
(Full structures in
data booklet)
Shelf Life Types of antioxidants
Free radical quenchers React with radicals to produce less reactive radicals (HA =
quencher)R-O-O + HA R-O-O-H + A
Chelating agents Form very stable complex ions with transition metals (which
can produce radicals) Found naturally in rosemary tea and mustard Salts of the organic acid EDTA are added as artificial chelating
agents Reducing agents
React with oxygen or hydroperoxides Vitamin C or carotenoids are natural reducing agents
Color Foods are colored by either pigments or dyes
Pigments occur naturally Dyes are added artificially and must be tested for
safety Dyes or pigments will absorb a range of light
frequencies and reflect others The color we see in a dye or pigment is the result of
the colors of light reflected not absorbed Ex chlorophyll in green leaf vegetables absorbs red
and blue light reflecting green Molecular structures all involve extensive
delocalized pi bonding (shown on next slide) This system of delocalized pi bonding (conjugated
system) is responsible for the color we see
Color Some of the most common natural pigment
groups are Anthocyanins
Ex Cyanidin Carotenoids
Ex Beta-carotene Chlorophyll
Ex Chlorophyll-A Heme
Ex Heme B group
heme B groupchlorophyll-A
cyanidin
β-carotene
Color Anthocyanins
Responsible for reds pinks blues in berries beets flowers (Flavonones which give color to red grapes and berries are closely related to anthocyanins)
3-ring structures with varying numbers of OH groups in varying positions
Structure and therefore color is related to pH
predominantly red at low pH (acidic) blue at high pH (basic) and colorlesspale yellow at neutral pH
Temperature May break down at high temperatures and cause browning
Exposure to metal Form complexes with iron and aluminum and can change color
Color also affected when anthocyanins bond to sugars
Color Color of anthocyanins is pH dependent (they are
acidbase indicators)
Color Carotenes
Responsible for orange yellow and red colors in foods like carrots bananas tomatoes and saffron
Characterized by long hydrocarbon chains that often have carbon rings on the ends
Have nutritional value precursors to vitamin A (important in vision) act as antioxidants
Relatively stable during food processing but presence of C=C double bonds in hydrocarbon chain opens them up to oxidative degradation as seen in fats
Causes discoloration Prevents carotenoids from being able to be converted to
vitamin A
Color
β-carotene
Color Astaxanthin is a red pigment similar to
carotenoids found in lobster crab and salmon Bonds to proteins in the live animal and gives a
bluegreen color When heated bond to protein is broken which modifies
the structure and frequency of light absorbed appears bright red
Also an antioxidant
Color Chlorophyll
Green pigment responsible for plant photosynthesis Found in green vegetables Structure is centered around a porphyrin ring ndash a
planar ring system with 4 nitrogen atoms surrounding a central metal atom (magnesium in the case of chlorophyll)
Two forms chlorophyll A and chlorophyll B In chlorophyll B an aldehyde side chain replaces a
methyl side chain When cooked plant cells release acids
Causes an H+ ion to replace magnesium atom in center of structure causing a color change to an olivebrown
Opens the possibility for photodegradation (breakdown by light)
Color
chlorophyll A
(replaced with an aldehyde in chlorophyll B)
Color Heme
Pigment found in red blood cells Structure is similar to chlorophyll but there is an iron
atom in the center of the porphyrin ring Found in the protein myoglobin responsible for
oxygen transport Bright red when bound to oxygen but slow process
of autoxidation converts iron from +2 to +3 changing color to brown (less desirable) (myoglobin metmyoglobin)
Color change can be prevented by vacuum packing or packing with an inert gas like CO2
Color
heme groupin myoglobin
Color Color in foods is a result of the structures seen in
anthocyanins carotenoids chlorophylls and hemes All of these structures include an extensive network of
delocalized pi-bonds Alternating single and double bonds is called a conjugated
system The greater the extent of pi bond delocalization the closer
together in energy bonding and antibonding orbitals become All molecules absorb light energy as it promotes e-s between
molecular orbitals (bonding and antibonding orbitals) ndash energy required is proportional to distance between orbitals (less distance = less energy)
As orbitals are close together in a conjugated system low energy light (in the visible region) is absorbed for e- promotion
Color in these groups is the product of visible light absorption - color we see is complementary to the color(s) absorbed
Molecules without an extensive delocalized pi bond network (conjugated system) lack color as orbitals are further apart and only higher energy light promotes e-s (ex the anthocyanin carbinol)
Color Some pigments are water soluble because the
structures contain a large amount of -OH groups (H-bonding) Anthocyanins
Some pigments are fat soluble (ie not water soluble) because their structures contain little or no -OH groups (no H-bonding) carotenoids
Color
Many synthetic dyes are biochemically active and could be potentially harmful
Short-term toxicity easy to test and categorize but long-term effects are more difficult to study
Use of dyes in foods must be regulated but regulations are not standardized internationally posing issues in trade
Color Cooking foods often leads to browning
Two processes responsible Maillard reactions ndash combination of sugars and
proteins Caramelization ndash dehydration of sugar
Both involve removal of water molecule(s)
Color Maillard reactions
Sugars and proteins within the food combine in a condensation reaction
Aldehyde group in sugar (O atom) combines with amino group in protein (2 H atoms)
Initial condensation products polymerize to form brown-colored melanoidins
Maillard reactions only happen gt 140deg C Rate depends on amino acid present (ex lysine
reacts faster than cysteine)
initialcondensationproduct
Color Caramelization
Happens in foods high in carbohydrates Sugars dehydrate (lose H2O) at high temperatures
leaving behind C (dark brown color)
Browning intensifies the longer food is cooked eventually burning it (pure carbon is black)
Rate depends on Sugar type (fructose in fruits caramelizes very quickly) pH ndash extremes (high and low) promote caramelization
Genetically Modified Foods
Produced when organisms with modified DNA are used in food production Used to
Provide pest or disease resistance Bt corn contains toxin from bacillis thuringiensis that kills
insect pests Fungal-resistant potatoes Nematode-resistant bananas (nematode = worm)
Improve quality and range of crop Development of higher-yielding rice varieties Development of corn that can grow in dryer environments
Produce medicines or other products in large quantities Use of chickens that have been modified to lay eggs
containing human interferon (combats tumors and viruses) Use of cows to produce milk rich in omega-3 fatty acids
(polyunsaturated fats essential to growth development brain function)
Moth larva
Genetically Modified Foods
Drawbacks Are GM foods safe Will GM food production alter the natural ecosystem Do we understand enough about genetic
modification GM foods
Can cause allergic reactions in some people Have a slightly different composition from natural foods ndash
alters diet Produce altered pollen ndash might escape and cross with natural
species Long-term effects might be catastrophic unknown so far
Texture Food texture is related to physical properties
Hardness Elasticity Viscosity
These properties can be altered by Cooking Use of dispersed systems
Dispersed system = a stabilized macroscopically homogeneous mixture of two immiscible phases
(this means two substances that would not ordinarily mix ldquoappear tordquo on a macroscopic level (although at the molecular level they are still separate)
Texture Many types of dispersed systems name depends on
the physical states of the substances mixed LiquidSolid or SolidLiquid
Solid particles suspended in a liquid is called a suspension
Ex Blood (blood cells suspended in plasma) Liquid dispersed throughout a solid medium is called a
gel Ex Fruit Jelly (water trapped in a solid protein matrix)
LiquidLiquid Stable blend of two liquids that donrsquot mix is called an
emulsion Ex Mayonaisse (oil droplets suspended in aqueous system)
LiquidGas or GasLiquid Gas bubbles trapped in liquid medium is called a foam
Ex Whipped cream or egg whites Liquid droplets suspended in gas are called aerosols
Ex Aromas from food carried through the air
Texture Dispersed systems will slowly separate over
time Separation can be slowed by adding emulsifiers
Emulsifiers are stabilizers used to keep immiscible substance together
Have surfactant capability (can bind to both substances in suspension)
Similar to micelles in the action of soaps
Ex Lecithin Found commonly in egg
yolks One end is highly charged
and water soluble (bonds toaqueous phase) the otheris not (bonds to non-aqueous phase)
Texture Lecithin in mayonnaise
Lecithin is the emulsifier Mayonnaise made by beating eggs with
vinegar and oil Lecithin is found in eggs ndash charged
hydrophilic end bonds well to vinegar uncharged hydrophobic end bonds to oil
Vigorous beating produces many small oil droplets maximizing surface area for lecithin to act on and produce a stable emulsion
Stabilizers like sodium phosphate or metals are added to prevent separation (chefs use metal bowls)
hydrophilic
hydrophobic
Stereochemistry in Food Many food-specific compounds have a chiral
carbon atom and thus exist as two different enantiomers (optical isomers) Optical isomers are mirror images of one another ldquoOptical activityrdquo refers to the fact that the two mirror
image isomers rotate the direction of plane-polarized light in opposite directions
Enantiomers that rotate polarized light in a clockwise direction are said to be dextrorotatory (dex-tro-rota-tory) and have a + rotational value (d +) ndash In Latin dexter means ldquoright siderdquo
Enantiomers that rotate polarized light in an anti-clockwise direction are said to be laevorotatory (lay-vo-rota-tory) and have a ndash rotational value (l -) ndash In Latin laevus means ldquoleft siderdquo
There are two systems used to provide specific names to each enantiomeric form
Stereochemistry in Food Older system used for naming sugars and amino
acids Enantiomeric forms are labeled ldquoLrdquo and ldquoDrdquo
Again Laevus for left and Dexter for right Based off a compound called glyceraldehyde
chiral carbon
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Nutrients (carbohydrates)
Monosaccharides (ONE sugar) One carbonyl group (C=O) At least two hydroxyl groups (-OH) Empirical formula of CH2O
(carbo C and hydrate H2O) Ex Glucose C6H12O6 Ex Fructose C6H12O6
glucose
fructose
Nutrients (carbohydrates) Disaccharides (TWO
sugars) form when two monosaccharides come together releasing a water molecule (condensation reaction)
ldquoNew bondrdquo is called a glycosidic linkage between the two original monosaccharides
Polysaccharides (MANY sugars aka complex carbohydrates) are the combination of many simple sugars through glycosidic linkages
+ H2O
Nutrients (fats and oils)
Fats and oils are both classified as triglycerides Glycerol (CH2OHCHOHCH2OH) combines
with three fatty acid molecules (fatty = long nonpolar hydrocarbon chain and acid = carboxylic acid)
Also called triesters because of the formation of an ester group when an alcohol group (from glycerol) combines with a carboxylic acid group (from fatty acid)
Nutrients (fats and oils)
Formation of a triglyceride
Nutrients (proteins)
Proteins are polymers of amino acids 20 different amino acid ldquomonomersrdquo
form long chains of near infinite combinations
Typical protein is approximately 300 amino acids but can be made from less or more
Peptide bond (aka amide linkage) bonds amino acids together
+ H2O
Nutrients (water and vitaminsminerals)
Do not provide energy Water is used for transport and
various metabolic processes Vitamins and minerals are also
important in metabolic processes and as enzyme cofactors
Fats and Oils
Properties of a fat (chiefly melting point and chemical stability) are related to The degree of unsaturation ( of double bonds in
the hydrocarbon chains) More double bonds = lower melting point and more
reactive Length of the hydrocarbon chains
Shorter chains = lower melting point Whether the chain is cis or trans isomerized
around double bonds cis = lower melting point
Fats and Oils Saturated ndash all C-C single bonds
Fatty acid has a regular zig-zag shape due to geometry around sp3 hybridized carbon atoms
Monounsaturated ndash one C=C double bond Can be cis or trans isomerized
cis means hydrogen atoms are on same side of double bond trans means hydogen atoms are on opposite sides of the
double bond Polyunsaturated ndash multiple C=C double bonds
Can be either cis or trans isomerized A ldquofatrdquo is a tryglyceride that is solid at room
temperature Usually saturated monounsaturated or trans unsaturated
An oil is a triglyceride that is liquid at room temperature Usually polyunsaturated
Fats and Oils Fats with longer hydrocarbon chains are able to make
more van der Waals forces between each other making molecules harder to separate Higher melting point
Saturated fats have ldquostraightrdquo chains that pack closely and allow for lots of contact between molecules making molecules harder to separate Higher melting point
Trans-unsaturated fats have straight chains just as saturated fats do Higher melting point
Cis-unsaturated fats have irregularly-shaped less ldquostraightrdquo chains Do not pack as closely molecules are easier to separate Lower melting point
Fats and Oils
Fats and Oils ldquoDegree of Crystallizationrdquo is
related to the melting point of a fat Higher melting point means a higher
degree of crystallization (fat is more likely to be solid at room temperature)
Increases with Increasing degree of saturation Increasing amount of trans-unsaturation Higher molecular mass
Naturally-occuring triglycerides most commonly tend to be cis-unsaturated
Fats and Oils cis-unsaturated fats are typically the
healthiest Lower melting point allows for less
buildup of plaque in the arteries that can cause stroke or heart attack
trans-unsaturated fats are less healthy do not commonly occur naturally are harder to metabolize and buildup in fatty tissue Cause an increase in LDL cholesterol
(Low Density Lipoprotein or ldquobadrdquo cholesterol
Fats and Oils Unsaturated oils are more reactive due to the
possibility of addition reactions across the double bonds Are thus less stable and keep less well than saturated
fats Prone to auto-oxidation in the presence of light
(photo-oxidation) which is a reaction of the fats with atmospheric oxygen
Also more prone to hydrogenation (addition of hydrogen) hydrolysis (breaking of the fat back into glycerol and fatty acids) and microbial degradation
Fats and Oils Unsaturated fats are often artificially
hydrogenatedpartially hydrogenated Increases degree of saturation
Allows for control of texture because melting point is affected
Improves stability and shelf life as reactivity is decreased Improves cooking technique where more solid fats are
needed Hydrogen gas is added over a solid nickel catalyst
Double bonds converted to single bonds and degree of saturation increases
Drawback - decreases the health value as fats are healthier when mono- or poly-unsaturated
Ni(s)
Shelf Life Foods gradually become unfit for consumption
due to Spoilage (growth of organisms) Changes in texture smell flavor or appearance
Undesirable processes caused by Change in water content Chemical reactions Exposure to light Changes in temperature
Shelf life is the length of time a product can be stored without these undesirable changes occurring
Shelf Life Change in water content
Causes texture change Loss of water increases exposure to air and thus oxidation
Causes rancidity and discoloration Increase in water encourages microbial growth and
spoilage Chemical reactionstemperature change
Increased temperature increases rates of ldquoharmful reactionsrdquo
Changes in pH or temperature affect the amount of water in a food
Souring with decrease in pH Changes color Can decrease nutritional value
Light provides energy for ldquoharmfulrdquo chemical reactions
Shelf Life Rancidity is a common type of food
degradation Unpleasant textures smells and flavors of fats
and oils
Two types of rancidity Hydrolytic rancidity ndash ester bond in fat is broken
yielding free fatty acids (reverse of formation of a fat) Oxidative rancidity ndash oxygen reacts near the C=C
double bonds in unsaturated fats
Shelf Life Hydrolytic rancidity of fats and oils
reverse of fat formation uses water (hydro lysis = ldquowaterrdquo ldquosplittingrdquo) to split triglycerides back into glycerol and fatty acids
Encouraged by Lipase ndash an enzyme produced by microorganisms Deep frying ndash encourages reaction of fats with moisture in
food Releases free fatty acids
4 ndash 8 carbon fatty acids have a powerfully pungent aromaflavor
palmitic stearic oleic lauric acids give a soapy fatty feel to foods
Shelf Life Oxidative rancidity of fats and oils
Reaction of atmospheric oxygen with fats and oils initiates complex process producing highly reactive free radicals
Products include unpleasant smellingtasting byproducts
More of an issue with increasing degree of unsaturation (more C=C double bonds to react with)
Encouraged by the presence of light (photo-oxidation) Enzymes produced by microorganisms
Shelf Life Oxidative rancidity of fats and oils occurs in 3
steps Initiation by exposure to light ndash produces highly
reactive hydrocarbon radicals (species with an unpaired electron)
R-H R + H Propagation ndash radicals produce other radicals
R + O2 R-O-O ROO + R-H R-O-O-H + R
Termination ndash radicals encounter one another and end the reaction
R + R R-R R-O-O + R-O-O R-O-O-O-O-R R + R-O-O R-O-O-R
(R-H = unsaturated fat or oil R = hydrocarbon radical images on next slide)
Shelf Life Initiation
Shelf Life Propagation
Shelf Life Termination
Shelf Life Shelf life is prolonged by hindering spoilage
processes Packaging
Opaque or darkened packages block light Can be gas impermeable to limit exposure to oxygen and water Can be filled with inert gases or vacuum packed (no gases)
Storage Low temperatures slow harmful reactions Smoking or drying foods removes water and hinder microbial
growth Additives
Salt or sugar added to remove water and hinder microbial growth
KNO3 or NaNO3 salts are reducing agents and can prevent harmful oxidation reactions
Anti-microbial agents Pickling - Organic acids and their salts (ex benzoic acid and
benzoate salts) make pH unfavorable for microbial growth Fermentation ndash production of alcohol hinders microbial growth
Shelf Life Antioxidants delay oxidative degradation
processes by reacting with oxygen to contain free radical formation Can occur naturally
Vitamin C (ascorbic acid) ndash citrus and green vegetables Vitamin E (tocopherol) ndash nuts seeds grains canola oil Beta-carotene ndash carrots broccoli tomatoes peaches Selenium ndash shellfish meat eggs grains Foods high in natural antioxidants green tea blueberries
cranberries dark chocolate turmeric oregano Can be synthetic additives but may have harmful
side effects BHA BHT PG THBP TBHQ
these are all based around a phenol
groupwhich is not
necessarily found in natural
antioxidants
(Full structures in
data booklet)
Shelf Life Types of antioxidants
Free radical quenchers React with radicals to produce less reactive radicals (HA =
quencher)R-O-O + HA R-O-O-H + A
Chelating agents Form very stable complex ions with transition metals (which
can produce radicals) Found naturally in rosemary tea and mustard Salts of the organic acid EDTA are added as artificial chelating
agents Reducing agents
React with oxygen or hydroperoxides Vitamin C or carotenoids are natural reducing agents
Color Foods are colored by either pigments or dyes
Pigments occur naturally Dyes are added artificially and must be tested for
safety Dyes or pigments will absorb a range of light
frequencies and reflect others The color we see in a dye or pigment is the result of
the colors of light reflected not absorbed Ex chlorophyll in green leaf vegetables absorbs red
and blue light reflecting green Molecular structures all involve extensive
delocalized pi bonding (shown on next slide) This system of delocalized pi bonding (conjugated
system) is responsible for the color we see
Color Some of the most common natural pigment
groups are Anthocyanins
Ex Cyanidin Carotenoids
Ex Beta-carotene Chlorophyll
Ex Chlorophyll-A Heme
Ex Heme B group
heme B groupchlorophyll-A
cyanidin
β-carotene
Color Anthocyanins
Responsible for reds pinks blues in berries beets flowers (Flavonones which give color to red grapes and berries are closely related to anthocyanins)
3-ring structures with varying numbers of OH groups in varying positions
Structure and therefore color is related to pH
predominantly red at low pH (acidic) blue at high pH (basic) and colorlesspale yellow at neutral pH
Temperature May break down at high temperatures and cause browning
Exposure to metal Form complexes with iron and aluminum and can change color
Color also affected when anthocyanins bond to sugars
Color Color of anthocyanins is pH dependent (they are
acidbase indicators)
Color Carotenes
Responsible for orange yellow and red colors in foods like carrots bananas tomatoes and saffron
Characterized by long hydrocarbon chains that often have carbon rings on the ends
Have nutritional value precursors to vitamin A (important in vision) act as antioxidants
Relatively stable during food processing but presence of C=C double bonds in hydrocarbon chain opens them up to oxidative degradation as seen in fats
Causes discoloration Prevents carotenoids from being able to be converted to
vitamin A
Color
β-carotene
Color Astaxanthin is a red pigment similar to
carotenoids found in lobster crab and salmon Bonds to proteins in the live animal and gives a
bluegreen color When heated bond to protein is broken which modifies
the structure and frequency of light absorbed appears bright red
Also an antioxidant
Color Chlorophyll
Green pigment responsible for plant photosynthesis Found in green vegetables Structure is centered around a porphyrin ring ndash a
planar ring system with 4 nitrogen atoms surrounding a central metal atom (magnesium in the case of chlorophyll)
Two forms chlorophyll A and chlorophyll B In chlorophyll B an aldehyde side chain replaces a
methyl side chain When cooked plant cells release acids
Causes an H+ ion to replace magnesium atom in center of structure causing a color change to an olivebrown
Opens the possibility for photodegradation (breakdown by light)
Color
chlorophyll A
(replaced with an aldehyde in chlorophyll B)
Color Heme
Pigment found in red blood cells Structure is similar to chlorophyll but there is an iron
atom in the center of the porphyrin ring Found in the protein myoglobin responsible for
oxygen transport Bright red when bound to oxygen but slow process
of autoxidation converts iron from +2 to +3 changing color to brown (less desirable) (myoglobin metmyoglobin)
Color change can be prevented by vacuum packing or packing with an inert gas like CO2
Color
heme groupin myoglobin
Color Color in foods is a result of the structures seen in
anthocyanins carotenoids chlorophylls and hemes All of these structures include an extensive network of
delocalized pi-bonds Alternating single and double bonds is called a conjugated
system The greater the extent of pi bond delocalization the closer
together in energy bonding and antibonding orbitals become All molecules absorb light energy as it promotes e-s between
molecular orbitals (bonding and antibonding orbitals) ndash energy required is proportional to distance between orbitals (less distance = less energy)
As orbitals are close together in a conjugated system low energy light (in the visible region) is absorbed for e- promotion
Color in these groups is the product of visible light absorption - color we see is complementary to the color(s) absorbed
Molecules without an extensive delocalized pi bond network (conjugated system) lack color as orbitals are further apart and only higher energy light promotes e-s (ex the anthocyanin carbinol)
Color Some pigments are water soluble because the
structures contain a large amount of -OH groups (H-bonding) Anthocyanins
Some pigments are fat soluble (ie not water soluble) because their structures contain little or no -OH groups (no H-bonding) carotenoids
Color
Many synthetic dyes are biochemically active and could be potentially harmful
Short-term toxicity easy to test and categorize but long-term effects are more difficult to study
Use of dyes in foods must be regulated but regulations are not standardized internationally posing issues in trade
Color Cooking foods often leads to browning
Two processes responsible Maillard reactions ndash combination of sugars and
proteins Caramelization ndash dehydration of sugar
Both involve removal of water molecule(s)
Color Maillard reactions
Sugars and proteins within the food combine in a condensation reaction
Aldehyde group in sugar (O atom) combines with amino group in protein (2 H atoms)
Initial condensation products polymerize to form brown-colored melanoidins
Maillard reactions only happen gt 140deg C Rate depends on amino acid present (ex lysine
reacts faster than cysteine)
initialcondensationproduct
Color Caramelization
Happens in foods high in carbohydrates Sugars dehydrate (lose H2O) at high temperatures
leaving behind C (dark brown color)
Browning intensifies the longer food is cooked eventually burning it (pure carbon is black)
Rate depends on Sugar type (fructose in fruits caramelizes very quickly) pH ndash extremes (high and low) promote caramelization
Genetically Modified Foods
Produced when organisms with modified DNA are used in food production Used to
Provide pest or disease resistance Bt corn contains toxin from bacillis thuringiensis that kills
insect pests Fungal-resistant potatoes Nematode-resistant bananas (nematode = worm)
Improve quality and range of crop Development of higher-yielding rice varieties Development of corn that can grow in dryer environments
Produce medicines or other products in large quantities Use of chickens that have been modified to lay eggs
containing human interferon (combats tumors and viruses) Use of cows to produce milk rich in omega-3 fatty acids
(polyunsaturated fats essential to growth development brain function)
Moth larva
Genetically Modified Foods
Drawbacks Are GM foods safe Will GM food production alter the natural ecosystem Do we understand enough about genetic
modification GM foods
Can cause allergic reactions in some people Have a slightly different composition from natural foods ndash
alters diet Produce altered pollen ndash might escape and cross with natural
species Long-term effects might be catastrophic unknown so far
Texture Food texture is related to physical properties
Hardness Elasticity Viscosity
These properties can be altered by Cooking Use of dispersed systems
Dispersed system = a stabilized macroscopically homogeneous mixture of two immiscible phases
(this means two substances that would not ordinarily mix ldquoappear tordquo on a macroscopic level (although at the molecular level they are still separate)
Texture Many types of dispersed systems name depends on
the physical states of the substances mixed LiquidSolid or SolidLiquid
Solid particles suspended in a liquid is called a suspension
Ex Blood (blood cells suspended in plasma) Liquid dispersed throughout a solid medium is called a
gel Ex Fruit Jelly (water trapped in a solid protein matrix)
LiquidLiquid Stable blend of two liquids that donrsquot mix is called an
emulsion Ex Mayonaisse (oil droplets suspended in aqueous system)
LiquidGas or GasLiquid Gas bubbles trapped in liquid medium is called a foam
Ex Whipped cream or egg whites Liquid droplets suspended in gas are called aerosols
Ex Aromas from food carried through the air
Texture Dispersed systems will slowly separate over
time Separation can be slowed by adding emulsifiers
Emulsifiers are stabilizers used to keep immiscible substance together
Have surfactant capability (can bind to both substances in suspension)
Similar to micelles in the action of soaps
Ex Lecithin Found commonly in egg
yolks One end is highly charged
and water soluble (bonds toaqueous phase) the otheris not (bonds to non-aqueous phase)
Texture Lecithin in mayonnaise
Lecithin is the emulsifier Mayonnaise made by beating eggs with
vinegar and oil Lecithin is found in eggs ndash charged
hydrophilic end bonds well to vinegar uncharged hydrophobic end bonds to oil
Vigorous beating produces many small oil droplets maximizing surface area for lecithin to act on and produce a stable emulsion
Stabilizers like sodium phosphate or metals are added to prevent separation (chefs use metal bowls)
hydrophilic
hydrophobic
Stereochemistry in Food Many food-specific compounds have a chiral
carbon atom and thus exist as two different enantiomers (optical isomers) Optical isomers are mirror images of one another ldquoOptical activityrdquo refers to the fact that the two mirror
image isomers rotate the direction of plane-polarized light in opposite directions
Enantiomers that rotate polarized light in a clockwise direction are said to be dextrorotatory (dex-tro-rota-tory) and have a + rotational value (d +) ndash In Latin dexter means ldquoright siderdquo
Enantiomers that rotate polarized light in an anti-clockwise direction are said to be laevorotatory (lay-vo-rota-tory) and have a ndash rotational value (l -) ndash In Latin laevus means ldquoleft siderdquo
There are two systems used to provide specific names to each enantiomeric form
Stereochemistry in Food Older system used for naming sugars and amino
acids Enantiomeric forms are labeled ldquoLrdquo and ldquoDrdquo
Again Laevus for left and Dexter for right Based off a compound called glyceraldehyde
chiral carbon
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Nutrients (carbohydrates) Disaccharides (TWO
sugars) form when two monosaccharides come together releasing a water molecule (condensation reaction)
ldquoNew bondrdquo is called a glycosidic linkage between the two original monosaccharides
Polysaccharides (MANY sugars aka complex carbohydrates) are the combination of many simple sugars through glycosidic linkages
+ H2O
Nutrients (fats and oils)
Fats and oils are both classified as triglycerides Glycerol (CH2OHCHOHCH2OH) combines
with three fatty acid molecules (fatty = long nonpolar hydrocarbon chain and acid = carboxylic acid)
Also called triesters because of the formation of an ester group when an alcohol group (from glycerol) combines with a carboxylic acid group (from fatty acid)
Nutrients (fats and oils)
Formation of a triglyceride
Nutrients (proteins)
Proteins are polymers of amino acids 20 different amino acid ldquomonomersrdquo
form long chains of near infinite combinations
Typical protein is approximately 300 amino acids but can be made from less or more
Peptide bond (aka amide linkage) bonds amino acids together
+ H2O
Nutrients (water and vitaminsminerals)
Do not provide energy Water is used for transport and
various metabolic processes Vitamins and minerals are also
important in metabolic processes and as enzyme cofactors
Fats and Oils
Properties of a fat (chiefly melting point and chemical stability) are related to The degree of unsaturation ( of double bonds in
the hydrocarbon chains) More double bonds = lower melting point and more
reactive Length of the hydrocarbon chains
Shorter chains = lower melting point Whether the chain is cis or trans isomerized
around double bonds cis = lower melting point
Fats and Oils Saturated ndash all C-C single bonds
Fatty acid has a regular zig-zag shape due to geometry around sp3 hybridized carbon atoms
Monounsaturated ndash one C=C double bond Can be cis or trans isomerized
cis means hydrogen atoms are on same side of double bond trans means hydogen atoms are on opposite sides of the
double bond Polyunsaturated ndash multiple C=C double bonds
Can be either cis or trans isomerized A ldquofatrdquo is a tryglyceride that is solid at room
temperature Usually saturated monounsaturated or trans unsaturated
An oil is a triglyceride that is liquid at room temperature Usually polyunsaturated
Fats and Oils Fats with longer hydrocarbon chains are able to make
more van der Waals forces between each other making molecules harder to separate Higher melting point
Saturated fats have ldquostraightrdquo chains that pack closely and allow for lots of contact between molecules making molecules harder to separate Higher melting point
Trans-unsaturated fats have straight chains just as saturated fats do Higher melting point
Cis-unsaturated fats have irregularly-shaped less ldquostraightrdquo chains Do not pack as closely molecules are easier to separate Lower melting point
Fats and Oils
Fats and Oils ldquoDegree of Crystallizationrdquo is
related to the melting point of a fat Higher melting point means a higher
degree of crystallization (fat is more likely to be solid at room temperature)
Increases with Increasing degree of saturation Increasing amount of trans-unsaturation Higher molecular mass
Naturally-occuring triglycerides most commonly tend to be cis-unsaturated
Fats and Oils cis-unsaturated fats are typically the
healthiest Lower melting point allows for less
buildup of plaque in the arteries that can cause stroke or heart attack
trans-unsaturated fats are less healthy do not commonly occur naturally are harder to metabolize and buildup in fatty tissue Cause an increase in LDL cholesterol
(Low Density Lipoprotein or ldquobadrdquo cholesterol
Fats and Oils Unsaturated oils are more reactive due to the
possibility of addition reactions across the double bonds Are thus less stable and keep less well than saturated
fats Prone to auto-oxidation in the presence of light
(photo-oxidation) which is a reaction of the fats with atmospheric oxygen
Also more prone to hydrogenation (addition of hydrogen) hydrolysis (breaking of the fat back into glycerol and fatty acids) and microbial degradation
Fats and Oils Unsaturated fats are often artificially
hydrogenatedpartially hydrogenated Increases degree of saturation
Allows for control of texture because melting point is affected
Improves stability and shelf life as reactivity is decreased Improves cooking technique where more solid fats are
needed Hydrogen gas is added over a solid nickel catalyst
Double bonds converted to single bonds and degree of saturation increases
Drawback - decreases the health value as fats are healthier when mono- or poly-unsaturated
Ni(s)
Shelf Life Foods gradually become unfit for consumption
due to Spoilage (growth of organisms) Changes in texture smell flavor or appearance
Undesirable processes caused by Change in water content Chemical reactions Exposure to light Changes in temperature
Shelf life is the length of time a product can be stored without these undesirable changes occurring
Shelf Life Change in water content
Causes texture change Loss of water increases exposure to air and thus oxidation
Causes rancidity and discoloration Increase in water encourages microbial growth and
spoilage Chemical reactionstemperature change
Increased temperature increases rates of ldquoharmful reactionsrdquo
Changes in pH or temperature affect the amount of water in a food
Souring with decrease in pH Changes color Can decrease nutritional value
Light provides energy for ldquoharmfulrdquo chemical reactions
Shelf Life Rancidity is a common type of food
degradation Unpleasant textures smells and flavors of fats
and oils
Two types of rancidity Hydrolytic rancidity ndash ester bond in fat is broken
yielding free fatty acids (reverse of formation of a fat) Oxidative rancidity ndash oxygen reacts near the C=C
double bonds in unsaturated fats
Shelf Life Hydrolytic rancidity of fats and oils
reverse of fat formation uses water (hydro lysis = ldquowaterrdquo ldquosplittingrdquo) to split triglycerides back into glycerol and fatty acids
Encouraged by Lipase ndash an enzyme produced by microorganisms Deep frying ndash encourages reaction of fats with moisture in
food Releases free fatty acids
4 ndash 8 carbon fatty acids have a powerfully pungent aromaflavor
palmitic stearic oleic lauric acids give a soapy fatty feel to foods
Shelf Life Oxidative rancidity of fats and oils
Reaction of atmospheric oxygen with fats and oils initiates complex process producing highly reactive free radicals
Products include unpleasant smellingtasting byproducts
More of an issue with increasing degree of unsaturation (more C=C double bonds to react with)
Encouraged by the presence of light (photo-oxidation) Enzymes produced by microorganisms
Shelf Life Oxidative rancidity of fats and oils occurs in 3
steps Initiation by exposure to light ndash produces highly
reactive hydrocarbon radicals (species with an unpaired electron)
R-H R + H Propagation ndash radicals produce other radicals
R + O2 R-O-O ROO + R-H R-O-O-H + R
Termination ndash radicals encounter one another and end the reaction
R + R R-R R-O-O + R-O-O R-O-O-O-O-R R + R-O-O R-O-O-R
(R-H = unsaturated fat or oil R = hydrocarbon radical images on next slide)
Shelf Life Initiation
Shelf Life Propagation
Shelf Life Termination
Shelf Life Shelf life is prolonged by hindering spoilage
processes Packaging
Opaque or darkened packages block light Can be gas impermeable to limit exposure to oxygen and water Can be filled with inert gases or vacuum packed (no gases)
Storage Low temperatures slow harmful reactions Smoking or drying foods removes water and hinder microbial
growth Additives
Salt or sugar added to remove water and hinder microbial growth
KNO3 or NaNO3 salts are reducing agents and can prevent harmful oxidation reactions
Anti-microbial agents Pickling - Organic acids and their salts (ex benzoic acid and
benzoate salts) make pH unfavorable for microbial growth Fermentation ndash production of alcohol hinders microbial growth
Shelf Life Antioxidants delay oxidative degradation
processes by reacting with oxygen to contain free radical formation Can occur naturally
Vitamin C (ascorbic acid) ndash citrus and green vegetables Vitamin E (tocopherol) ndash nuts seeds grains canola oil Beta-carotene ndash carrots broccoli tomatoes peaches Selenium ndash shellfish meat eggs grains Foods high in natural antioxidants green tea blueberries
cranberries dark chocolate turmeric oregano Can be synthetic additives but may have harmful
side effects BHA BHT PG THBP TBHQ
these are all based around a phenol
groupwhich is not
necessarily found in natural
antioxidants
(Full structures in
data booklet)
Shelf Life Types of antioxidants
Free radical quenchers React with radicals to produce less reactive radicals (HA =
quencher)R-O-O + HA R-O-O-H + A
Chelating agents Form very stable complex ions with transition metals (which
can produce radicals) Found naturally in rosemary tea and mustard Salts of the organic acid EDTA are added as artificial chelating
agents Reducing agents
React with oxygen or hydroperoxides Vitamin C or carotenoids are natural reducing agents
Color Foods are colored by either pigments or dyes
Pigments occur naturally Dyes are added artificially and must be tested for
safety Dyes or pigments will absorb a range of light
frequencies and reflect others The color we see in a dye or pigment is the result of
the colors of light reflected not absorbed Ex chlorophyll in green leaf vegetables absorbs red
and blue light reflecting green Molecular structures all involve extensive
delocalized pi bonding (shown on next slide) This system of delocalized pi bonding (conjugated
system) is responsible for the color we see
Color Some of the most common natural pigment
groups are Anthocyanins
Ex Cyanidin Carotenoids
Ex Beta-carotene Chlorophyll
Ex Chlorophyll-A Heme
Ex Heme B group
heme B groupchlorophyll-A
cyanidin
β-carotene
Color Anthocyanins
Responsible for reds pinks blues in berries beets flowers (Flavonones which give color to red grapes and berries are closely related to anthocyanins)
3-ring structures with varying numbers of OH groups in varying positions
Structure and therefore color is related to pH
predominantly red at low pH (acidic) blue at high pH (basic) and colorlesspale yellow at neutral pH
Temperature May break down at high temperatures and cause browning
Exposure to metal Form complexes with iron and aluminum and can change color
Color also affected when anthocyanins bond to sugars
Color Color of anthocyanins is pH dependent (they are
acidbase indicators)
Color Carotenes
Responsible for orange yellow and red colors in foods like carrots bananas tomatoes and saffron
Characterized by long hydrocarbon chains that often have carbon rings on the ends
Have nutritional value precursors to vitamin A (important in vision) act as antioxidants
Relatively stable during food processing but presence of C=C double bonds in hydrocarbon chain opens them up to oxidative degradation as seen in fats
Causes discoloration Prevents carotenoids from being able to be converted to
vitamin A
Color
β-carotene
Color Astaxanthin is a red pigment similar to
carotenoids found in lobster crab and salmon Bonds to proteins in the live animal and gives a
bluegreen color When heated bond to protein is broken which modifies
the structure and frequency of light absorbed appears bright red
Also an antioxidant
Color Chlorophyll
Green pigment responsible for plant photosynthesis Found in green vegetables Structure is centered around a porphyrin ring ndash a
planar ring system with 4 nitrogen atoms surrounding a central metal atom (magnesium in the case of chlorophyll)
Two forms chlorophyll A and chlorophyll B In chlorophyll B an aldehyde side chain replaces a
methyl side chain When cooked plant cells release acids
Causes an H+ ion to replace magnesium atom in center of structure causing a color change to an olivebrown
Opens the possibility for photodegradation (breakdown by light)
Color
chlorophyll A
(replaced with an aldehyde in chlorophyll B)
Color Heme
Pigment found in red blood cells Structure is similar to chlorophyll but there is an iron
atom in the center of the porphyrin ring Found in the protein myoglobin responsible for
oxygen transport Bright red when bound to oxygen but slow process
of autoxidation converts iron from +2 to +3 changing color to brown (less desirable) (myoglobin metmyoglobin)
Color change can be prevented by vacuum packing or packing with an inert gas like CO2
Color
heme groupin myoglobin
Color Color in foods is a result of the structures seen in
anthocyanins carotenoids chlorophylls and hemes All of these structures include an extensive network of
delocalized pi-bonds Alternating single and double bonds is called a conjugated
system The greater the extent of pi bond delocalization the closer
together in energy bonding and antibonding orbitals become All molecules absorb light energy as it promotes e-s between
molecular orbitals (bonding and antibonding orbitals) ndash energy required is proportional to distance between orbitals (less distance = less energy)
As orbitals are close together in a conjugated system low energy light (in the visible region) is absorbed for e- promotion
Color in these groups is the product of visible light absorption - color we see is complementary to the color(s) absorbed
Molecules without an extensive delocalized pi bond network (conjugated system) lack color as orbitals are further apart and only higher energy light promotes e-s (ex the anthocyanin carbinol)
Color Some pigments are water soluble because the
structures contain a large amount of -OH groups (H-bonding) Anthocyanins
Some pigments are fat soluble (ie not water soluble) because their structures contain little or no -OH groups (no H-bonding) carotenoids
Color
Many synthetic dyes are biochemically active and could be potentially harmful
Short-term toxicity easy to test and categorize but long-term effects are more difficult to study
Use of dyes in foods must be regulated but regulations are not standardized internationally posing issues in trade
Color Cooking foods often leads to browning
Two processes responsible Maillard reactions ndash combination of sugars and
proteins Caramelization ndash dehydration of sugar
Both involve removal of water molecule(s)
Color Maillard reactions
Sugars and proteins within the food combine in a condensation reaction
Aldehyde group in sugar (O atom) combines with amino group in protein (2 H atoms)
Initial condensation products polymerize to form brown-colored melanoidins
Maillard reactions only happen gt 140deg C Rate depends on amino acid present (ex lysine
reacts faster than cysteine)
initialcondensationproduct
Color Caramelization
Happens in foods high in carbohydrates Sugars dehydrate (lose H2O) at high temperatures
leaving behind C (dark brown color)
Browning intensifies the longer food is cooked eventually burning it (pure carbon is black)
Rate depends on Sugar type (fructose in fruits caramelizes very quickly) pH ndash extremes (high and low) promote caramelization
Genetically Modified Foods
Produced when organisms with modified DNA are used in food production Used to
Provide pest or disease resistance Bt corn contains toxin from bacillis thuringiensis that kills
insect pests Fungal-resistant potatoes Nematode-resistant bananas (nematode = worm)
Improve quality and range of crop Development of higher-yielding rice varieties Development of corn that can grow in dryer environments
Produce medicines or other products in large quantities Use of chickens that have been modified to lay eggs
containing human interferon (combats tumors and viruses) Use of cows to produce milk rich in omega-3 fatty acids
(polyunsaturated fats essential to growth development brain function)
Moth larva
Genetically Modified Foods
Drawbacks Are GM foods safe Will GM food production alter the natural ecosystem Do we understand enough about genetic
modification GM foods
Can cause allergic reactions in some people Have a slightly different composition from natural foods ndash
alters diet Produce altered pollen ndash might escape and cross with natural
species Long-term effects might be catastrophic unknown so far
Texture Food texture is related to physical properties
Hardness Elasticity Viscosity
These properties can be altered by Cooking Use of dispersed systems
Dispersed system = a stabilized macroscopically homogeneous mixture of two immiscible phases
(this means two substances that would not ordinarily mix ldquoappear tordquo on a macroscopic level (although at the molecular level they are still separate)
Texture Many types of dispersed systems name depends on
the physical states of the substances mixed LiquidSolid or SolidLiquid
Solid particles suspended in a liquid is called a suspension
Ex Blood (blood cells suspended in plasma) Liquid dispersed throughout a solid medium is called a
gel Ex Fruit Jelly (water trapped in a solid protein matrix)
LiquidLiquid Stable blend of two liquids that donrsquot mix is called an
emulsion Ex Mayonaisse (oil droplets suspended in aqueous system)
LiquidGas or GasLiquid Gas bubbles trapped in liquid medium is called a foam
Ex Whipped cream or egg whites Liquid droplets suspended in gas are called aerosols
Ex Aromas from food carried through the air
Texture Dispersed systems will slowly separate over
time Separation can be slowed by adding emulsifiers
Emulsifiers are stabilizers used to keep immiscible substance together
Have surfactant capability (can bind to both substances in suspension)
Similar to micelles in the action of soaps
Ex Lecithin Found commonly in egg
yolks One end is highly charged
and water soluble (bonds toaqueous phase) the otheris not (bonds to non-aqueous phase)
Texture Lecithin in mayonnaise
Lecithin is the emulsifier Mayonnaise made by beating eggs with
vinegar and oil Lecithin is found in eggs ndash charged
hydrophilic end bonds well to vinegar uncharged hydrophobic end bonds to oil
Vigorous beating produces many small oil droplets maximizing surface area for lecithin to act on and produce a stable emulsion
Stabilizers like sodium phosphate or metals are added to prevent separation (chefs use metal bowls)
hydrophilic
hydrophobic
Stereochemistry in Food Many food-specific compounds have a chiral
carbon atom and thus exist as two different enantiomers (optical isomers) Optical isomers are mirror images of one another ldquoOptical activityrdquo refers to the fact that the two mirror
image isomers rotate the direction of plane-polarized light in opposite directions
Enantiomers that rotate polarized light in a clockwise direction are said to be dextrorotatory (dex-tro-rota-tory) and have a + rotational value (d +) ndash In Latin dexter means ldquoright siderdquo
Enantiomers that rotate polarized light in an anti-clockwise direction are said to be laevorotatory (lay-vo-rota-tory) and have a ndash rotational value (l -) ndash In Latin laevus means ldquoleft siderdquo
There are two systems used to provide specific names to each enantiomeric form
Stereochemistry in Food Older system used for naming sugars and amino
acids Enantiomeric forms are labeled ldquoLrdquo and ldquoDrdquo
Again Laevus for left and Dexter for right Based off a compound called glyceraldehyde
chiral carbon
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Nutrients (fats and oils)
Fats and oils are both classified as triglycerides Glycerol (CH2OHCHOHCH2OH) combines
with three fatty acid molecules (fatty = long nonpolar hydrocarbon chain and acid = carboxylic acid)
Also called triesters because of the formation of an ester group when an alcohol group (from glycerol) combines with a carboxylic acid group (from fatty acid)
Nutrients (fats and oils)
Formation of a triglyceride
Nutrients (proteins)
Proteins are polymers of amino acids 20 different amino acid ldquomonomersrdquo
form long chains of near infinite combinations
Typical protein is approximately 300 amino acids but can be made from less or more
Peptide bond (aka amide linkage) bonds amino acids together
+ H2O
Nutrients (water and vitaminsminerals)
Do not provide energy Water is used for transport and
various metabolic processes Vitamins and minerals are also
important in metabolic processes and as enzyme cofactors
Fats and Oils
Properties of a fat (chiefly melting point and chemical stability) are related to The degree of unsaturation ( of double bonds in
the hydrocarbon chains) More double bonds = lower melting point and more
reactive Length of the hydrocarbon chains
Shorter chains = lower melting point Whether the chain is cis or trans isomerized
around double bonds cis = lower melting point
Fats and Oils Saturated ndash all C-C single bonds
Fatty acid has a regular zig-zag shape due to geometry around sp3 hybridized carbon atoms
Monounsaturated ndash one C=C double bond Can be cis or trans isomerized
cis means hydrogen atoms are on same side of double bond trans means hydogen atoms are on opposite sides of the
double bond Polyunsaturated ndash multiple C=C double bonds
Can be either cis or trans isomerized A ldquofatrdquo is a tryglyceride that is solid at room
temperature Usually saturated monounsaturated or trans unsaturated
An oil is a triglyceride that is liquid at room temperature Usually polyunsaturated
Fats and Oils Fats with longer hydrocarbon chains are able to make
more van der Waals forces between each other making molecules harder to separate Higher melting point
Saturated fats have ldquostraightrdquo chains that pack closely and allow for lots of contact between molecules making molecules harder to separate Higher melting point
Trans-unsaturated fats have straight chains just as saturated fats do Higher melting point
Cis-unsaturated fats have irregularly-shaped less ldquostraightrdquo chains Do not pack as closely molecules are easier to separate Lower melting point
Fats and Oils
Fats and Oils ldquoDegree of Crystallizationrdquo is
related to the melting point of a fat Higher melting point means a higher
degree of crystallization (fat is more likely to be solid at room temperature)
Increases with Increasing degree of saturation Increasing amount of trans-unsaturation Higher molecular mass
Naturally-occuring triglycerides most commonly tend to be cis-unsaturated
Fats and Oils cis-unsaturated fats are typically the
healthiest Lower melting point allows for less
buildup of plaque in the arteries that can cause stroke or heart attack
trans-unsaturated fats are less healthy do not commonly occur naturally are harder to metabolize and buildup in fatty tissue Cause an increase in LDL cholesterol
(Low Density Lipoprotein or ldquobadrdquo cholesterol
Fats and Oils Unsaturated oils are more reactive due to the
possibility of addition reactions across the double bonds Are thus less stable and keep less well than saturated
fats Prone to auto-oxidation in the presence of light
(photo-oxidation) which is a reaction of the fats with atmospheric oxygen
Also more prone to hydrogenation (addition of hydrogen) hydrolysis (breaking of the fat back into glycerol and fatty acids) and microbial degradation
Fats and Oils Unsaturated fats are often artificially
hydrogenatedpartially hydrogenated Increases degree of saturation
Allows for control of texture because melting point is affected
Improves stability and shelf life as reactivity is decreased Improves cooking technique where more solid fats are
needed Hydrogen gas is added over a solid nickel catalyst
Double bonds converted to single bonds and degree of saturation increases
Drawback - decreases the health value as fats are healthier when mono- or poly-unsaturated
Ni(s)
Shelf Life Foods gradually become unfit for consumption
due to Spoilage (growth of organisms) Changes in texture smell flavor or appearance
Undesirable processes caused by Change in water content Chemical reactions Exposure to light Changes in temperature
Shelf life is the length of time a product can be stored without these undesirable changes occurring
Shelf Life Change in water content
Causes texture change Loss of water increases exposure to air and thus oxidation
Causes rancidity and discoloration Increase in water encourages microbial growth and
spoilage Chemical reactionstemperature change
Increased temperature increases rates of ldquoharmful reactionsrdquo
Changes in pH or temperature affect the amount of water in a food
Souring with decrease in pH Changes color Can decrease nutritional value
Light provides energy for ldquoharmfulrdquo chemical reactions
Shelf Life Rancidity is a common type of food
degradation Unpleasant textures smells and flavors of fats
and oils
Two types of rancidity Hydrolytic rancidity ndash ester bond in fat is broken
yielding free fatty acids (reverse of formation of a fat) Oxidative rancidity ndash oxygen reacts near the C=C
double bonds in unsaturated fats
Shelf Life Hydrolytic rancidity of fats and oils
reverse of fat formation uses water (hydro lysis = ldquowaterrdquo ldquosplittingrdquo) to split triglycerides back into glycerol and fatty acids
Encouraged by Lipase ndash an enzyme produced by microorganisms Deep frying ndash encourages reaction of fats with moisture in
food Releases free fatty acids
4 ndash 8 carbon fatty acids have a powerfully pungent aromaflavor
palmitic stearic oleic lauric acids give a soapy fatty feel to foods
Shelf Life Oxidative rancidity of fats and oils
Reaction of atmospheric oxygen with fats and oils initiates complex process producing highly reactive free radicals
Products include unpleasant smellingtasting byproducts
More of an issue with increasing degree of unsaturation (more C=C double bonds to react with)
Encouraged by the presence of light (photo-oxidation) Enzymes produced by microorganisms
Shelf Life Oxidative rancidity of fats and oils occurs in 3
steps Initiation by exposure to light ndash produces highly
reactive hydrocarbon radicals (species with an unpaired electron)
R-H R + H Propagation ndash radicals produce other radicals
R + O2 R-O-O ROO + R-H R-O-O-H + R
Termination ndash radicals encounter one another and end the reaction
R + R R-R R-O-O + R-O-O R-O-O-O-O-R R + R-O-O R-O-O-R
(R-H = unsaturated fat or oil R = hydrocarbon radical images on next slide)
Shelf Life Initiation
Shelf Life Propagation
Shelf Life Termination
Shelf Life Shelf life is prolonged by hindering spoilage
processes Packaging
Opaque or darkened packages block light Can be gas impermeable to limit exposure to oxygen and water Can be filled with inert gases or vacuum packed (no gases)
Storage Low temperatures slow harmful reactions Smoking or drying foods removes water and hinder microbial
growth Additives
Salt or sugar added to remove water and hinder microbial growth
KNO3 or NaNO3 salts are reducing agents and can prevent harmful oxidation reactions
Anti-microbial agents Pickling - Organic acids and their salts (ex benzoic acid and
benzoate salts) make pH unfavorable for microbial growth Fermentation ndash production of alcohol hinders microbial growth
Shelf Life Antioxidants delay oxidative degradation
processes by reacting with oxygen to contain free radical formation Can occur naturally
Vitamin C (ascorbic acid) ndash citrus and green vegetables Vitamin E (tocopherol) ndash nuts seeds grains canola oil Beta-carotene ndash carrots broccoli tomatoes peaches Selenium ndash shellfish meat eggs grains Foods high in natural antioxidants green tea blueberries
cranberries dark chocolate turmeric oregano Can be synthetic additives but may have harmful
side effects BHA BHT PG THBP TBHQ
these are all based around a phenol
groupwhich is not
necessarily found in natural
antioxidants
(Full structures in
data booklet)
Shelf Life Types of antioxidants
Free radical quenchers React with radicals to produce less reactive radicals (HA =
quencher)R-O-O + HA R-O-O-H + A
Chelating agents Form very stable complex ions with transition metals (which
can produce radicals) Found naturally in rosemary tea and mustard Salts of the organic acid EDTA are added as artificial chelating
agents Reducing agents
React with oxygen or hydroperoxides Vitamin C or carotenoids are natural reducing agents
Color Foods are colored by either pigments or dyes
Pigments occur naturally Dyes are added artificially and must be tested for
safety Dyes or pigments will absorb a range of light
frequencies and reflect others The color we see in a dye or pigment is the result of
the colors of light reflected not absorbed Ex chlorophyll in green leaf vegetables absorbs red
and blue light reflecting green Molecular structures all involve extensive
delocalized pi bonding (shown on next slide) This system of delocalized pi bonding (conjugated
system) is responsible for the color we see
Color Some of the most common natural pigment
groups are Anthocyanins
Ex Cyanidin Carotenoids
Ex Beta-carotene Chlorophyll
Ex Chlorophyll-A Heme
Ex Heme B group
heme B groupchlorophyll-A
cyanidin
β-carotene
Color Anthocyanins
Responsible for reds pinks blues in berries beets flowers (Flavonones which give color to red grapes and berries are closely related to anthocyanins)
3-ring structures with varying numbers of OH groups in varying positions
Structure and therefore color is related to pH
predominantly red at low pH (acidic) blue at high pH (basic) and colorlesspale yellow at neutral pH
Temperature May break down at high temperatures and cause browning
Exposure to metal Form complexes with iron and aluminum and can change color
Color also affected when anthocyanins bond to sugars
Color Color of anthocyanins is pH dependent (they are
acidbase indicators)
Color Carotenes
Responsible for orange yellow and red colors in foods like carrots bananas tomatoes and saffron
Characterized by long hydrocarbon chains that often have carbon rings on the ends
Have nutritional value precursors to vitamin A (important in vision) act as antioxidants
Relatively stable during food processing but presence of C=C double bonds in hydrocarbon chain opens them up to oxidative degradation as seen in fats
Causes discoloration Prevents carotenoids from being able to be converted to
vitamin A
Color
β-carotene
Color Astaxanthin is a red pigment similar to
carotenoids found in lobster crab and salmon Bonds to proteins in the live animal and gives a
bluegreen color When heated bond to protein is broken which modifies
the structure and frequency of light absorbed appears bright red
Also an antioxidant
Color Chlorophyll
Green pigment responsible for plant photosynthesis Found in green vegetables Structure is centered around a porphyrin ring ndash a
planar ring system with 4 nitrogen atoms surrounding a central metal atom (magnesium in the case of chlorophyll)
Two forms chlorophyll A and chlorophyll B In chlorophyll B an aldehyde side chain replaces a
methyl side chain When cooked plant cells release acids
Causes an H+ ion to replace magnesium atom in center of structure causing a color change to an olivebrown
Opens the possibility for photodegradation (breakdown by light)
Color
chlorophyll A
(replaced with an aldehyde in chlorophyll B)
Color Heme
Pigment found in red blood cells Structure is similar to chlorophyll but there is an iron
atom in the center of the porphyrin ring Found in the protein myoglobin responsible for
oxygen transport Bright red when bound to oxygen but slow process
of autoxidation converts iron from +2 to +3 changing color to brown (less desirable) (myoglobin metmyoglobin)
Color change can be prevented by vacuum packing or packing with an inert gas like CO2
Color
heme groupin myoglobin
Color Color in foods is a result of the structures seen in
anthocyanins carotenoids chlorophylls and hemes All of these structures include an extensive network of
delocalized pi-bonds Alternating single and double bonds is called a conjugated
system The greater the extent of pi bond delocalization the closer
together in energy bonding and antibonding orbitals become All molecules absorb light energy as it promotes e-s between
molecular orbitals (bonding and antibonding orbitals) ndash energy required is proportional to distance between orbitals (less distance = less energy)
As orbitals are close together in a conjugated system low energy light (in the visible region) is absorbed for e- promotion
Color in these groups is the product of visible light absorption - color we see is complementary to the color(s) absorbed
Molecules without an extensive delocalized pi bond network (conjugated system) lack color as orbitals are further apart and only higher energy light promotes e-s (ex the anthocyanin carbinol)
Color Some pigments are water soluble because the
structures contain a large amount of -OH groups (H-bonding) Anthocyanins
Some pigments are fat soluble (ie not water soluble) because their structures contain little or no -OH groups (no H-bonding) carotenoids
Color
Many synthetic dyes are biochemically active and could be potentially harmful
Short-term toxicity easy to test and categorize but long-term effects are more difficult to study
Use of dyes in foods must be regulated but regulations are not standardized internationally posing issues in trade
Color Cooking foods often leads to browning
Two processes responsible Maillard reactions ndash combination of sugars and
proteins Caramelization ndash dehydration of sugar
Both involve removal of water molecule(s)
Color Maillard reactions
Sugars and proteins within the food combine in a condensation reaction
Aldehyde group in sugar (O atom) combines with amino group in protein (2 H atoms)
Initial condensation products polymerize to form brown-colored melanoidins
Maillard reactions only happen gt 140deg C Rate depends on amino acid present (ex lysine
reacts faster than cysteine)
initialcondensationproduct
Color Caramelization
Happens in foods high in carbohydrates Sugars dehydrate (lose H2O) at high temperatures
leaving behind C (dark brown color)
Browning intensifies the longer food is cooked eventually burning it (pure carbon is black)
Rate depends on Sugar type (fructose in fruits caramelizes very quickly) pH ndash extremes (high and low) promote caramelization
Genetically Modified Foods
Produced when organisms with modified DNA are used in food production Used to
Provide pest or disease resistance Bt corn contains toxin from bacillis thuringiensis that kills
insect pests Fungal-resistant potatoes Nematode-resistant bananas (nematode = worm)
Improve quality and range of crop Development of higher-yielding rice varieties Development of corn that can grow in dryer environments
Produce medicines or other products in large quantities Use of chickens that have been modified to lay eggs
containing human interferon (combats tumors and viruses) Use of cows to produce milk rich in omega-3 fatty acids
(polyunsaturated fats essential to growth development brain function)
Moth larva
Genetically Modified Foods
Drawbacks Are GM foods safe Will GM food production alter the natural ecosystem Do we understand enough about genetic
modification GM foods
Can cause allergic reactions in some people Have a slightly different composition from natural foods ndash
alters diet Produce altered pollen ndash might escape and cross with natural
species Long-term effects might be catastrophic unknown so far
Texture Food texture is related to physical properties
Hardness Elasticity Viscosity
These properties can be altered by Cooking Use of dispersed systems
Dispersed system = a stabilized macroscopically homogeneous mixture of two immiscible phases
(this means two substances that would not ordinarily mix ldquoappear tordquo on a macroscopic level (although at the molecular level they are still separate)
Texture Many types of dispersed systems name depends on
the physical states of the substances mixed LiquidSolid or SolidLiquid
Solid particles suspended in a liquid is called a suspension
Ex Blood (blood cells suspended in plasma) Liquid dispersed throughout a solid medium is called a
gel Ex Fruit Jelly (water trapped in a solid protein matrix)
LiquidLiquid Stable blend of two liquids that donrsquot mix is called an
emulsion Ex Mayonaisse (oil droplets suspended in aqueous system)
LiquidGas or GasLiquid Gas bubbles trapped in liquid medium is called a foam
Ex Whipped cream or egg whites Liquid droplets suspended in gas are called aerosols
Ex Aromas from food carried through the air
Texture Dispersed systems will slowly separate over
time Separation can be slowed by adding emulsifiers
Emulsifiers are stabilizers used to keep immiscible substance together
Have surfactant capability (can bind to both substances in suspension)
Similar to micelles in the action of soaps
Ex Lecithin Found commonly in egg
yolks One end is highly charged
and water soluble (bonds toaqueous phase) the otheris not (bonds to non-aqueous phase)
Texture Lecithin in mayonnaise
Lecithin is the emulsifier Mayonnaise made by beating eggs with
vinegar and oil Lecithin is found in eggs ndash charged
hydrophilic end bonds well to vinegar uncharged hydrophobic end bonds to oil
Vigorous beating produces many small oil droplets maximizing surface area for lecithin to act on and produce a stable emulsion
Stabilizers like sodium phosphate or metals are added to prevent separation (chefs use metal bowls)
hydrophilic
hydrophobic
Stereochemistry in Food Many food-specific compounds have a chiral
carbon atom and thus exist as two different enantiomers (optical isomers) Optical isomers are mirror images of one another ldquoOptical activityrdquo refers to the fact that the two mirror
image isomers rotate the direction of plane-polarized light in opposite directions
Enantiomers that rotate polarized light in a clockwise direction are said to be dextrorotatory (dex-tro-rota-tory) and have a + rotational value (d +) ndash In Latin dexter means ldquoright siderdquo
Enantiomers that rotate polarized light in an anti-clockwise direction are said to be laevorotatory (lay-vo-rota-tory) and have a ndash rotational value (l -) ndash In Latin laevus means ldquoleft siderdquo
There are two systems used to provide specific names to each enantiomeric form
Stereochemistry in Food Older system used for naming sugars and amino
acids Enantiomeric forms are labeled ldquoLrdquo and ldquoDrdquo
Again Laevus for left and Dexter for right Based off a compound called glyceraldehyde
chiral carbon
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Nutrients (fats and oils)
Formation of a triglyceride
Nutrients (proteins)
Proteins are polymers of amino acids 20 different amino acid ldquomonomersrdquo
form long chains of near infinite combinations
Typical protein is approximately 300 amino acids but can be made from less or more
Peptide bond (aka amide linkage) bonds amino acids together
+ H2O
Nutrients (water and vitaminsminerals)
Do not provide energy Water is used for transport and
various metabolic processes Vitamins and minerals are also
important in metabolic processes and as enzyme cofactors
Fats and Oils
Properties of a fat (chiefly melting point and chemical stability) are related to The degree of unsaturation ( of double bonds in
the hydrocarbon chains) More double bonds = lower melting point and more
reactive Length of the hydrocarbon chains
Shorter chains = lower melting point Whether the chain is cis or trans isomerized
around double bonds cis = lower melting point
Fats and Oils Saturated ndash all C-C single bonds
Fatty acid has a regular zig-zag shape due to geometry around sp3 hybridized carbon atoms
Monounsaturated ndash one C=C double bond Can be cis or trans isomerized
cis means hydrogen atoms are on same side of double bond trans means hydogen atoms are on opposite sides of the
double bond Polyunsaturated ndash multiple C=C double bonds
Can be either cis or trans isomerized A ldquofatrdquo is a tryglyceride that is solid at room
temperature Usually saturated monounsaturated or trans unsaturated
An oil is a triglyceride that is liquid at room temperature Usually polyunsaturated
Fats and Oils Fats with longer hydrocarbon chains are able to make
more van der Waals forces between each other making molecules harder to separate Higher melting point
Saturated fats have ldquostraightrdquo chains that pack closely and allow for lots of contact between molecules making molecules harder to separate Higher melting point
Trans-unsaturated fats have straight chains just as saturated fats do Higher melting point
Cis-unsaturated fats have irregularly-shaped less ldquostraightrdquo chains Do not pack as closely molecules are easier to separate Lower melting point
Fats and Oils
Fats and Oils ldquoDegree of Crystallizationrdquo is
related to the melting point of a fat Higher melting point means a higher
degree of crystallization (fat is more likely to be solid at room temperature)
Increases with Increasing degree of saturation Increasing amount of trans-unsaturation Higher molecular mass
Naturally-occuring triglycerides most commonly tend to be cis-unsaturated
Fats and Oils cis-unsaturated fats are typically the
healthiest Lower melting point allows for less
buildup of plaque in the arteries that can cause stroke or heart attack
trans-unsaturated fats are less healthy do not commonly occur naturally are harder to metabolize and buildup in fatty tissue Cause an increase in LDL cholesterol
(Low Density Lipoprotein or ldquobadrdquo cholesterol
Fats and Oils Unsaturated oils are more reactive due to the
possibility of addition reactions across the double bonds Are thus less stable and keep less well than saturated
fats Prone to auto-oxidation in the presence of light
(photo-oxidation) which is a reaction of the fats with atmospheric oxygen
Also more prone to hydrogenation (addition of hydrogen) hydrolysis (breaking of the fat back into glycerol and fatty acids) and microbial degradation
Fats and Oils Unsaturated fats are often artificially
hydrogenatedpartially hydrogenated Increases degree of saturation
Allows for control of texture because melting point is affected
Improves stability and shelf life as reactivity is decreased Improves cooking technique where more solid fats are
needed Hydrogen gas is added over a solid nickel catalyst
Double bonds converted to single bonds and degree of saturation increases
Drawback - decreases the health value as fats are healthier when mono- or poly-unsaturated
Ni(s)
Shelf Life Foods gradually become unfit for consumption
due to Spoilage (growth of organisms) Changes in texture smell flavor or appearance
Undesirable processes caused by Change in water content Chemical reactions Exposure to light Changes in temperature
Shelf life is the length of time a product can be stored without these undesirable changes occurring
Shelf Life Change in water content
Causes texture change Loss of water increases exposure to air and thus oxidation
Causes rancidity and discoloration Increase in water encourages microbial growth and
spoilage Chemical reactionstemperature change
Increased temperature increases rates of ldquoharmful reactionsrdquo
Changes in pH or temperature affect the amount of water in a food
Souring with decrease in pH Changes color Can decrease nutritional value
Light provides energy for ldquoharmfulrdquo chemical reactions
Shelf Life Rancidity is a common type of food
degradation Unpleasant textures smells and flavors of fats
and oils
Two types of rancidity Hydrolytic rancidity ndash ester bond in fat is broken
yielding free fatty acids (reverse of formation of a fat) Oxidative rancidity ndash oxygen reacts near the C=C
double bonds in unsaturated fats
Shelf Life Hydrolytic rancidity of fats and oils
reverse of fat formation uses water (hydro lysis = ldquowaterrdquo ldquosplittingrdquo) to split triglycerides back into glycerol and fatty acids
Encouraged by Lipase ndash an enzyme produced by microorganisms Deep frying ndash encourages reaction of fats with moisture in
food Releases free fatty acids
4 ndash 8 carbon fatty acids have a powerfully pungent aromaflavor
palmitic stearic oleic lauric acids give a soapy fatty feel to foods
Shelf Life Oxidative rancidity of fats and oils
Reaction of atmospheric oxygen with fats and oils initiates complex process producing highly reactive free radicals
Products include unpleasant smellingtasting byproducts
More of an issue with increasing degree of unsaturation (more C=C double bonds to react with)
Encouraged by the presence of light (photo-oxidation) Enzymes produced by microorganisms
Shelf Life Oxidative rancidity of fats and oils occurs in 3
steps Initiation by exposure to light ndash produces highly
reactive hydrocarbon radicals (species with an unpaired electron)
R-H R + H Propagation ndash radicals produce other radicals
R + O2 R-O-O ROO + R-H R-O-O-H + R
Termination ndash radicals encounter one another and end the reaction
R + R R-R R-O-O + R-O-O R-O-O-O-O-R R + R-O-O R-O-O-R
(R-H = unsaturated fat or oil R = hydrocarbon radical images on next slide)
Shelf Life Initiation
Shelf Life Propagation
Shelf Life Termination
Shelf Life Shelf life is prolonged by hindering spoilage
processes Packaging
Opaque or darkened packages block light Can be gas impermeable to limit exposure to oxygen and water Can be filled with inert gases or vacuum packed (no gases)
Storage Low temperatures slow harmful reactions Smoking or drying foods removes water and hinder microbial
growth Additives
Salt or sugar added to remove water and hinder microbial growth
KNO3 or NaNO3 salts are reducing agents and can prevent harmful oxidation reactions
Anti-microbial agents Pickling - Organic acids and their salts (ex benzoic acid and
benzoate salts) make pH unfavorable for microbial growth Fermentation ndash production of alcohol hinders microbial growth
Shelf Life Antioxidants delay oxidative degradation
processes by reacting with oxygen to contain free radical formation Can occur naturally
Vitamin C (ascorbic acid) ndash citrus and green vegetables Vitamin E (tocopherol) ndash nuts seeds grains canola oil Beta-carotene ndash carrots broccoli tomatoes peaches Selenium ndash shellfish meat eggs grains Foods high in natural antioxidants green tea blueberries
cranberries dark chocolate turmeric oregano Can be synthetic additives but may have harmful
side effects BHA BHT PG THBP TBHQ
these are all based around a phenol
groupwhich is not
necessarily found in natural
antioxidants
(Full structures in
data booklet)
Shelf Life Types of antioxidants
Free radical quenchers React with radicals to produce less reactive radicals (HA =
quencher)R-O-O + HA R-O-O-H + A
Chelating agents Form very stable complex ions with transition metals (which
can produce radicals) Found naturally in rosemary tea and mustard Salts of the organic acid EDTA are added as artificial chelating
agents Reducing agents
React with oxygen or hydroperoxides Vitamin C or carotenoids are natural reducing agents
Color Foods are colored by either pigments or dyes
Pigments occur naturally Dyes are added artificially and must be tested for
safety Dyes or pigments will absorb a range of light
frequencies and reflect others The color we see in a dye or pigment is the result of
the colors of light reflected not absorbed Ex chlorophyll in green leaf vegetables absorbs red
and blue light reflecting green Molecular structures all involve extensive
delocalized pi bonding (shown on next slide) This system of delocalized pi bonding (conjugated
system) is responsible for the color we see
Color Some of the most common natural pigment
groups are Anthocyanins
Ex Cyanidin Carotenoids
Ex Beta-carotene Chlorophyll
Ex Chlorophyll-A Heme
Ex Heme B group
heme B groupchlorophyll-A
cyanidin
β-carotene
Color Anthocyanins
Responsible for reds pinks blues in berries beets flowers (Flavonones which give color to red grapes and berries are closely related to anthocyanins)
3-ring structures with varying numbers of OH groups in varying positions
Structure and therefore color is related to pH
predominantly red at low pH (acidic) blue at high pH (basic) and colorlesspale yellow at neutral pH
Temperature May break down at high temperatures and cause browning
Exposure to metal Form complexes with iron and aluminum and can change color
Color also affected when anthocyanins bond to sugars
Color Color of anthocyanins is pH dependent (they are
acidbase indicators)
Color Carotenes
Responsible for orange yellow and red colors in foods like carrots bananas tomatoes and saffron
Characterized by long hydrocarbon chains that often have carbon rings on the ends
Have nutritional value precursors to vitamin A (important in vision) act as antioxidants
Relatively stable during food processing but presence of C=C double bonds in hydrocarbon chain opens them up to oxidative degradation as seen in fats
Causes discoloration Prevents carotenoids from being able to be converted to
vitamin A
Color
β-carotene
Color Astaxanthin is a red pigment similar to
carotenoids found in lobster crab and salmon Bonds to proteins in the live animal and gives a
bluegreen color When heated bond to protein is broken which modifies
the structure and frequency of light absorbed appears bright red
Also an antioxidant
Color Chlorophyll
Green pigment responsible for plant photosynthesis Found in green vegetables Structure is centered around a porphyrin ring ndash a
planar ring system with 4 nitrogen atoms surrounding a central metal atom (magnesium in the case of chlorophyll)
Two forms chlorophyll A and chlorophyll B In chlorophyll B an aldehyde side chain replaces a
methyl side chain When cooked plant cells release acids
Causes an H+ ion to replace magnesium atom in center of structure causing a color change to an olivebrown
Opens the possibility for photodegradation (breakdown by light)
Color
chlorophyll A
(replaced with an aldehyde in chlorophyll B)
Color Heme
Pigment found in red blood cells Structure is similar to chlorophyll but there is an iron
atom in the center of the porphyrin ring Found in the protein myoglobin responsible for
oxygen transport Bright red when bound to oxygen but slow process
of autoxidation converts iron from +2 to +3 changing color to brown (less desirable) (myoglobin metmyoglobin)
Color change can be prevented by vacuum packing or packing with an inert gas like CO2
Color
heme groupin myoglobin
Color Color in foods is a result of the structures seen in
anthocyanins carotenoids chlorophylls and hemes All of these structures include an extensive network of
delocalized pi-bonds Alternating single and double bonds is called a conjugated
system The greater the extent of pi bond delocalization the closer
together in energy bonding and antibonding orbitals become All molecules absorb light energy as it promotes e-s between
molecular orbitals (bonding and antibonding orbitals) ndash energy required is proportional to distance between orbitals (less distance = less energy)
As orbitals are close together in a conjugated system low energy light (in the visible region) is absorbed for e- promotion
Color in these groups is the product of visible light absorption - color we see is complementary to the color(s) absorbed
Molecules without an extensive delocalized pi bond network (conjugated system) lack color as orbitals are further apart and only higher energy light promotes e-s (ex the anthocyanin carbinol)
Color Some pigments are water soluble because the
structures contain a large amount of -OH groups (H-bonding) Anthocyanins
Some pigments are fat soluble (ie not water soluble) because their structures contain little or no -OH groups (no H-bonding) carotenoids
Color
Many synthetic dyes are biochemically active and could be potentially harmful
Short-term toxicity easy to test and categorize but long-term effects are more difficult to study
Use of dyes in foods must be regulated but regulations are not standardized internationally posing issues in trade
Color Cooking foods often leads to browning
Two processes responsible Maillard reactions ndash combination of sugars and
proteins Caramelization ndash dehydration of sugar
Both involve removal of water molecule(s)
Color Maillard reactions
Sugars and proteins within the food combine in a condensation reaction
Aldehyde group in sugar (O atom) combines with amino group in protein (2 H atoms)
Initial condensation products polymerize to form brown-colored melanoidins
Maillard reactions only happen gt 140deg C Rate depends on amino acid present (ex lysine
reacts faster than cysteine)
initialcondensationproduct
Color Caramelization
Happens in foods high in carbohydrates Sugars dehydrate (lose H2O) at high temperatures
leaving behind C (dark brown color)
Browning intensifies the longer food is cooked eventually burning it (pure carbon is black)
Rate depends on Sugar type (fructose in fruits caramelizes very quickly) pH ndash extremes (high and low) promote caramelization
Genetically Modified Foods
Produced when organisms with modified DNA are used in food production Used to
Provide pest or disease resistance Bt corn contains toxin from bacillis thuringiensis that kills
insect pests Fungal-resistant potatoes Nematode-resistant bananas (nematode = worm)
Improve quality and range of crop Development of higher-yielding rice varieties Development of corn that can grow in dryer environments
Produce medicines or other products in large quantities Use of chickens that have been modified to lay eggs
containing human interferon (combats tumors and viruses) Use of cows to produce milk rich in omega-3 fatty acids
(polyunsaturated fats essential to growth development brain function)
Moth larva
Genetically Modified Foods
Drawbacks Are GM foods safe Will GM food production alter the natural ecosystem Do we understand enough about genetic
modification GM foods
Can cause allergic reactions in some people Have a slightly different composition from natural foods ndash
alters diet Produce altered pollen ndash might escape and cross with natural
species Long-term effects might be catastrophic unknown so far
Texture Food texture is related to physical properties
Hardness Elasticity Viscosity
These properties can be altered by Cooking Use of dispersed systems
Dispersed system = a stabilized macroscopically homogeneous mixture of two immiscible phases
(this means two substances that would not ordinarily mix ldquoappear tordquo on a macroscopic level (although at the molecular level they are still separate)
Texture Many types of dispersed systems name depends on
the physical states of the substances mixed LiquidSolid or SolidLiquid
Solid particles suspended in a liquid is called a suspension
Ex Blood (blood cells suspended in plasma) Liquid dispersed throughout a solid medium is called a
gel Ex Fruit Jelly (water trapped in a solid protein matrix)
LiquidLiquid Stable blend of two liquids that donrsquot mix is called an
emulsion Ex Mayonaisse (oil droplets suspended in aqueous system)
LiquidGas or GasLiquid Gas bubbles trapped in liquid medium is called a foam
Ex Whipped cream or egg whites Liquid droplets suspended in gas are called aerosols
Ex Aromas from food carried through the air
Texture Dispersed systems will slowly separate over
time Separation can be slowed by adding emulsifiers
Emulsifiers are stabilizers used to keep immiscible substance together
Have surfactant capability (can bind to both substances in suspension)
Similar to micelles in the action of soaps
Ex Lecithin Found commonly in egg
yolks One end is highly charged
and water soluble (bonds toaqueous phase) the otheris not (bonds to non-aqueous phase)
Texture Lecithin in mayonnaise
Lecithin is the emulsifier Mayonnaise made by beating eggs with
vinegar and oil Lecithin is found in eggs ndash charged
hydrophilic end bonds well to vinegar uncharged hydrophobic end bonds to oil
Vigorous beating produces many small oil droplets maximizing surface area for lecithin to act on and produce a stable emulsion
Stabilizers like sodium phosphate or metals are added to prevent separation (chefs use metal bowls)
hydrophilic
hydrophobic
Stereochemistry in Food Many food-specific compounds have a chiral
carbon atom and thus exist as two different enantiomers (optical isomers) Optical isomers are mirror images of one another ldquoOptical activityrdquo refers to the fact that the two mirror
image isomers rotate the direction of plane-polarized light in opposite directions
Enantiomers that rotate polarized light in a clockwise direction are said to be dextrorotatory (dex-tro-rota-tory) and have a + rotational value (d +) ndash In Latin dexter means ldquoright siderdquo
Enantiomers that rotate polarized light in an anti-clockwise direction are said to be laevorotatory (lay-vo-rota-tory) and have a ndash rotational value (l -) ndash In Latin laevus means ldquoleft siderdquo
There are two systems used to provide specific names to each enantiomeric form
Stereochemistry in Food Older system used for naming sugars and amino
acids Enantiomeric forms are labeled ldquoLrdquo and ldquoDrdquo
Again Laevus for left and Dexter for right Based off a compound called glyceraldehyde
chiral carbon
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Nutrients (proteins)
Proteins are polymers of amino acids 20 different amino acid ldquomonomersrdquo
form long chains of near infinite combinations
Typical protein is approximately 300 amino acids but can be made from less or more
Peptide bond (aka amide linkage) bonds amino acids together
+ H2O
Nutrients (water and vitaminsminerals)
Do not provide energy Water is used for transport and
various metabolic processes Vitamins and minerals are also
important in metabolic processes and as enzyme cofactors
Fats and Oils
Properties of a fat (chiefly melting point and chemical stability) are related to The degree of unsaturation ( of double bonds in
the hydrocarbon chains) More double bonds = lower melting point and more
reactive Length of the hydrocarbon chains
Shorter chains = lower melting point Whether the chain is cis or trans isomerized
around double bonds cis = lower melting point
Fats and Oils Saturated ndash all C-C single bonds
Fatty acid has a regular zig-zag shape due to geometry around sp3 hybridized carbon atoms
Monounsaturated ndash one C=C double bond Can be cis or trans isomerized
cis means hydrogen atoms are on same side of double bond trans means hydogen atoms are on opposite sides of the
double bond Polyunsaturated ndash multiple C=C double bonds
Can be either cis or trans isomerized A ldquofatrdquo is a tryglyceride that is solid at room
temperature Usually saturated monounsaturated or trans unsaturated
An oil is a triglyceride that is liquid at room temperature Usually polyunsaturated
Fats and Oils Fats with longer hydrocarbon chains are able to make
more van der Waals forces between each other making molecules harder to separate Higher melting point
Saturated fats have ldquostraightrdquo chains that pack closely and allow for lots of contact between molecules making molecules harder to separate Higher melting point
Trans-unsaturated fats have straight chains just as saturated fats do Higher melting point
Cis-unsaturated fats have irregularly-shaped less ldquostraightrdquo chains Do not pack as closely molecules are easier to separate Lower melting point
Fats and Oils
Fats and Oils ldquoDegree of Crystallizationrdquo is
related to the melting point of a fat Higher melting point means a higher
degree of crystallization (fat is more likely to be solid at room temperature)
Increases with Increasing degree of saturation Increasing amount of trans-unsaturation Higher molecular mass
Naturally-occuring triglycerides most commonly tend to be cis-unsaturated
Fats and Oils cis-unsaturated fats are typically the
healthiest Lower melting point allows for less
buildup of plaque in the arteries that can cause stroke or heart attack
trans-unsaturated fats are less healthy do not commonly occur naturally are harder to metabolize and buildup in fatty tissue Cause an increase in LDL cholesterol
(Low Density Lipoprotein or ldquobadrdquo cholesterol
Fats and Oils Unsaturated oils are more reactive due to the
possibility of addition reactions across the double bonds Are thus less stable and keep less well than saturated
fats Prone to auto-oxidation in the presence of light
(photo-oxidation) which is a reaction of the fats with atmospheric oxygen
Also more prone to hydrogenation (addition of hydrogen) hydrolysis (breaking of the fat back into glycerol and fatty acids) and microbial degradation
Fats and Oils Unsaturated fats are often artificially
hydrogenatedpartially hydrogenated Increases degree of saturation
Allows for control of texture because melting point is affected
Improves stability and shelf life as reactivity is decreased Improves cooking technique where more solid fats are
needed Hydrogen gas is added over a solid nickel catalyst
Double bonds converted to single bonds and degree of saturation increases
Drawback - decreases the health value as fats are healthier when mono- or poly-unsaturated
Ni(s)
Shelf Life Foods gradually become unfit for consumption
due to Spoilage (growth of organisms) Changes in texture smell flavor or appearance
Undesirable processes caused by Change in water content Chemical reactions Exposure to light Changes in temperature
Shelf life is the length of time a product can be stored without these undesirable changes occurring
Shelf Life Change in water content
Causes texture change Loss of water increases exposure to air and thus oxidation
Causes rancidity and discoloration Increase in water encourages microbial growth and
spoilage Chemical reactionstemperature change
Increased temperature increases rates of ldquoharmful reactionsrdquo
Changes in pH or temperature affect the amount of water in a food
Souring with decrease in pH Changes color Can decrease nutritional value
Light provides energy for ldquoharmfulrdquo chemical reactions
Shelf Life Rancidity is a common type of food
degradation Unpleasant textures smells and flavors of fats
and oils
Two types of rancidity Hydrolytic rancidity ndash ester bond in fat is broken
yielding free fatty acids (reverse of formation of a fat) Oxidative rancidity ndash oxygen reacts near the C=C
double bonds in unsaturated fats
Shelf Life Hydrolytic rancidity of fats and oils
reverse of fat formation uses water (hydro lysis = ldquowaterrdquo ldquosplittingrdquo) to split triglycerides back into glycerol and fatty acids
Encouraged by Lipase ndash an enzyme produced by microorganisms Deep frying ndash encourages reaction of fats with moisture in
food Releases free fatty acids
4 ndash 8 carbon fatty acids have a powerfully pungent aromaflavor
palmitic stearic oleic lauric acids give a soapy fatty feel to foods
Shelf Life Oxidative rancidity of fats and oils
Reaction of atmospheric oxygen with fats and oils initiates complex process producing highly reactive free radicals
Products include unpleasant smellingtasting byproducts
More of an issue with increasing degree of unsaturation (more C=C double bonds to react with)
Encouraged by the presence of light (photo-oxidation) Enzymes produced by microorganisms
Shelf Life Oxidative rancidity of fats and oils occurs in 3
steps Initiation by exposure to light ndash produces highly
reactive hydrocarbon radicals (species with an unpaired electron)
R-H R + H Propagation ndash radicals produce other radicals
R + O2 R-O-O ROO + R-H R-O-O-H + R
Termination ndash radicals encounter one another and end the reaction
R + R R-R R-O-O + R-O-O R-O-O-O-O-R R + R-O-O R-O-O-R
(R-H = unsaturated fat or oil R = hydrocarbon radical images on next slide)
Shelf Life Initiation
Shelf Life Propagation
Shelf Life Termination
Shelf Life Shelf life is prolonged by hindering spoilage
processes Packaging
Opaque or darkened packages block light Can be gas impermeable to limit exposure to oxygen and water Can be filled with inert gases or vacuum packed (no gases)
Storage Low temperatures slow harmful reactions Smoking or drying foods removes water and hinder microbial
growth Additives
Salt or sugar added to remove water and hinder microbial growth
KNO3 or NaNO3 salts are reducing agents and can prevent harmful oxidation reactions
Anti-microbial agents Pickling - Organic acids and their salts (ex benzoic acid and
benzoate salts) make pH unfavorable for microbial growth Fermentation ndash production of alcohol hinders microbial growth
Shelf Life Antioxidants delay oxidative degradation
processes by reacting with oxygen to contain free radical formation Can occur naturally
Vitamin C (ascorbic acid) ndash citrus and green vegetables Vitamin E (tocopherol) ndash nuts seeds grains canola oil Beta-carotene ndash carrots broccoli tomatoes peaches Selenium ndash shellfish meat eggs grains Foods high in natural antioxidants green tea blueberries
cranberries dark chocolate turmeric oregano Can be synthetic additives but may have harmful
side effects BHA BHT PG THBP TBHQ
these are all based around a phenol
groupwhich is not
necessarily found in natural
antioxidants
(Full structures in
data booklet)
Shelf Life Types of antioxidants
Free radical quenchers React with radicals to produce less reactive radicals (HA =
quencher)R-O-O + HA R-O-O-H + A
Chelating agents Form very stable complex ions with transition metals (which
can produce radicals) Found naturally in rosemary tea and mustard Salts of the organic acid EDTA are added as artificial chelating
agents Reducing agents
React with oxygen or hydroperoxides Vitamin C or carotenoids are natural reducing agents
Color Foods are colored by either pigments or dyes
Pigments occur naturally Dyes are added artificially and must be tested for
safety Dyes or pigments will absorb a range of light
frequencies and reflect others The color we see in a dye or pigment is the result of
the colors of light reflected not absorbed Ex chlorophyll in green leaf vegetables absorbs red
and blue light reflecting green Molecular structures all involve extensive
delocalized pi bonding (shown on next slide) This system of delocalized pi bonding (conjugated
system) is responsible for the color we see
Color Some of the most common natural pigment
groups are Anthocyanins
Ex Cyanidin Carotenoids
Ex Beta-carotene Chlorophyll
Ex Chlorophyll-A Heme
Ex Heme B group
heme B groupchlorophyll-A
cyanidin
β-carotene
Color Anthocyanins
Responsible for reds pinks blues in berries beets flowers (Flavonones which give color to red grapes and berries are closely related to anthocyanins)
3-ring structures with varying numbers of OH groups in varying positions
Structure and therefore color is related to pH
predominantly red at low pH (acidic) blue at high pH (basic) and colorlesspale yellow at neutral pH
Temperature May break down at high temperatures and cause browning
Exposure to metal Form complexes with iron and aluminum and can change color
Color also affected when anthocyanins bond to sugars
Color Color of anthocyanins is pH dependent (they are
acidbase indicators)
Color Carotenes
Responsible for orange yellow and red colors in foods like carrots bananas tomatoes and saffron
Characterized by long hydrocarbon chains that often have carbon rings on the ends
Have nutritional value precursors to vitamin A (important in vision) act as antioxidants
Relatively stable during food processing but presence of C=C double bonds in hydrocarbon chain opens them up to oxidative degradation as seen in fats
Causes discoloration Prevents carotenoids from being able to be converted to
vitamin A
Color
β-carotene
Color Astaxanthin is a red pigment similar to
carotenoids found in lobster crab and salmon Bonds to proteins in the live animal and gives a
bluegreen color When heated bond to protein is broken which modifies
the structure and frequency of light absorbed appears bright red
Also an antioxidant
Color Chlorophyll
Green pigment responsible for plant photosynthesis Found in green vegetables Structure is centered around a porphyrin ring ndash a
planar ring system with 4 nitrogen atoms surrounding a central metal atom (magnesium in the case of chlorophyll)
Two forms chlorophyll A and chlorophyll B In chlorophyll B an aldehyde side chain replaces a
methyl side chain When cooked plant cells release acids
Causes an H+ ion to replace magnesium atom in center of structure causing a color change to an olivebrown
Opens the possibility for photodegradation (breakdown by light)
Color
chlorophyll A
(replaced with an aldehyde in chlorophyll B)
Color Heme
Pigment found in red blood cells Structure is similar to chlorophyll but there is an iron
atom in the center of the porphyrin ring Found in the protein myoglobin responsible for
oxygen transport Bright red when bound to oxygen but slow process
of autoxidation converts iron from +2 to +3 changing color to brown (less desirable) (myoglobin metmyoglobin)
Color change can be prevented by vacuum packing or packing with an inert gas like CO2
Color
heme groupin myoglobin
Color Color in foods is a result of the structures seen in
anthocyanins carotenoids chlorophylls and hemes All of these structures include an extensive network of
delocalized pi-bonds Alternating single and double bonds is called a conjugated
system The greater the extent of pi bond delocalization the closer
together in energy bonding and antibonding orbitals become All molecules absorb light energy as it promotes e-s between
molecular orbitals (bonding and antibonding orbitals) ndash energy required is proportional to distance between orbitals (less distance = less energy)
As orbitals are close together in a conjugated system low energy light (in the visible region) is absorbed for e- promotion
Color in these groups is the product of visible light absorption - color we see is complementary to the color(s) absorbed
Molecules without an extensive delocalized pi bond network (conjugated system) lack color as orbitals are further apart and only higher energy light promotes e-s (ex the anthocyanin carbinol)
Color Some pigments are water soluble because the
structures contain a large amount of -OH groups (H-bonding) Anthocyanins
Some pigments are fat soluble (ie not water soluble) because their structures contain little or no -OH groups (no H-bonding) carotenoids
Color
Many synthetic dyes are biochemically active and could be potentially harmful
Short-term toxicity easy to test and categorize but long-term effects are more difficult to study
Use of dyes in foods must be regulated but regulations are not standardized internationally posing issues in trade
Color Cooking foods often leads to browning
Two processes responsible Maillard reactions ndash combination of sugars and
proteins Caramelization ndash dehydration of sugar
Both involve removal of water molecule(s)
Color Maillard reactions
Sugars and proteins within the food combine in a condensation reaction
Aldehyde group in sugar (O atom) combines with amino group in protein (2 H atoms)
Initial condensation products polymerize to form brown-colored melanoidins
Maillard reactions only happen gt 140deg C Rate depends on amino acid present (ex lysine
reacts faster than cysteine)
initialcondensationproduct
Color Caramelization
Happens in foods high in carbohydrates Sugars dehydrate (lose H2O) at high temperatures
leaving behind C (dark brown color)
Browning intensifies the longer food is cooked eventually burning it (pure carbon is black)
Rate depends on Sugar type (fructose in fruits caramelizes very quickly) pH ndash extremes (high and low) promote caramelization
Genetically Modified Foods
Produced when organisms with modified DNA are used in food production Used to
Provide pest or disease resistance Bt corn contains toxin from bacillis thuringiensis that kills
insect pests Fungal-resistant potatoes Nematode-resistant bananas (nematode = worm)
Improve quality and range of crop Development of higher-yielding rice varieties Development of corn that can grow in dryer environments
Produce medicines or other products in large quantities Use of chickens that have been modified to lay eggs
containing human interferon (combats tumors and viruses) Use of cows to produce milk rich in omega-3 fatty acids
(polyunsaturated fats essential to growth development brain function)
Moth larva
Genetically Modified Foods
Drawbacks Are GM foods safe Will GM food production alter the natural ecosystem Do we understand enough about genetic
modification GM foods
Can cause allergic reactions in some people Have a slightly different composition from natural foods ndash
alters diet Produce altered pollen ndash might escape and cross with natural
species Long-term effects might be catastrophic unknown so far
Texture Food texture is related to physical properties
Hardness Elasticity Viscosity
These properties can be altered by Cooking Use of dispersed systems
Dispersed system = a stabilized macroscopically homogeneous mixture of two immiscible phases
(this means two substances that would not ordinarily mix ldquoappear tordquo on a macroscopic level (although at the molecular level they are still separate)
Texture Many types of dispersed systems name depends on
the physical states of the substances mixed LiquidSolid or SolidLiquid
Solid particles suspended in a liquid is called a suspension
Ex Blood (blood cells suspended in plasma) Liquid dispersed throughout a solid medium is called a
gel Ex Fruit Jelly (water trapped in a solid protein matrix)
LiquidLiquid Stable blend of two liquids that donrsquot mix is called an
emulsion Ex Mayonaisse (oil droplets suspended in aqueous system)
LiquidGas or GasLiquid Gas bubbles trapped in liquid medium is called a foam
Ex Whipped cream or egg whites Liquid droplets suspended in gas are called aerosols
Ex Aromas from food carried through the air
Texture Dispersed systems will slowly separate over
time Separation can be slowed by adding emulsifiers
Emulsifiers are stabilizers used to keep immiscible substance together
Have surfactant capability (can bind to both substances in suspension)
Similar to micelles in the action of soaps
Ex Lecithin Found commonly in egg
yolks One end is highly charged
and water soluble (bonds toaqueous phase) the otheris not (bonds to non-aqueous phase)
Texture Lecithin in mayonnaise
Lecithin is the emulsifier Mayonnaise made by beating eggs with
vinegar and oil Lecithin is found in eggs ndash charged
hydrophilic end bonds well to vinegar uncharged hydrophobic end bonds to oil
Vigorous beating produces many small oil droplets maximizing surface area for lecithin to act on and produce a stable emulsion
Stabilizers like sodium phosphate or metals are added to prevent separation (chefs use metal bowls)
hydrophilic
hydrophobic
Stereochemistry in Food Many food-specific compounds have a chiral
carbon atom and thus exist as two different enantiomers (optical isomers) Optical isomers are mirror images of one another ldquoOptical activityrdquo refers to the fact that the two mirror
image isomers rotate the direction of plane-polarized light in opposite directions
Enantiomers that rotate polarized light in a clockwise direction are said to be dextrorotatory (dex-tro-rota-tory) and have a + rotational value (d +) ndash In Latin dexter means ldquoright siderdquo
Enantiomers that rotate polarized light in an anti-clockwise direction are said to be laevorotatory (lay-vo-rota-tory) and have a ndash rotational value (l -) ndash In Latin laevus means ldquoleft siderdquo
There are two systems used to provide specific names to each enantiomeric form
Stereochemistry in Food Older system used for naming sugars and amino
acids Enantiomeric forms are labeled ldquoLrdquo and ldquoDrdquo
Again Laevus for left and Dexter for right Based off a compound called glyceraldehyde
chiral carbon
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Nutrients (water and vitaminsminerals)
Do not provide energy Water is used for transport and
various metabolic processes Vitamins and minerals are also
important in metabolic processes and as enzyme cofactors
Fats and Oils
Properties of a fat (chiefly melting point and chemical stability) are related to The degree of unsaturation ( of double bonds in
the hydrocarbon chains) More double bonds = lower melting point and more
reactive Length of the hydrocarbon chains
Shorter chains = lower melting point Whether the chain is cis or trans isomerized
around double bonds cis = lower melting point
Fats and Oils Saturated ndash all C-C single bonds
Fatty acid has a regular zig-zag shape due to geometry around sp3 hybridized carbon atoms
Monounsaturated ndash one C=C double bond Can be cis or trans isomerized
cis means hydrogen atoms are on same side of double bond trans means hydogen atoms are on opposite sides of the
double bond Polyunsaturated ndash multiple C=C double bonds
Can be either cis or trans isomerized A ldquofatrdquo is a tryglyceride that is solid at room
temperature Usually saturated monounsaturated or trans unsaturated
An oil is a triglyceride that is liquid at room temperature Usually polyunsaturated
Fats and Oils Fats with longer hydrocarbon chains are able to make
more van der Waals forces between each other making molecules harder to separate Higher melting point
Saturated fats have ldquostraightrdquo chains that pack closely and allow for lots of contact between molecules making molecules harder to separate Higher melting point
Trans-unsaturated fats have straight chains just as saturated fats do Higher melting point
Cis-unsaturated fats have irregularly-shaped less ldquostraightrdquo chains Do not pack as closely molecules are easier to separate Lower melting point
Fats and Oils
Fats and Oils ldquoDegree of Crystallizationrdquo is
related to the melting point of a fat Higher melting point means a higher
degree of crystallization (fat is more likely to be solid at room temperature)
Increases with Increasing degree of saturation Increasing amount of trans-unsaturation Higher molecular mass
Naturally-occuring triglycerides most commonly tend to be cis-unsaturated
Fats and Oils cis-unsaturated fats are typically the
healthiest Lower melting point allows for less
buildup of plaque in the arteries that can cause stroke or heart attack
trans-unsaturated fats are less healthy do not commonly occur naturally are harder to metabolize and buildup in fatty tissue Cause an increase in LDL cholesterol
(Low Density Lipoprotein or ldquobadrdquo cholesterol
Fats and Oils Unsaturated oils are more reactive due to the
possibility of addition reactions across the double bonds Are thus less stable and keep less well than saturated
fats Prone to auto-oxidation in the presence of light
(photo-oxidation) which is a reaction of the fats with atmospheric oxygen
Also more prone to hydrogenation (addition of hydrogen) hydrolysis (breaking of the fat back into glycerol and fatty acids) and microbial degradation
Fats and Oils Unsaturated fats are often artificially
hydrogenatedpartially hydrogenated Increases degree of saturation
Allows for control of texture because melting point is affected
Improves stability and shelf life as reactivity is decreased Improves cooking technique where more solid fats are
needed Hydrogen gas is added over a solid nickel catalyst
Double bonds converted to single bonds and degree of saturation increases
Drawback - decreases the health value as fats are healthier when mono- or poly-unsaturated
Ni(s)
Shelf Life Foods gradually become unfit for consumption
due to Spoilage (growth of organisms) Changes in texture smell flavor or appearance
Undesirable processes caused by Change in water content Chemical reactions Exposure to light Changes in temperature
Shelf life is the length of time a product can be stored without these undesirable changes occurring
Shelf Life Change in water content
Causes texture change Loss of water increases exposure to air and thus oxidation
Causes rancidity and discoloration Increase in water encourages microbial growth and
spoilage Chemical reactionstemperature change
Increased temperature increases rates of ldquoharmful reactionsrdquo
Changes in pH or temperature affect the amount of water in a food
Souring with decrease in pH Changes color Can decrease nutritional value
Light provides energy for ldquoharmfulrdquo chemical reactions
Shelf Life Rancidity is a common type of food
degradation Unpleasant textures smells and flavors of fats
and oils
Two types of rancidity Hydrolytic rancidity ndash ester bond in fat is broken
yielding free fatty acids (reverse of formation of a fat) Oxidative rancidity ndash oxygen reacts near the C=C
double bonds in unsaturated fats
Shelf Life Hydrolytic rancidity of fats and oils
reverse of fat formation uses water (hydro lysis = ldquowaterrdquo ldquosplittingrdquo) to split triglycerides back into glycerol and fatty acids
Encouraged by Lipase ndash an enzyme produced by microorganisms Deep frying ndash encourages reaction of fats with moisture in
food Releases free fatty acids
4 ndash 8 carbon fatty acids have a powerfully pungent aromaflavor
palmitic stearic oleic lauric acids give a soapy fatty feel to foods
Shelf Life Oxidative rancidity of fats and oils
Reaction of atmospheric oxygen with fats and oils initiates complex process producing highly reactive free radicals
Products include unpleasant smellingtasting byproducts
More of an issue with increasing degree of unsaturation (more C=C double bonds to react with)
Encouraged by the presence of light (photo-oxidation) Enzymes produced by microorganisms
Shelf Life Oxidative rancidity of fats and oils occurs in 3
steps Initiation by exposure to light ndash produces highly
reactive hydrocarbon radicals (species with an unpaired electron)
R-H R + H Propagation ndash radicals produce other radicals
R + O2 R-O-O ROO + R-H R-O-O-H + R
Termination ndash radicals encounter one another and end the reaction
R + R R-R R-O-O + R-O-O R-O-O-O-O-R R + R-O-O R-O-O-R
(R-H = unsaturated fat or oil R = hydrocarbon radical images on next slide)
Shelf Life Initiation
Shelf Life Propagation
Shelf Life Termination
Shelf Life Shelf life is prolonged by hindering spoilage
processes Packaging
Opaque or darkened packages block light Can be gas impermeable to limit exposure to oxygen and water Can be filled with inert gases or vacuum packed (no gases)
Storage Low temperatures slow harmful reactions Smoking or drying foods removes water and hinder microbial
growth Additives
Salt or sugar added to remove water and hinder microbial growth
KNO3 or NaNO3 salts are reducing agents and can prevent harmful oxidation reactions
Anti-microbial agents Pickling - Organic acids and their salts (ex benzoic acid and
benzoate salts) make pH unfavorable for microbial growth Fermentation ndash production of alcohol hinders microbial growth
Shelf Life Antioxidants delay oxidative degradation
processes by reacting with oxygen to contain free radical formation Can occur naturally
Vitamin C (ascorbic acid) ndash citrus and green vegetables Vitamin E (tocopherol) ndash nuts seeds grains canola oil Beta-carotene ndash carrots broccoli tomatoes peaches Selenium ndash shellfish meat eggs grains Foods high in natural antioxidants green tea blueberries
cranberries dark chocolate turmeric oregano Can be synthetic additives but may have harmful
side effects BHA BHT PG THBP TBHQ
these are all based around a phenol
groupwhich is not
necessarily found in natural
antioxidants
(Full structures in
data booklet)
Shelf Life Types of antioxidants
Free radical quenchers React with radicals to produce less reactive radicals (HA =
quencher)R-O-O + HA R-O-O-H + A
Chelating agents Form very stable complex ions with transition metals (which
can produce radicals) Found naturally in rosemary tea and mustard Salts of the organic acid EDTA are added as artificial chelating
agents Reducing agents
React with oxygen or hydroperoxides Vitamin C or carotenoids are natural reducing agents
Color Foods are colored by either pigments or dyes
Pigments occur naturally Dyes are added artificially and must be tested for
safety Dyes or pigments will absorb a range of light
frequencies and reflect others The color we see in a dye or pigment is the result of
the colors of light reflected not absorbed Ex chlorophyll in green leaf vegetables absorbs red
and blue light reflecting green Molecular structures all involve extensive
delocalized pi bonding (shown on next slide) This system of delocalized pi bonding (conjugated
system) is responsible for the color we see
Color Some of the most common natural pigment
groups are Anthocyanins
Ex Cyanidin Carotenoids
Ex Beta-carotene Chlorophyll
Ex Chlorophyll-A Heme
Ex Heme B group
heme B groupchlorophyll-A
cyanidin
β-carotene
Color Anthocyanins
Responsible for reds pinks blues in berries beets flowers (Flavonones which give color to red grapes and berries are closely related to anthocyanins)
3-ring structures with varying numbers of OH groups in varying positions
Structure and therefore color is related to pH
predominantly red at low pH (acidic) blue at high pH (basic) and colorlesspale yellow at neutral pH
Temperature May break down at high temperatures and cause browning
Exposure to metal Form complexes with iron and aluminum and can change color
Color also affected when anthocyanins bond to sugars
Color Color of anthocyanins is pH dependent (they are
acidbase indicators)
Color Carotenes
Responsible for orange yellow and red colors in foods like carrots bananas tomatoes and saffron
Characterized by long hydrocarbon chains that often have carbon rings on the ends
Have nutritional value precursors to vitamin A (important in vision) act as antioxidants
Relatively stable during food processing but presence of C=C double bonds in hydrocarbon chain opens them up to oxidative degradation as seen in fats
Causes discoloration Prevents carotenoids from being able to be converted to
vitamin A
Color
β-carotene
Color Astaxanthin is a red pigment similar to
carotenoids found in lobster crab and salmon Bonds to proteins in the live animal and gives a
bluegreen color When heated bond to protein is broken which modifies
the structure and frequency of light absorbed appears bright red
Also an antioxidant
Color Chlorophyll
Green pigment responsible for plant photosynthesis Found in green vegetables Structure is centered around a porphyrin ring ndash a
planar ring system with 4 nitrogen atoms surrounding a central metal atom (magnesium in the case of chlorophyll)
Two forms chlorophyll A and chlorophyll B In chlorophyll B an aldehyde side chain replaces a
methyl side chain When cooked plant cells release acids
Causes an H+ ion to replace magnesium atom in center of structure causing a color change to an olivebrown
Opens the possibility for photodegradation (breakdown by light)
Color
chlorophyll A
(replaced with an aldehyde in chlorophyll B)
Color Heme
Pigment found in red blood cells Structure is similar to chlorophyll but there is an iron
atom in the center of the porphyrin ring Found in the protein myoglobin responsible for
oxygen transport Bright red when bound to oxygen but slow process
of autoxidation converts iron from +2 to +3 changing color to brown (less desirable) (myoglobin metmyoglobin)
Color change can be prevented by vacuum packing or packing with an inert gas like CO2
Color
heme groupin myoglobin
Color Color in foods is a result of the structures seen in
anthocyanins carotenoids chlorophylls and hemes All of these structures include an extensive network of
delocalized pi-bonds Alternating single and double bonds is called a conjugated
system The greater the extent of pi bond delocalization the closer
together in energy bonding and antibonding orbitals become All molecules absorb light energy as it promotes e-s between
molecular orbitals (bonding and antibonding orbitals) ndash energy required is proportional to distance between orbitals (less distance = less energy)
As orbitals are close together in a conjugated system low energy light (in the visible region) is absorbed for e- promotion
Color in these groups is the product of visible light absorption - color we see is complementary to the color(s) absorbed
Molecules without an extensive delocalized pi bond network (conjugated system) lack color as orbitals are further apart and only higher energy light promotes e-s (ex the anthocyanin carbinol)
Color Some pigments are water soluble because the
structures contain a large amount of -OH groups (H-bonding) Anthocyanins
Some pigments are fat soluble (ie not water soluble) because their structures contain little or no -OH groups (no H-bonding) carotenoids
Color
Many synthetic dyes are biochemically active and could be potentially harmful
Short-term toxicity easy to test and categorize but long-term effects are more difficult to study
Use of dyes in foods must be regulated but regulations are not standardized internationally posing issues in trade
Color Cooking foods often leads to browning
Two processes responsible Maillard reactions ndash combination of sugars and
proteins Caramelization ndash dehydration of sugar
Both involve removal of water molecule(s)
Color Maillard reactions
Sugars and proteins within the food combine in a condensation reaction
Aldehyde group in sugar (O atom) combines with amino group in protein (2 H atoms)
Initial condensation products polymerize to form brown-colored melanoidins
Maillard reactions only happen gt 140deg C Rate depends on amino acid present (ex lysine
reacts faster than cysteine)
initialcondensationproduct
Color Caramelization
Happens in foods high in carbohydrates Sugars dehydrate (lose H2O) at high temperatures
leaving behind C (dark brown color)
Browning intensifies the longer food is cooked eventually burning it (pure carbon is black)
Rate depends on Sugar type (fructose in fruits caramelizes very quickly) pH ndash extremes (high and low) promote caramelization
Genetically Modified Foods
Produced when organisms with modified DNA are used in food production Used to
Provide pest or disease resistance Bt corn contains toxin from bacillis thuringiensis that kills
insect pests Fungal-resistant potatoes Nematode-resistant bananas (nematode = worm)
Improve quality and range of crop Development of higher-yielding rice varieties Development of corn that can grow in dryer environments
Produce medicines or other products in large quantities Use of chickens that have been modified to lay eggs
containing human interferon (combats tumors and viruses) Use of cows to produce milk rich in omega-3 fatty acids
(polyunsaturated fats essential to growth development brain function)
Moth larva
Genetically Modified Foods
Drawbacks Are GM foods safe Will GM food production alter the natural ecosystem Do we understand enough about genetic
modification GM foods
Can cause allergic reactions in some people Have a slightly different composition from natural foods ndash
alters diet Produce altered pollen ndash might escape and cross with natural
species Long-term effects might be catastrophic unknown so far
Texture Food texture is related to physical properties
Hardness Elasticity Viscosity
These properties can be altered by Cooking Use of dispersed systems
Dispersed system = a stabilized macroscopically homogeneous mixture of two immiscible phases
(this means two substances that would not ordinarily mix ldquoappear tordquo on a macroscopic level (although at the molecular level they are still separate)
Texture Many types of dispersed systems name depends on
the physical states of the substances mixed LiquidSolid or SolidLiquid
Solid particles suspended in a liquid is called a suspension
Ex Blood (blood cells suspended in plasma) Liquid dispersed throughout a solid medium is called a
gel Ex Fruit Jelly (water trapped in a solid protein matrix)
LiquidLiquid Stable blend of two liquids that donrsquot mix is called an
emulsion Ex Mayonaisse (oil droplets suspended in aqueous system)
LiquidGas or GasLiquid Gas bubbles trapped in liquid medium is called a foam
Ex Whipped cream or egg whites Liquid droplets suspended in gas are called aerosols
Ex Aromas from food carried through the air
Texture Dispersed systems will slowly separate over
time Separation can be slowed by adding emulsifiers
Emulsifiers are stabilizers used to keep immiscible substance together
Have surfactant capability (can bind to both substances in suspension)
Similar to micelles in the action of soaps
Ex Lecithin Found commonly in egg
yolks One end is highly charged
and water soluble (bonds toaqueous phase) the otheris not (bonds to non-aqueous phase)
Texture Lecithin in mayonnaise
Lecithin is the emulsifier Mayonnaise made by beating eggs with
vinegar and oil Lecithin is found in eggs ndash charged
hydrophilic end bonds well to vinegar uncharged hydrophobic end bonds to oil
Vigorous beating produces many small oil droplets maximizing surface area for lecithin to act on and produce a stable emulsion
Stabilizers like sodium phosphate or metals are added to prevent separation (chefs use metal bowls)
hydrophilic
hydrophobic
Stereochemistry in Food Many food-specific compounds have a chiral
carbon atom and thus exist as two different enantiomers (optical isomers) Optical isomers are mirror images of one another ldquoOptical activityrdquo refers to the fact that the two mirror
image isomers rotate the direction of plane-polarized light in opposite directions
Enantiomers that rotate polarized light in a clockwise direction are said to be dextrorotatory (dex-tro-rota-tory) and have a + rotational value (d +) ndash In Latin dexter means ldquoright siderdquo
Enantiomers that rotate polarized light in an anti-clockwise direction are said to be laevorotatory (lay-vo-rota-tory) and have a ndash rotational value (l -) ndash In Latin laevus means ldquoleft siderdquo
There are two systems used to provide specific names to each enantiomeric form
Stereochemistry in Food Older system used for naming sugars and amino
acids Enantiomeric forms are labeled ldquoLrdquo and ldquoDrdquo
Again Laevus for left and Dexter for right Based off a compound called glyceraldehyde
chiral carbon
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Fats and Oils
Properties of a fat (chiefly melting point and chemical stability) are related to The degree of unsaturation ( of double bonds in
the hydrocarbon chains) More double bonds = lower melting point and more
reactive Length of the hydrocarbon chains
Shorter chains = lower melting point Whether the chain is cis or trans isomerized
around double bonds cis = lower melting point
Fats and Oils Saturated ndash all C-C single bonds
Fatty acid has a regular zig-zag shape due to geometry around sp3 hybridized carbon atoms
Monounsaturated ndash one C=C double bond Can be cis or trans isomerized
cis means hydrogen atoms are on same side of double bond trans means hydogen atoms are on opposite sides of the
double bond Polyunsaturated ndash multiple C=C double bonds
Can be either cis or trans isomerized A ldquofatrdquo is a tryglyceride that is solid at room
temperature Usually saturated monounsaturated or trans unsaturated
An oil is a triglyceride that is liquid at room temperature Usually polyunsaturated
Fats and Oils Fats with longer hydrocarbon chains are able to make
more van der Waals forces between each other making molecules harder to separate Higher melting point
Saturated fats have ldquostraightrdquo chains that pack closely and allow for lots of contact between molecules making molecules harder to separate Higher melting point
Trans-unsaturated fats have straight chains just as saturated fats do Higher melting point
Cis-unsaturated fats have irregularly-shaped less ldquostraightrdquo chains Do not pack as closely molecules are easier to separate Lower melting point
Fats and Oils
Fats and Oils ldquoDegree of Crystallizationrdquo is
related to the melting point of a fat Higher melting point means a higher
degree of crystallization (fat is more likely to be solid at room temperature)
Increases with Increasing degree of saturation Increasing amount of trans-unsaturation Higher molecular mass
Naturally-occuring triglycerides most commonly tend to be cis-unsaturated
Fats and Oils cis-unsaturated fats are typically the
healthiest Lower melting point allows for less
buildup of plaque in the arteries that can cause stroke or heart attack
trans-unsaturated fats are less healthy do not commonly occur naturally are harder to metabolize and buildup in fatty tissue Cause an increase in LDL cholesterol
(Low Density Lipoprotein or ldquobadrdquo cholesterol
Fats and Oils Unsaturated oils are more reactive due to the
possibility of addition reactions across the double bonds Are thus less stable and keep less well than saturated
fats Prone to auto-oxidation in the presence of light
(photo-oxidation) which is a reaction of the fats with atmospheric oxygen
Also more prone to hydrogenation (addition of hydrogen) hydrolysis (breaking of the fat back into glycerol and fatty acids) and microbial degradation
Fats and Oils Unsaturated fats are often artificially
hydrogenatedpartially hydrogenated Increases degree of saturation
Allows for control of texture because melting point is affected
Improves stability and shelf life as reactivity is decreased Improves cooking technique where more solid fats are
needed Hydrogen gas is added over a solid nickel catalyst
Double bonds converted to single bonds and degree of saturation increases
Drawback - decreases the health value as fats are healthier when mono- or poly-unsaturated
Ni(s)
Shelf Life Foods gradually become unfit for consumption
due to Spoilage (growth of organisms) Changes in texture smell flavor or appearance
Undesirable processes caused by Change in water content Chemical reactions Exposure to light Changes in temperature
Shelf life is the length of time a product can be stored without these undesirable changes occurring
Shelf Life Change in water content
Causes texture change Loss of water increases exposure to air and thus oxidation
Causes rancidity and discoloration Increase in water encourages microbial growth and
spoilage Chemical reactionstemperature change
Increased temperature increases rates of ldquoharmful reactionsrdquo
Changes in pH or temperature affect the amount of water in a food
Souring with decrease in pH Changes color Can decrease nutritional value
Light provides energy for ldquoharmfulrdquo chemical reactions
Shelf Life Rancidity is a common type of food
degradation Unpleasant textures smells and flavors of fats
and oils
Two types of rancidity Hydrolytic rancidity ndash ester bond in fat is broken
yielding free fatty acids (reverse of formation of a fat) Oxidative rancidity ndash oxygen reacts near the C=C
double bonds in unsaturated fats
Shelf Life Hydrolytic rancidity of fats and oils
reverse of fat formation uses water (hydro lysis = ldquowaterrdquo ldquosplittingrdquo) to split triglycerides back into glycerol and fatty acids
Encouraged by Lipase ndash an enzyme produced by microorganisms Deep frying ndash encourages reaction of fats with moisture in
food Releases free fatty acids
4 ndash 8 carbon fatty acids have a powerfully pungent aromaflavor
palmitic stearic oleic lauric acids give a soapy fatty feel to foods
Shelf Life Oxidative rancidity of fats and oils
Reaction of atmospheric oxygen with fats and oils initiates complex process producing highly reactive free radicals
Products include unpleasant smellingtasting byproducts
More of an issue with increasing degree of unsaturation (more C=C double bonds to react with)
Encouraged by the presence of light (photo-oxidation) Enzymes produced by microorganisms
Shelf Life Oxidative rancidity of fats and oils occurs in 3
steps Initiation by exposure to light ndash produces highly
reactive hydrocarbon radicals (species with an unpaired electron)
R-H R + H Propagation ndash radicals produce other radicals
R + O2 R-O-O ROO + R-H R-O-O-H + R
Termination ndash radicals encounter one another and end the reaction
R + R R-R R-O-O + R-O-O R-O-O-O-O-R R + R-O-O R-O-O-R
(R-H = unsaturated fat or oil R = hydrocarbon radical images on next slide)
Shelf Life Initiation
Shelf Life Propagation
Shelf Life Termination
Shelf Life Shelf life is prolonged by hindering spoilage
processes Packaging
Opaque or darkened packages block light Can be gas impermeable to limit exposure to oxygen and water Can be filled with inert gases or vacuum packed (no gases)
Storage Low temperatures slow harmful reactions Smoking or drying foods removes water and hinder microbial
growth Additives
Salt or sugar added to remove water and hinder microbial growth
KNO3 or NaNO3 salts are reducing agents and can prevent harmful oxidation reactions
Anti-microbial agents Pickling - Organic acids and their salts (ex benzoic acid and
benzoate salts) make pH unfavorable for microbial growth Fermentation ndash production of alcohol hinders microbial growth
Shelf Life Antioxidants delay oxidative degradation
processes by reacting with oxygen to contain free radical formation Can occur naturally
Vitamin C (ascorbic acid) ndash citrus and green vegetables Vitamin E (tocopherol) ndash nuts seeds grains canola oil Beta-carotene ndash carrots broccoli tomatoes peaches Selenium ndash shellfish meat eggs grains Foods high in natural antioxidants green tea blueberries
cranberries dark chocolate turmeric oregano Can be synthetic additives but may have harmful
side effects BHA BHT PG THBP TBHQ
these are all based around a phenol
groupwhich is not
necessarily found in natural
antioxidants
(Full structures in
data booklet)
Shelf Life Types of antioxidants
Free radical quenchers React with radicals to produce less reactive radicals (HA =
quencher)R-O-O + HA R-O-O-H + A
Chelating agents Form very stable complex ions with transition metals (which
can produce radicals) Found naturally in rosemary tea and mustard Salts of the organic acid EDTA are added as artificial chelating
agents Reducing agents
React with oxygen or hydroperoxides Vitamin C or carotenoids are natural reducing agents
Color Foods are colored by either pigments or dyes
Pigments occur naturally Dyes are added artificially and must be tested for
safety Dyes or pigments will absorb a range of light
frequencies and reflect others The color we see in a dye or pigment is the result of
the colors of light reflected not absorbed Ex chlorophyll in green leaf vegetables absorbs red
and blue light reflecting green Molecular structures all involve extensive
delocalized pi bonding (shown on next slide) This system of delocalized pi bonding (conjugated
system) is responsible for the color we see
Color Some of the most common natural pigment
groups are Anthocyanins
Ex Cyanidin Carotenoids
Ex Beta-carotene Chlorophyll
Ex Chlorophyll-A Heme
Ex Heme B group
heme B groupchlorophyll-A
cyanidin
β-carotene
Color Anthocyanins
Responsible for reds pinks blues in berries beets flowers (Flavonones which give color to red grapes and berries are closely related to anthocyanins)
3-ring structures with varying numbers of OH groups in varying positions
Structure and therefore color is related to pH
predominantly red at low pH (acidic) blue at high pH (basic) and colorlesspale yellow at neutral pH
Temperature May break down at high temperatures and cause browning
Exposure to metal Form complexes with iron and aluminum and can change color
Color also affected when anthocyanins bond to sugars
Color Color of anthocyanins is pH dependent (they are
acidbase indicators)
Color Carotenes
Responsible for orange yellow and red colors in foods like carrots bananas tomatoes and saffron
Characterized by long hydrocarbon chains that often have carbon rings on the ends
Have nutritional value precursors to vitamin A (important in vision) act as antioxidants
Relatively stable during food processing but presence of C=C double bonds in hydrocarbon chain opens them up to oxidative degradation as seen in fats
Causes discoloration Prevents carotenoids from being able to be converted to
vitamin A
Color
β-carotene
Color Astaxanthin is a red pigment similar to
carotenoids found in lobster crab and salmon Bonds to proteins in the live animal and gives a
bluegreen color When heated bond to protein is broken which modifies
the structure and frequency of light absorbed appears bright red
Also an antioxidant
Color Chlorophyll
Green pigment responsible for plant photosynthesis Found in green vegetables Structure is centered around a porphyrin ring ndash a
planar ring system with 4 nitrogen atoms surrounding a central metal atom (magnesium in the case of chlorophyll)
Two forms chlorophyll A and chlorophyll B In chlorophyll B an aldehyde side chain replaces a
methyl side chain When cooked plant cells release acids
Causes an H+ ion to replace magnesium atom in center of structure causing a color change to an olivebrown
Opens the possibility for photodegradation (breakdown by light)
Color
chlorophyll A
(replaced with an aldehyde in chlorophyll B)
Color Heme
Pigment found in red blood cells Structure is similar to chlorophyll but there is an iron
atom in the center of the porphyrin ring Found in the protein myoglobin responsible for
oxygen transport Bright red when bound to oxygen but slow process
of autoxidation converts iron from +2 to +3 changing color to brown (less desirable) (myoglobin metmyoglobin)
Color change can be prevented by vacuum packing or packing with an inert gas like CO2
Color
heme groupin myoglobin
Color Color in foods is a result of the structures seen in
anthocyanins carotenoids chlorophylls and hemes All of these structures include an extensive network of
delocalized pi-bonds Alternating single and double bonds is called a conjugated
system The greater the extent of pi bond delocalization the closer
together in energy bonding and antibonding orbitals become All molecules absorb light energy as it promotes e-s between
molecular orbitals (bonding and antibonding orbitals) ndash energy required is proportional to distance between orbitals (less distance = less energy)
As orbitals are close together in a conjugated system low energy light (in the visible region) is absorbed for e- promotion
Color in these groups is the product of visible light absorption - color we see is complementary to the color(s) absorbed
Molecules without an extensive delocalized pi bond network (conjugated system) lack color as orbitals are further apart and only higher energy light promotes e-s (ex the anthocyanin carbinol)
Color Some pigments are water soluble because the
structures contain a large amount of -OH groups (H-bonding) Anthocyanins
Some pigments are fat soluble (ie not water soluble) because their structures contain little or no -OH groups (no H-bonding) carotenoids
Color
Many synthetic dyes are biochemically active and could be potentially harmful
Short-term toxicity easy to test and categorize but long-term effects are more difficult to study
Use of dyes in foods must be regulated but regulations are not standardized internationally posing issues in trade
Color Cooking foods often leads to browning
Two processes responsible Maillard reactions ndash combination of sugars and
proteins Caramelization ndash dehydration of sugar
Both involve removal of water molecule(s)
Color Maillard reactions
Sugars and proteins within the food combine in a condensation reaction
Aldehyde group in sugar (O atom) combines with amino group in protein (2 H atoms)
Initial condensation products polymerize to form brown-colored melanoidins
Maillard reactions only happen gt 140deg C Rate depends on amino acid present (ex lysine
reacts faster than cysteine)
initialcondensationproduct
Color Caramelization
Happens in foods high in carbohydrates Sugars dehydrate (lose H2O) at high temperatures
leaving behind C (dark brown color)
Browning intensifies the longer food is cooked eventually burning it (pure carbon is black)
Rate depends on Sugar type (fructose in fruits caramelizes very quickly) pH ndash extremes (high and low) promote caramelization
Genetically Modified Foods
Produced when organisms with modified DNA are used in food production Used to
Provide pest or disease resistance Bt corn contains toxin from bacillis thuringiensis that kills
insect pests Fungal-resistant potatoes Nematode-resistant bananas (nematode = worm)
Improve quality and range of crop Development of higher-yielding rice varieties Development of corn that can grow in dryer environments
Produce medicines or other products in large quantities Use of chickens that have been modified to lay eggs
containing human interferon (combats tumors and viruses) Use of cows to produce milk rich in omega-3 fatty acids
(polyunsaturated fats essential to growth development brain function)
Moth larva
Genetically Modified Foods
Drawbacks Are GM foods safe Will GM food production alter the natural ecosystem Do we understand enough about genetic
modification GM foods
Can cause allergic reactions in some people Have a slightly different composition from natural foods ndash
alters diet Produce altered pollen ndash might escape and cross with natural
species Long-term effects might be catastrophic unknown so far
Texture Food texture is related to physical properties
Hardness Elasticity Viscosity
These properties can be altered by Cooking Use of dispersed systems
Dispersed system = a stabilized macroscopically homogeneous mixture of two immiscible phases
(this means two substances that would not ordinarily mix ldquoappear tordquo on a macroscopic level (although at the molecular level they are still separate)
Texture Many types of dispersed systems name depends on
the physical states of the substances mixed LiquidSolid or SolidLiquid
Solid particles suspended in a liquid is called a suspension
Ex Blood (blood cells suspended in plasma) Liquid dispersed throughout a solid medium is called a
gel Ex Fruit Jelly (water trapped in a solid protein matrix)
LiquidLiquid Stable blend of two liquids that donrsquot mix is called an
emulsion Ex Mayonaisse (oil droplets suspended in aqueous system)
LiquidGas or GasLiquid Gas bubbles trapped in liquid medium is called a foam
Ex Whipped cream or egg whites Liquid droplets suspended in gas are called aerosols
Ex Aromas from food carried through the air
Texture Dispersed systems will slowly separate over
time Separation can be slowed by adding emulsifiers
Emulsifiers are stabilizers used to keep immiscible substance together
Have surfactant capability (can bind to both substances in suspension)
Similar to micelles in the action of soaps
Ex Lecithin Found commonly in egg
yolks One end is highly charged
and water soluble (bonds toaqueous phase) the otheris not (bonds to non-aqueous phase)
Texture Lecithin in mayonnaise
Lecithin is the emulsifier Mayonnaise made by beating eggs with
vinegar and oil Lecithin is found in eggs ndash charged
hydrophilic end bonds well to vinegar uncharged hydrophobic end bonds to oil
Vigorous beating produces many small oil droplets maximizing surface area for lecithin to act on and produce a stable emulsion
Stabilizers like sodium phosphate or metals are added to prevent separation (chefs use metal bowls)
hydrophilic
hydrophobic
Stereochemistry in Food Many food-specific compounds have a chiral
carbon atom and thus exist as two different enantiomers (optical isomers) Optical isomers are mirror images of one another ldquoOptical activityrdquo refers to the fact that the two mirror
image isomers rotate the direction of plane-polarized light in opposite directions
Enantiomers that rotate polarized light in a clockwise direction are said to be dextrorotatory (dex-tro-rota-tory) and have a + rotational value (d +) ndash In Latin dexter means ldquoright siderdquo
Enantiomers that rotate polarized light in an anti-clockwise direction are said to be laevorotatory (lay-vo-rota-tory) and have a ndash rotational value (l -) ndash In Latin laevus means ldquoleft siderdquo
There are two systems used to provide specific names to each enantiomeric form
Stereochemistry in Food Older system used for naming sugars and amino
acids Enantiomeric forms are labeled ldquoLrdquo and ldquoDrdquo
Again Laevus for left and Dexter for right Based off a compound called glyceraldehyde
chiral carbon
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Fats and Oils Saturated ndash all C-C single bonds
Fatty acid has a regular zig-zag shape due to geometry around sp3 hybridized carbon atoms
Monounsaturated ndash one C=C double bond Can be cis or trans isomerized
cis means hydrogen atoms are on same side of double bond trans means hydogen atoms are on opposite sides of the
double bond Polyunsaturated ndash multiple C=C double bonds
Can be either cis or trans isomerized A ldquofatrdquo is a tryglyceride that is solid at room
temperature Usually saturated monounsaturated or trans unsaturated
An oil is a triglyceride that is liquid at room temperature Usually polyunsaturated
Fats and Oils Fats with longer hydrocarbon chains are able to make
more van der Waals forces between each other making molecules harder to separate Higher melting point
Saturated fats have ldquostraightrdquo chains that pack closely and allow for lots of contact between molecules making molecules harder to separate Higher melting point
Trans-unsaturated fats have straight chains just as saturated fats do Higher melting point
Cis-unsaturated fats have irregularly-shaped less ldquostraightrdquo chains Do not pack as closely molecules are easier to separate Lower melting point
Fats and Oils
Fats and Oils ldquoDegree of Crystallizationrdquo is
related to the melting point of a fat Higher melting point means a higher
degree of crystallization (fat is more likely to be solid at room temperature)
Increases with Increasing degree of saturation Increasing amount of trans-unsaturation Higher molecular mass
Naturally-occuring triglycerides most commonly tend to be cis-unsaturated
Fats and Oils cis-unsaturated fats are typically the
healthiest Lower melting point allows for less
buildup of plaque in the arteries that can cause stroke or heart attack
trans-unsaturated fats are less healthy do not commonly occur naturally are harder to metabolize and buildup in fatty tissue Cause an increase in LDL cholesterol
(Low Density Lipoprotein or ldquobadrdquo cholesterol
Fats and Oils Unsaturated oils are more reactive due to the
possibility of addition reactions across the double bonds Are thus less stable and keep less well than saturated
fats Prone to auto-oxidation in the presence of light
(photo-oxidation) which is a reaction of the fats with atmospheric oxygen
Also more prone to hydrogenation (addition of hydrogen) hydrolysis (breaking of the fat back into glycerol and fatty acids) and microbial degradation
Fats and Oils Unsaturated fats are often artificially
hydrogenatedpartially hydrogenated Increases degree of saturation
Allows for control of texture because melting point is affected
Improves stability and shelf life as reactivity is decreased Improves cooking technique where more solid fats are
needed Hydrogen gas is added over a solid nickel catalyst
Double bonds converted to single bonds and degree of saturation increases
Drawback - decreases the health value as fats are healthier when mono- or poly-unsaturated
Ni(s)
Shelf Life Foods gradually become unfit for consumption
due to Spoilage (growth of organisms) Changes in texture smell flavor or appearance
Undesirable processes caused by Change in water content Chemical reactions Exposure to light Changes in temperature
Shelf life is the length of time a product can be stored without these undesirable changes occurring
Shelf Life Change in water content
Causes texture change Loss of water increases exposure to air and thus oxidation
Causes rancidity and discoloration Increase in water encourages microbial growth and
spoilage Chemical reactionstemperature change
Increased temperature increases rates of ldquoharmful reactionsrdquo
Changes in pH or temperature affect the amount of water in a food
Souring with decrease in pH Changes color Can decrease nutritional value
Light provides energy for ldquoharmfulrdquo chemical reactions
Shelf Life Rancidity is a common type of food
degradation Unpleasant textures smells and flavors of fats
and oils
Two types of rancidity Hydrolytic rancidity ndash ester bond in fat is broken
yielding free fatty acids (reverse of formation of a fat) Oxidative rancidity ndash oxygen reacts near the C=C
double bonds in unsaturated fats
Shelf Life Hydrolytic rancidity of fats and oils
reverse of fat formation uses water (hydro lysis = ldquowaterrdquo ldquosplittingrdquo) to split triglycerides back into glycerol and fatty acids
Encouraged by Lipase ndash an enzyme produced by microorganisms Deep frying ndash encourages reaction of fats with moisture in
food Releases free fatty acids
4 ndash 8 carbon fatty acids have a powerfully pungent aromaflavor
palmitic stearic oleic lauric acids give a soapy fatty feel to foods
Shelf Life Oxidative rancidity of fats and oils
Reaction of atmospheric oxygen with fats and oils initiates complex process producing highly reactive free radicals
Products include unpleasant smellingtasting byproducts
More of an issue with increasing degree of unsaturation (more C=C double bonds to react with)
Encouraged by the presence of light (photo-oxidation) Enzymes produced by microorganisms
Shelf Life Oxidative rancidity of fats and oils occurs in 3
steps Initiation by exposure to light ndash produces highly
reactive hydrocarbon radicals (species with an unpaired electron)
R-H R + H Propagation ndash radicals produce other radicals
R + O2 R-O-O ROO + R-H R-O-O-H + R
Termination ndash radicals encounter one another and end the reaction
R + R R-R R-O-O + R-O-O R-O-O-O-O-R R + R-O-O R-O-O-R
(R-H = unsaturated fat or oil R = hydrocarbon radical images on next slide)
Shelf Life Initiation
Shelf Life Propagation
Shelf Life Termination
Shelf Life Shelf life is prolonged by hindering spoilage
processes Packaging
Opaque or darkened packages block light Can be gas impermeable to limit exposure to oxygen and water Can be filled with inert gases or vacuum packed (no gases)
Storage Low temperatures slow harmful reactions Smoking or drying foods removes water and hinder microbial
growth Additives
Salt or sugar added to remove water and hinder microbial growth
KNO3 or NaNO3 salts are reducing agents and can prevent harmful oxidation reactions
Anti-microbial agents Pickling - Organic acids and their salts (ex benzoic acid and
benzoate salts) make pH unfavorable for microbial growth Fermentation ndash production of alcohol hinders microbial growth
Shelf Life Antioxidants delay oxidative degradation
processes by reacting with oxygen to contain free radical formation Can occur naturally
Vitamin C (ascorbic acid) ndash citrus and green vegetables Vitamin E (tocopherol) ndash nuts seeds grains canola oil Beta-carotene ndash carrots broccoli tomatoes peaches Selenium ndash shellfish meat eggs grains Foods high in natural antioxidants green tea blueberries
cranberries dark chocolate turmeric oregano Can be synthetic additives but may have harmful
side effects BHA BHT PG THBP TBHQ
these are all based around a phenol
groupwhich is not
necessarily found in natural
antioxidants
(Full structures in
data booklet)
Shelf Life Types of antioxidants
Free radical quenchers React with radicals to produce less reactive radicals (HA =
quencher)R-O-O + HA R-O-O-H + A
Chelating agents Form very stable complex ions with transition metals (which
can produce radicals) Found naturally in rosemary tea and mustard Salts of the organic acid EDTA are added as artificial chelating
agents Reducing agents
React with oxygen or hydroperoxides Vitamin C or carotenoids are natural reducing agents
Color Foods are colored by either pigments or dyes
Pigments occur naturally Dyes are added artificially and must be tested for
safety Dyes or pigments will absorb a range of light
frequencies and reflect others The color we see in a dye or pigment is the result of
the colors of light reflected not absorbed Ex chlorophyll in green leaf vegetables absorbs red
and blue light reflecting green Molecular structures all involve extensive
delocalized pi bonding (shown on next slide) This system of delocalized pi bonding (conjugated
system) is responsible for the color we see
Color Some of the most common natural pigment
groups are Anthocyanins
Ex Cyanidin Carotenoids
Ex Beta-carotene Chlorophyll
Ex Chlorophyll-A Heme
Ex Heme B group
heme B groupchlorophyll-A
cyanidin
β-carotene
Color Anthocyanins
Responsible for reds pinks blues in berries beets flowers (Flavonones which give color to red grapes and berries are closely related to anthocyanins)
3-ring structures with varying numbers of OH groups in varying positions
Structure and therefore color is related to pH
predominantly red at low pH (acidic) blue at high pH (basic) and colorlesspale yellow at neutral pH
Temperature May break down at high temperatures and cause browning
Exposure to metal Form complexes with iron and aluminum and can change color
Color also affected when anthocyanins bond to sugars
Color Color of anthocyanins is pH dependent (they are
acidbase indicators)
Color Carotenes
Responsible for orange yellow and red colors in foods like carrots bananas tomatoes and saffron
Characterized by long hydrocarbon chains that often have carbon rings on the ends
Have nutritional value precursors to vitamin A (important in vision) act as antioxidants
Relatively stable during food processing but presence of C=C double bonds in hydrocarbon chain opens them up to oxidative degradation as seen in fats
Causes discoloration Prevents carotenoids from being able to be converted to
vitamin A
Color
β-carotene
Color Astaxanthin is a red pigment similar to
carotenoids found in lobster crab and salmon Bonds to proteins in the live animal and gives a
bluegreen color When heated bond to protein is broken which modifies
the structure and frequency of light absorbed appears bright red
Also an antioxidant
Color Chlorophyll
Green pigment responsible for plant photosynthesis Found in green vegetables Structure is centered around a porphyrin ring ndash a
planar ring system with 4 nitrogen atoms surrounding a central metal atom (magnesium in the case of chlorophyll)
Two forms chlorophyll A and chlorophyll B In chlorophyll B an aldehyde side chain replaces a
methyl side chain When cooked plant cells release acids
Causes an H+ ion to replace magnesium atom in center of structure causing a color change to an olivebrown
Opens the possibility for photodegradation (breakdown by light)
Color
chlorophyll A
(replaced with an aldehyde in chlorophyll B)
Color Heme
Pigment found in red blood cells Structure is similar to chlorophyll but there is an iron
atom in the center of the porphyrin ring Found in the protein myoglobin responsible for
oxygen transport Bright red when bound to oxygen but slow process
of autoxidation converts iron from +2 to +3 changing color to brown (less desirable) (myoglobin metmyoglobin)
Color change can be prevented by vacuum packing or packing with an inert gas like CO2
Color
heme groupin myoglobin
Color Color in foods is a result of the structures seen in
anthocyanins carotenoids chlorophylls and hemes All of these structures include an extensive network of
delocalized pi-bonds Alternating single and double bonds is called a conjugated
system The greater the extent of pi bond delocalization the closer
together in energy bonding and antibonding orbitals become All molecules absorb light energy as it promotes e-s between
molecular orbitals (bonding and antibonding orbitals) ndash energy required is proportional to distance between orbitals (less distance = less energy)
As orbitals are close together in a conjugated system low energy light (in the visible region) is absorbed for e- promotion
Color in these groups is the product of visible light absorption - color we see is complementary to the color(s) absorbed
Molecules without an extensive delocalized pi bond network (conjugated system) lack color as orbitals are further apart and only higher energy light promotes e-s (ex the anthocyanin carbinol)
Color Some pigments are water soluble because the
structures contain a large amount of -OH groups (H-bonding) Anthocyanins
Some pigments are fat soluble (ie not water soluble) because their structures contain little or no -OH groups (no H-bonding) carotenoids
Color
Many synthetic dyes are biochemically active and could be potentially harmful
Short-term toxicity easy to test and categorize but long-term effects are more difficult to study
Use of dyes in foods must be regulated but regulations are not standardized internationally posing issues in trade
Color Cooking foods often leads to browning
Two processes responsible Maillard reactions ndash combination of sugars and
proteins Caramelization ndash dehydration of sugar
Both involve removal of water molecule(s)
Color Maillard reactions
Sugars and proteins within the food combine in a condensation reaction
Aldehyde group in sugar (O atom) combines with amino group in protein (2 H atoms)
Initial condensation products polymerize to form brown-colored melanoidins
Maillard reactions only happen gt 140deg C Rate depends on amino acid present (ex lysine
reacts faster than cysteine)
initialcondensationproduct
Color Caramelization
Happens in foods high in carbohydrates Sugars dehydrate (lose H2O) at high temperatures
leaving behind C (dark brown color)
Browning intensifies the longer food is cooked eventually burning it (pure carbon is black)
Rate depends on Sugar type (fructose in fruits caramelizes very quickly) pH ndash extremes (high and low) promote caramelization
Genetically Modified Foods
Produced when organisms with modified DNA are used in food production Used to
Provide pest or disease resistance Bt corn contains toxin from bacillis thuringiensis that kills
insect pests Fungal-resistant potatoes Nematode-resistant bananas (nematode = worm)
Improve quality and range of crop Development of higher-yielding rice varieties Development of corn that can grow in dryer environments
Produce medicines or other products in large quantities Use of chickens that have been modified to lay eggs
containing human interferon (combats tumors and viruses) Use of cows to produce milk rich in omega-3 fatty acids
(polyunsaturated fats essential to growth development brain function)
Moth larva
Genetically Modified Foods
Drawbacks Are GM foods safe Will GM food production alter the natural ecosystem Do we understand enough about genetic
modification GM foods
Can cause allergic reactions in some people Have a slightly different composition from natural foods ndash
alters diet Produce altered pollen ndash might escape and cross with natural
species Long-term effects might be catastrophic unknown so far
Texture Food texture is related to physical properties
Hardness Elasticity Viscosity
These properties can be altered by Cooking Use of dispersed systems
Dispersed system = a stabilized macroscopically homogeneous mixture of two immiscible phases
(this means two substances that would not ordinarily mix ldquoappear tordquo on a macroscopic level (although at the molecular level they are still separate)
Texture Many types of dispersed systems name depends on
the physical states of the substances mixed LiquidSolid or SolidLiquid
Solid particles suspended in a liquid is called a suspension
Ex Blood (blood cells suspended in plasma) Liquid dispersed throughout a solid medium is called a
gel Ex Fruit Jelly (water trapped in a solid protein matrix)
LiquidLiquid Stable blend of two liquids that donrsquot mix is called an
emulsion Ex Mayonaisse (oil droplets suspended in aqueous system)
LiquidGas or GasLiquid Gas bubbles trapped in liquid medium is called a foam
Ex Whipped cream or egg whites Liquid droplets suspended in gas are called aerosols
Ex Aromas from food carried through the air
Texture Dispersed systems will slowly separate over
time Separation can be slowed by adding emulsifiers
Emulsifiers are stabilizers used to keep immiscible substance together
Have surfactant capability (can bind to both substances in suspension)
Similar to micelles in the action of soaps
Ex Lecithin Found commonly in egg
yolks One end is highly charged
and water soluble (bonds toaqueous phase) the otheris not (bonds to non-aqueous phase)
Texture Lecithin in mayonnaise
Lecithin is the emulsifier Mayonnaise made by beating eggs with
vinegar and oil Lecithin is found in eggs ndash charged
hydrophilic end bonds well to vinegar uncharged hydrophobic end bonds to oil
Vigorous beating produces many small oil droplets maximizing surface area for lecithin to act on and produce a stable emulsion
Stabilizers like sodium phosphate or metals are added to prevent separation (chefs use metal bowls)
hydrophilic
hydrophobic
Stereochemistry in Food Many food-specific compounds have a chiral
carbon atom and thus exist as two different enantiomers (optical isomers) Optical isomers are mirror images of one another ldquoOptical activityrdquo refers to the fact that the two mirror
image isomers rotate the direction of plane-polarized light in opposite directions
Enantiomers that rotate polarized light in a clockwise direction are said to be dextrorotatory (dex-tro-rota-tory) and have a + rotational value (d +) ndash In Latin dexter means ldquoright siderdquo
Enantiomers that rotate polarized light in an anti-clockwise direction are said to be laevorotatory (lay-vo-rota-tory) and have a ndash rotational value (l -) ndash In Latin laevus means ldquoleft siderdquo
There are two systems used to provide specific names to each enantiomeric form
Stereochemistry in Food Older system used for naming sugars and amino
acids Enantiomeric forms are labeled ldquoLrdquo and ldquoDrdquo
Again Laevus for left and Dexter for right Based off a compound called glyceraldehyde
chiral carbon
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Fats and Oils Fats with longer hydrocarbon chains are able to make
more van der Waals forces between each other making molecules harder to separate Higher melting point
Saturated fats have ldquostraightrdquo chains that pack closely and allow for lots of contact between molecules making molecules harder to separate Higher melting point
Trans-unsaturated fats have straight chains just as saturated fats do Higher melting point
Cis-unsaturated fats have irregularly-shaped less ldquostraightrdquo chains Do not pack as closely molecules are easier to separate Lower melting point
Fats and Oils
Fats and Oils ldquoDegree of Crystallizationrdquo is
related to the melting point of a fat Higher melting point means a higher
degree of crystallization (fat is more likely to be solid at room temperature)
Increases with Increasing degree of saturation Increasing amount of trans-unsaturation Higher molecular mass
Naturally-occuring triglycerides most commonly tend to be cis-unsaturated
Fats and Oils cis-unsaturated fats are typically the
healthiest Lower melting point allows for less
buildup of plaque in the arteries that can cause stroke or heart attack
trans-unsaturated fats are less healthy do not commonly occur naturally are harder to metabolize and buildup in fatty tissue Cause an increase in LDL cholesterol
(Low Density Lipoprotein or ldquobadrdquo cholesterol
Fats and Oils Unsaturated oils are more reactive due to the
possibility of addition reactions across the double bonds Are thus less stable and keep less well than saturated
fats Prone to auto-oxidation in the presence of light
(photo-oxidation) which is a reaction of the fats with atmospheric oxygen
Also more prone to hydrogenation (addition of hydrogen) hydrolysis (breaking of the fat back into glycerol and fatty acids) and microbial degradation
Fats and Oils Unsaturated fats are often artificially
hydrogenatedpartially hydrogenated Increases degree of saturation
Allows for control of texture because melting point is affected
Improves stability and shelf life as reactivity is decreased Improves cooking technique where more solid fats are
needed Hydrogen gas is added over a solid nickel catalyst
Double bonds converted to single bonds and degree of saturation increases
Drawback - decreases the health value as fats are healthier when mono- or poly-unsaturated
Ni(s)
Shelf Life Foods gradually become unfit for consumption
due to Spoilage (growth of organisms) Changes in texture smell flavor or appearance
Undesirable processes caused by Change in water content Chemical reactions Exposure to light Changes in temperature
Shelf life is the length of time a product can be stored without these undesirable changes occurring
Shelf Life Change in water content
Causes texture change Loss of water increases exposure to air and thus oxidation
Causes rancidity and discoloration Increase in water encourages microbial growth and
spoilage Chemical reactionstemperature change
Increased temperature increases rates of ldquoharmful reactionsrdquo
Changes in pH or temperature affect the amount of water in a food
Souring with decrease in pH Changes color Can decrease nutritional value
Light provides energy for ldquoharmfulrdquo chemical reactions
Shelf Life Rancidity is a common type of food
degradation Unpleasant textures smells and flavors of fats
and oils
Two types of rancidity Hydrolytic rancidity ndash ester bond in fat is broken
yielding free fatty acids (reverse of formation of a fat) Oxidative rancidity ndash oxygen reacts near the C=C
double bonds in unsaturated fats
Shelf Life Hydrolytic rancidity of fats and oils
reverse of fat formation uses water (hydro lysis = ldquowaterrdquo ldquosplittingrdquo) to split triglycerides back into glycerol and fatty acids
Encouraged by Lipase ndash an enzyme produced by microorganisms Deep frying ndash encourages reaction of fats with moisture in
food Releases free fatty acids
4 ndash 8 carbon fatty acids have a powerfully pungent aromaflavor
palmitic stearic oleic lauric acids give a soapy fatty feel to foods
Shelf Life Oxidative rancidity of fats and oils
Reaction of atmospheric oxygen with fats and oils initiates complex process producing highly reactive free radicals
Products include unpleasant smellingtasting byproducts
More of an issue with increasing degree of unsaturation (more C=C double bonds to react with)
Encouraged by the presence of light (photo-oxidation) Enzymes produced by microorganisms
Shelf Life Oxidative rancidity of fats and oils occurs in 3
steps Initiation by exposure to light ndash produces highly
reactive hydrocarbon radicals (species with an unpaired electron)
R-H R + H Propagation ndash radicals produce other radicals
R + O2 R-O-O ROO + R-H R-O-O-H + R
Termination ndash radicals encounter one another and end the reaction
R + R R-R R-O-O + R-O-O R-O-O-O-O-R R + R-O-O R-O-O-R
(R-H = unsaturated fat or oil R = hydrocarbon radical images on next slide)
Shelf Life Initiation
Shelf Life Propagation
Shelf Life Termination
Shelf Life Shelf life is prolonged by hindering spoilage
processes Packaging
Opaque or darkened packages block light Can be gas impermeable to limit exposure to oxygen and water Can be filled with inert gases or vacuum packed (no gases)
Storage Low temperatures slow harmful reactions Smoking or drying foods removes water and hinder microbial
growth Additives
Salt or sugar added to remove water and hinder microbial growth
KNO3 or NaNO3 salts are reducing agents and can prevent harmful oxidation reactions
Anti-microbial agents Pickling - Organic acids and their salts (ex benzoic acid and
benzoate salts) make pH unfavorable for microbial growth Fermentation ndash production of alcohol hinders microbial growth
Shelf Life Antioxidants delay oxidative degradation
processes by reacting with oxygen to contain free radical formation Can occur naturally
Vitamin C (ascorbic acid) ndash citrus and green vegetables Vitamin E (tocopherol) ndash nuts seeds grains canola oil Beta-carotene ndash carrots broccoli tomatoes peaches Selenium ndash shellfish meat eggs grains Foods high in natural antioxidants green tea blueberries
cranberries dark chocolate turmeric oregano Can be synthetic additives but may have harmful
side effects BHA BHT PG THBP TBHQ
these are all based around a phenol
groupwhich is not
necessarily found in natural
antioxidants
(Full structures in
data booklet)
Shelf Life Types of antioxidants
Free radical quenchers React with radicals to produce less reactive radicals (HA =
quencher)R-O-O + HA R-O-O-H + A
Chelating agents Form very stable complex ions with transition metals (which
can produce radicals) Found naturally in rosemary tea and mustard Salts of the organic acid EDTA are added as artificial chelating
agents Reducing agents
React with oxygen or hydroperoxides Vitamin C or carotenoids are natural reducing agents
Color Foods are colored by either pigments or dyes
Pigments occur naturally Dyes are added artificially and must be tested for
safety Dyes or pigments will absorb a range of light
frequencies and reflect others The color we see in a dye or pigment is the result of
the colors of light reflected not absorbed Ex chlorophyll in green leaf vegetables absorbs red
and blue light reflecting green Molecular structures all involve extensive
delocalized pi bonding (shown on next slide) This system of delocalized pi bonding (conjugated
system) is responsible for the color we see
Color Some of the most common natural pigment
groups are Anthocyanins
Ex Cyanidin Carotenoids
Ex Beta-carotene Chlorophyll
Ex Chlorophyll-A Heme
Ex Heme B group
heme B groupchlorophyll-A
cyanidin
β-carotene
Color Anthocyanins
Responsible for reds pinks blues in berries beets flowers (Flavonones which give color to red grapes and berries are closely related to anthocyanins)
3-ring structures with varying numbers of OH groups in varying positions
Structure and therefore color is related to pH
predominantly red at low pH (acidic) blue at high pH (basic) and colorlesspale yellow at neutral pH
Temperature May break down at high temperatures and cause browning
Exposure to metal Form complexes with iron and aluminum and can change color
Color also affected when anthocyanins bond to sugars
Color Color of anthocyanins is pH dependent (they are
acidbase indicators)
Color Carotenes
Responsible for orange yellow and red colors in foods like carrots bananas tomatoes and saffron
Characterized by long hydrocarbon chains that often have carbon rings on the ends
Have nutritional value precursors to vitamin A (important in vision) act as antioxidants
Relatively stable during food processing but presence of C=C double bonds in hydrocarbon chain opens them up to oxidative degradation as seen in fats
Causes discoloration Prevents carotenoids from being able to be converted to
vitamin A
Color
β-carotene
Color Astaxanthin is a red pigment similar to
carotenoids found in lobster crab and salmon Bonds to proteins in the live animal and gives a
bluegreen color When heated bond to protein is broken which modifies
the structure and frequency of light absorbed appears bright red
Also an antioxidant
Color Chlorophyll
Green pigment responsible for plant photosynthesis Found in green vegetables Structure is centered around a porphyrin ring ndash a
planar ring system with 4 nitrogen atoms surrounding a central metal atom (magnesium in the case of chlorophyll)
Two forms chlorophyll A and chlorophyll B In chlorophyll B an aldehyde side chain replaces a
methyl side chain When cooked plant cells release acids
Causes an H+ ion to replace magnesium atom in center of structure causing a color change to an olivebrown
Opens the possibility for photodegradation (breakdown by light)
Color
chlorophyll A
(replaced with an aldehyde in chlorophyll B)
Color Heme
Pigment found in red blood cells Structure is similar to chlorophyll but there is an iron
atom in the center of the porphyrin ring Found in the protein myoglobin responsible for
oxygen transport Bright red when bound to oxygen but slow process
of autoxidation converts iron from +2 to +3 changing color to brown (less desirable) (myoglobin metmyoglobin)
Color change can be prevented by vacuum packing or packing with an inert gas like CO2
Color
heme groupin myoglobin
Color Color in foods is a result of the structures seen in
anthocyanins carotenoids chlorophylls and hemes All of these structures include an extensive network of
delocalized pi-bonds Alternating single and double bonds is called a conjugated
system The greater the extent of pi bond delocalization the closer
together in energy bonding and antibonding orbitals become All molecules absorb light energy as it promotes e-s between
molecular orbitals (bonding and antibonding orbitals) ndash energy required is proportional to distance between orbitals (less distance = less energy)
As orbitals are close together in a conjugated system low energy light (in the visible region) is absorbed for e- promotion
Color in these groups is the product of visible light absorption - color we see is complementary to the color(s) absorbed
Molecules without an extensive delocalized pi bond network (conjugated system) lack color as orbitals are further apart and only higher energy light promotes e-s (ex the anthocyanin carbinol)
Color Some pigments are water soluble because the
structures contain a large amount of -OH groups (H-bonding) Anthocyanins
Some pigments are fat soluble (ie not water soluble) because their structures contain little or no -OH groups (no H-bonding) carotenoids
Color
Many synthetic dyes are biochemically active and could be potentially harmful
Short-term toxicity easy to test and categorize but long-term effects are more difficult to study
Use of dyes in foods must be regulated but regulations are not standardized internationally posing issues in trade
Color Cooking foods often leads to browning
Two processes responsible Maillard reactions ndash combination of sugars and
proteins Caramelization ndash dehydration of sugar
Both involve removal of water molecule(s)
Color Maillard reactions
Sugars and proteins within the food combine in a condensation reaction
Aldehyde group in sugar (O atom) combines with amino group in protein (2 H atoms)
Initial condensation products polymerize to form brown-colored melanoidins
Maillard reactions only happen gt 140deg C Rate depends on amino acid present (ex lysine
reacts faster than cysteine)
initialcondensationproduct
Color Caramelization
Happens in foods high in carbohydrates Sugars dehydrate (lose H2O) at high temperatures
leaving behind C (dark brown color)
Browning intensifies the longer food is cooked eventually burning it (pure carbon is black)
Rate depends on Sugar type (fructose in fruits caramelizes very quickly) pH ndash extremes (high and low) promote caramelization
Genetically Modified Foods
Produced when organisms with modified DNA are used in food production Used to
Provide pest or disease resistance Bt corn contains toxin from bacillis thuringiensis that kills
insect pests Fungal-resistant potatoes Nematode-resistant bananas (nematode = worm)
Improve quality and range of crop Development of higher-yielding rice varieties Development of corn that can grow in dryer environments
Produce medicines or other products in large quantities Use of chickens that have been modified to lay eggs
containing human interferon (combats tumors and viruses) Use of cows to produce milk rich in omega-3 fatty acids
(polyunsaturated fats essential to growth development brain function)
Moth larva
Genetically Modified Foods
Drawbacks Are GM foods safe Will GM food production alter the natural ecosystem Do we understand enough about genetic
modification GM foods
Can cause allergic reactions in some people Have a slightly different composition from natural foods ndash
alters diet Produce altered pollen ndash might escape and cross with natural
species Long-term effects might be catastrophic unknown so far
Texture Food texture is related to physical properties
Hardness Elasticity Viscosity
These properties can be altered by Cooking Use of dispersed systems
Dispersed system = a stabilized macroscopically homogeneous mixture of two immiscible phases
(this means two substances that would not ordinarily mix ldquoappear tordquo on a macroscopic level (although at the molecular level they are still separate)
Texture Many types of dispersed systems name depends on
the physical states of the substances mixed LiquidSolid or SolidLiquid
Solid particles suspended in a liquid is called a suspension
Ex Blood (blood cells suspended in plasma) Liquid dispersed throughout a solid medium is called a
gel Ex Fruit Jelly (water trapped in a solid protein matrix)
LiquidLiquid Stable blend of two liquids that donrsquot mix is called an
emulsion Ex Mayonaisse (oil droplets suspended in aqueous system)
LiquidGas or GasLiquid Gas bubbles trapped in liquid medium is called a foam
Ex Whipped cream or egg whites Liquid droplets suspended in gas are called aerosols
Ex Aromas from food carried through the air
Texture Dispersed systems will slowly separate over
time Separation can be slowed by adding emulsifiers
Emulsifiers are stabilizers used to keep immiscible substance together
Have surfactant capability (can bind to both substances in suspension)
Similar to micelles in the action of soaps
Ex Lecithin Found commonly in egg
yolks One end is highly charged
and water soluble (bonds toaqueous phase) the otheris not (bonds to non-aqueous phase)
Texture Lecithin in mayonnaise
Lecithin is the emulsifier Mayonnaise made by beating eggs with
vinegar and oil Lecithin is found in eggs ndash charged
hydrophilic end bonds well to vinegar uncharged hydrophobic end bonds to oil
Vigorous beating produces many small oil droplets maximizing surface area for lecithin to act on and produce a stable emulsion
Stabilizers like sodium phosphate or metals are added to prevent separation (chefs use metal bowls)
hydrophilic
hydrophobic
Stereochemistry in Food Many food-specific compounds have a chiral
carbon atom and thus exist as two different enantiomers (optical isomers) Optical isomers are mirror images of one another ldquoOptical activityrdquo refers to the fact that the two mirror
image isomers rotate the direction of plane-polarized light in opposite directions
Enantiomers that rotate polarized light in a clockwise direction are said to be dextrorotatory (dex-tro-rota-tory) and have a + rotational value (d +) ndash In Latin dexter means ldquoright siderdquo
Enantiomers that rotate polarized light in an anti-clockwise direction are said to be laevorotatory (lay-vo-rota-tory) and have a ndash rotational value (l -) ndash In Latin laevus means ldquoleft siderdquo
There are two systems used to provide specific names to each enantiomeric form
Stereochemistry in Food Older system used for naming sugars and amino
acids Enantiomeric forms are labeled ldquoLrdquo and ldquoDrdquo
Again Laevus for left and Dexter for right Based off a compound called glyceraldehyde
chiral carbon
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Fats and Oils
Fats and Oils ldquoDegree of Crystallizationrdquo is
related to the melting point of a fat Higher melting point means a higher
degree of crystallization (fat is more likely to be solid at room temperature)
Increases with Increasing degree of saturation Increasing amount of trans-unsaturation Higher molecular mass
Naturally-occuring triglycerides most commonly tend to be cis-unsaturated
Fats and Oils cis-unsaturated fats are typically the
healthiest Lower melting point allows for less
buildup of plaque in the arteries that can cause stroke or heart attack
trans-unsaturated fats are less healthy do not commonly occur naturally are harder to metabolize and buildup in fatty tissue Cause an increase in LDL cholesterol
(Low Density Lipoprotein or ldquobadrdquo cholesterol
Fats and Oils Unsaturated oils are more reactive due to the
possibility of addition reactions across the double bonds Are thus less stable and keep less well than saturated
fats Prone to auto-oxidation in the presence of light
(photo-oxidation) which is a reaction of the fats with atmospheric oxygen
Also more prone to hydrogenation (addition of hydrogen) hydrolysis (breaking of the fat back into glycerol and fatty acids) and microbial degradation
Fats and Oils Unsaturated fats are often artificially
hydrogenatedpartially hydrogenated Increases degree of saturation
Allows for control of texture because melting point is affected
Improves stability and shelf life as reactivity is decreased Improves cooking technique where more solid fats are
needed Hydrogen gas is added over a solid nickel catalyst
Double bonds converted to single bonds and degree of saturation increases
Drawback - decreases the health value as fats are healthier when mono- or poly-unsaturated
Ni(s)
Shelf Life Foods gradually become unfit for consumption
due to Spoilage (growth of organisms) Changes in texture smell flavor or appearance
Undesirable processes caused by Change in water content Chemical reactions Exposure to light Changes in temperature
Shelf life is the length of time a product can be stored without these undesirable changes occurring
Shelf Life Change in water content
Causes texture change Loss of water increases exposure to air and thus oxidation
Causes rancidity and discoloration Increase in water encourages microbial growth and
spoilage Chemical reactionstemperature change
Increased temperature increases rates of ldquoharmful reactionsrdquo
Changes in pH or temperature affect the amount of water in a food
Souring with decrease in pH Changes color Can decrease nutritional value
Light provides energy for ldquoharmfulrdquo chemical reactions
Shelf Life Rancidity is a common type of food
degradation Unpleasant textures smells and flavors of fats
and oils
Two types of rancidity Hydrolytic rancidity ndash ester bond in fat is broken
yielding free fatty acids (reverse of formation of a fat) Oxidative rancidity ndash oxygen reacts near the C=C
double bonds in unsaturated fats
Shelf Life Hydrolytic rancidity of fats and oils
reverse of fat formation uses water (hydro lysis = ldquowaterrdquo ldquosplittingrdquo) to split triglycerides back into glycerol and fatty acids
Encouraged by Lipase ndash an enzyme produced by microorganisms Deep frying ndash encourages reaction of fats with moisture in
food Releases free fatty acids
4 ndash 8 carbon fatty acids have a powerfully pungent aromaflavor
palmitic stearic oleic lauric acids give a soapy fatty feel to foods
Shelf Life Oxidative rancidity of fats and oils
Reaction of atmospheric oxygen with fats and oils initiates complex process producing highly reactive free radicals
Products include unpleasant smellingtasting byproducts
More of an issue with increasing degree of unsaturation (more C=C double bonds to react with)
Encouraged by the presence of light (photo-oxidation) Enzymes produced by microorganisms
Shelf Life Oxidative rancidity of fats and oils occurs in 3
steps Initiation by exposure to light ndash produces highly
reactive hydrocarbon radicals (species with an unpaired electron)
R-H R + H Propagation ndash radicals produce other radicals
R + O2 R-O-O ROO + R-H R-O-O-H + R
Termination ndash radicals encounter one another and end the reaction
R + R R-R R-O-O + R-O-O R-O-O-O-O-R R + R-O-O R-O-O-R
(R-H = unsaturated fat or oil R = hydrocarbon radical images on next slide)
Shelf Life Initiation
Shelf Life Propagation
Shelf Life Termination
Shelf Life Shelf life is prolonged by hindering spoilage
processes Packaging
Opaque or darkened packages block light Can be gas impermeable to limit exposure to oxygen and water Can be filled with inert gases or vacuum packed (no gases)
Storage Low temperatures slow harmful reactions Smoking or drying foods removes water and hinder microbial
growth Additives
Salt or sugar added to remove water and hinder microbial growth
KNO3 or NaNO3 salts are reducing agents and can prevent harmful oxidation reactions
Anti-microbial agents Pickling - Organic acids and their salts (ex benzoic acid and
benzoate salts) make pH unfavorable for microbial growth Fermentation ndash production of alcohol hinders microbial growth
Shelf Life Antioxidants delay oxidative degradation
processes by reacting with oxygen to contain free radical formation Can occur naturally
Vitamin C (ascorbic acid) ndash citrus and green vegetables Vitamin E (tocopherol) ndash nuts seeds grains canola oil Beta-carotene ndash carrots broccoli tomatoes peaches Selenium ndash shellfish meat eggs grains Foods high in natural antioxidants green tea blueberries
cranberries dark chocolate turmeric oregano Can be synthetic additives but may have harmful
side effects BHA BHT PG THBP TBHQ
these are all based around a phenol
groupwhich is not
necessarily found in natural
antioxidants
(Full structures in
data booklet)
Shelf Life Types of antioxidants
Free radical quenchers React with radicals to produce less reactive radicals (HA =
quencher)R-O-O + HA R-O-O-H + A
Chelating agents Form very stable complex ions with transition metals (which
can produce radicals) Found naturally in rosemary tea and mustard Salts of the organic acid EDTA are added as artificial chelating
agents Reducing agents
React with oxygen or hydroperoxides Vitamin C or carotenoids are natural reducing agents
Color Foods are colored by either pigments or dyes
Pigments occur naturally Dyes are added artificially and must be tested for
safety Dyes or pigments will absorb a range of light
frequencies and reflect others The color we see in a dye or pigment is the result of
the colors of light reflected not absorbed Ex chlorophyll in green leaf vegetables absorbs red
and blue light reflecting green Molecular structures all involve extensive
delocalized pi bonding (shown on next slide) This system of delocalized pi bonding (conjugated
system) is responsible for the color we see
Color Some of the most common natural pigment
groups are Anthocyanins
Ex Cyanidin Carotenoids
Ex Beta-carotene Chlorophyll
Ex Chlorophyll-A Heme
Ex Heme B group
heme B groupchlorophyll-A
cyanidin
β-carotene
Color Anthocyanins
Responsible for reds pinks blues in berries beets flowers (Flavonones which give color to red grapes and berries are closely related to anthocyanins)
3-ring structures with varying numbers of OH groups in varying positions
Structure and therefore color is related to pH
predominantly red at low pH (acidic) blue at high pH (basic) and colorlesspale yellow at neutral pH
Temperature May break down at high temperatures and cause browning
Exposure to metal Form complexes with iron and aluminum and can change color
Color also affected when anthocyanins bond to sugars
Color Color of anthocyanins is pH dependent (they are
acidbase indicators)
Color Carotenes
Responsible for orange yellow and red colors in foods like carrots bananas tomatoes and saffron
Characterized by long hydrocarbon chains that often have carbon rings on the ends
Have nutritional value precursors to vitamin A (important in vision) act as antioxidants
Relatively stable during food processing but presence of C=C double bonds in hydrocarbon chain opens them up to oxidative degradation as seen in fats
Causes discoloration Prevents carotenoids from being able to be converted to
vitamin A
Color
β-carotene
Color Astaxanthin is a red pigment similar to
carotenoids found in lobster crab and salmon Bonds to proteins in the live animal and gives a
bluegreen color When heated bond to protein is broken which modifies
the structure and frequency of light absorbed appears bright red
Also an antioxidant
Color Chlorophyll
Green pigment responsible for plant photosynthesis Found in green vegetables Structure is centered around a porphyrin ring ndash a
planar ring system with 4 nitrogen atoms surrounding a central metal atom (magnesium in the case of chlorophyll)
Two forms chlorophyll A and chlorophyll B In chlorophyll B an aldehyde side chain replaces a
methyl side chain When cooked plant cells release acids
Causes an H+ ion to replace magnesium atom in center of structure causing a color change to an olivebrown
Opens the possibility for photodegradation (breakdown by light)
Color
chlorophyll A
(replaced with an aldehyde in chlorophyll B)
Color Heme
Pigment found in red blood cells Structure is similar to chlorophyll but there is an iron
atom in the center of the porphyrin ring Found in the protein myoglobin responsible for
oxygen transport Bright red when bound to oxygen but slow process
of autoxidation converts iron from +2 to +3 changing color to brown (less desirable) (myoglobin metmyoglobin)
Color change can be prevented by vacuum packing or packing with an inert gas like CO2
Color
heme groupin myoglobin
Color Color in foods is a result of the structures seen in
anthocyanins carotenoids chlorophylls and hemes All of these structures include an extensive network of
delocalized pi-bonds Alternating single and double bonds is called a conjugated
system The greater the extent of pi bond delocalization the closer
together in energy bonding and antibonding orbitals become All molecules absorb light energy as it promotes e-s between
molecular orbitals (bonding and antibonding orbitals) ndash energy required is proportional to distance between orbitals (less distance = less energy)
As orbitals are close together in a conjugated system low energy light (in the visible region) is absorbed for e- promotion
Color in these groups is the product of visible light absorption - color we see is complementary to the color(s) absorbed
Molecules without an extensive delocalized pi bond network (conjugated system) lack color as orbitals are further apart and only higher energy light promotes e-s (ex the anthocyanin carbinol)
Color Some pigments are water soluble because the
structures contain a large amount of -OH groups (H-bonding) Anthocyanins
Some pigments are fat soluble (ie not water soluble) because their structures contain little or no -OH groups (no H-bonding) carotenoids
Color
Many synthetic dyes are biochemically active and could be potentially harmful
Short-term toxicity easy to test and categorize but long-term effects are more difficult to study
Use of dyes in foods must be regulated but regulations are not standardized internationally posing issues in trade
Color Cooking foods often leads to browning
Two processes responsible Maillard reactions ndash combination of sugars and
proteins Caramelization ndash dehydration of sugar
Both involve removal of water molecule(s)
Color Maillard reactions
Sugars and proteins within the food combine in a condensation reaction
Aldehyde group in sugar (O atom) combines with amino group in protein (2 H atoms)
Initial condensation products polymerize to form brown-colored melanoidins
Maillard reactions only happen gt 140deg C Rate depends on amino acid present (ex lysine
reacts faster than cysteine)
initialcondensationproduct
Color Caramelization
Happens in foods high in carbohydrates Sugars dehydrate (lose H2O) at high temperatures
leaving behind C (dark brown color)
Browning intensifies the longer food is cooked eventually burning it (pure carbon is black)
Rate depends on Sugar type (fructose in fruits caramelizes very quickly) pH ndash extremes (high and low) promote caramelization
Genetically Modified Foods
Produced when organisms with modified DNA are used in food production Used to
Provide pest or disease resistance Bt corn contains toxin from bacillis thuringiensis that kills
insect pests Fungal-resistant potatoes Nematode-resistant bananas (nematode = worm)
Improve quality and range of crop Development of higher-yielding rice varieties Development of corn that can grow in dryer environments
Produce medicines or other products in large quantities Use of chickens that have been modified to lay eggs
containing human interferon (combats tumors and viruses) Use of cows to produce milk rich in omega-3 fatty acids
(polyunsaturated fats essential to growth development brain function)
Moth larva
Genetically Modified Foods
Drawbacks Are GM foods safe Will GM food production alter the natural ecosystem Do we understand enough about genetic
modification GM foods
Can cause allergic reactions in some people Have a slightly different composition from natural foods ndash
alters diet Produce altered pollen ndash might escape and cross with natural
species Long-term effects might be catastrophic unknown so far
Texture Food texture is related to physical properties
Hardness Elasticity Viscosity
These properties can be altered by Cooking Use of dispersed systems
Dispersed system = a stabilized macroscopically homogeneous mixture of two immiscible phases
(this means two substances that would not ordinarily mix ldquoappear tordquo on a macroscopic level (although at the molecular level they are still separate)
Texture Many types of dispersed systems name depends on
the physical states of the substances mixed LiquidSolid or SolidLiquid
Solid particles suspended in a liquid is called a suspension
Ex Blood (blood cells suspended in plasma) Liquid dispersed throughout a solid medium is called a
gel Ex Fruit Jelly (water trapped in a solid protein matrix)
LiquidLiquid Stable blend of two liquids that donrsquot mix is called an
emulsion Ex Mayonaisse (oil droplets suspended in aqueous system)
LiquidGas or GasLiquid Gas bubbles trapped in liquid medium is called a foam
Ex Whipped cream or egg whites Liquid droplets suspended in gas are called aerosols
Ex Aromas from food carried through the air
Texture Dispersed systems will slowly separate over
time Separation can be slowed by adding emulsifiers
Emulsifiers are stabilizers used to keep immiscible substance together
Have surfactant capability (can bind to both substances in suspension)
Similar to micelles in the action of soaps
Ex Lecithin Found commonly in egg
yolks One end is highly charged
and water soluble (bonds toaqueous phase) the otheris not (bonds to non-aqueous phase)
Texture Lecithin in mayonnaise
Lecithin is the emulsifier Mayonnaise made by beating eggs with
vinegar and oil Lecithin is found in eggs ndash charged
hydrophilic end bonds well to vinegar uncharged hydrophobic end bonds to oil
Vigorous beating produces many small oil droplets maximizing surface area for lecithin to act on and produce a stable emulsion
Stabilizers like sodium phosphate or metals are added to prevent separation (chefs use metal bowls)
hydrophilic
hydrophobic
Stereochemistry in Food Many food-specific compounds have a chiral
carbon atom and thus exist as two different enantiomers (optical isomers) Optical isomers are mirror images of one another ldquoOptical activityrdquo refers to the fact that the two mirror
image isomers rotate the direction of plane-polarized light in opposite directions
Enantiomers that rotate polarized light in a clockwise direction are said to be dextrorotatory (dex-tro-rota-tory) and have a + rotational value (d +) ndash In Latin dexter means ldquoright siderdquo
Enantiomers that rotate polarized light in an anti-clockwise direction are said to be laevorotatory (lay-vo-rota-tory) and have a ndash rotational value (l -) ndash In Latin laevus means ldquoleft siderdquo
There are two systems used to provide specific names to each enantiomeric form
Stereochemistry in Food Older system used for naming sugars and amino
acids Enantiomeric forms are labeled ldquoLrdquo and ldquoDrdquo
Again Laevus for left and Dexter for right Based off a compound called glyceraldehyde
chiral carbon
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Fats and Oils ldquoDegree of Crystallizationrdquo is
related to the melting point of a fat Higher melting point means a higher
degree of crystallization (fat is more likely to be solid at room temperature)
Increases with Increasing degree of saturation Increasing amount of trans-unsaturation Higher molecular mass
Naturally-occuring triglycerides most commonly tend to be cis-unsaturated
Fats and Oils cis-unsaturated fats are typically the
healthiest Lower melting point allows for less
buildup of plaque in the arteries that can cause stroke or heart attack
trans-unsaturated fats are less healthy do not commonly occur naturally are harder to metabolize and buildup in fatty tissue Cause an increase in LDL cholesterol
(Low Density Lipoprotein or ldquobadrdquo cholesterol
Fats and Oils Unsaturated oils are more reactive due to the
possibility of addition reactions across the double bonds Are thus less stable and keep less well than saturated
fats Prone to auto-oxidation in the presence of light
(photo-oxidation) which is a reaction of the fats with atmospheric oxygen
Also more prone to hydrogenation (addition of hydrogen) hydrolysis (breaking of the fat back into glycerol and fatty acids) and microbial degradation
Fats and Oils Unsaturated fats are often artificially
hydrogenatedpartially hydrogenated Increases degree of saturation
Allows for control of texture because melting point is affected
Improves stability and shelf life as reactivity is decreased Improves cooking technique where more solid fats are
needed Hydrogen gas is added over a solid nickel catalyst
Double bonds converted to single bonds and degree of saturation increases
Drawback - decreases the health value as fats are healthier when mono- or poly-unsaturated
Ni(s)
Shelf Life Foods gradually become unfit for consumption
due to Spoilage (growth of organisms) Changes in texture smell flavor or appearance
Undesirable processes caused by Change in water content Chemical reactions Exposure to light Changes in temperature
Shelf life is the length of time a product can be stored without these undesirable changes occurring
Shelf Life Change in water content
Causes texture change Loss of water increases exposure to air and thus oxidation
Causes rancidity and discoloration Increase in water encourages microbial growth and
spoilage Chemical reactionstemperature change
Increased temperature increases rates of ldquoharmful reactionsrdquo
Changes in pH or temperature affect the amount of water in a food
Souring with decrease in pH Changes color Can decrease nutritional value
Light provides energy for ldquoharmfulrdquo chemical reactions
Shelf Life Rancidity is a common type of food
degradation Unpleasant textures smells and flavors of fats
and oils
Two types of rancidity Hydrolytic rancidity ndash ester bond in fat is broken
yielding free fatty acids (reverse of formation of a fat) Oxidative rancidity ndash oxygen reacts near the C=C
double bonds in unsaturated fats
Shelf Life Hydrolytic rancidity of fats and oils
reverse of fat formation uses water (hydro lysis = ldquowaterrdquo ldquosplittingrdquo) to split triglycerides back into glycerol and fatty acids
Encouraged by Lipase ndash an enzyme produced by microorganisms Deep frying ndash encourages reaction of fats with moisture in
food Releases free fatty acids
4 ndash 8 carbon fatty acids have a powerfully pungent aromaflavor
palmitic stearic oleic lauric acids give a soapy fatty feel to foods
Shelf Life Oxidative rancidity of fats and oils
Reaction of atmospheric oxygen with fats and oils initiates complex process producing highly reactive free radicals
Products include unpleasant smellingtasting byproducts
More of an issue with increasing degree of unsaturation (more C=C double bonds to react with)
Encouraged by the presence of light (photo-oxidation) Enzymes produced by microorganisms
Shelf Life Oxidative rancidity of fats and oils occurs in 3
steps Initiation by exposure to light ndash produces highly
reactive hydrocarbon radicals (species with an unpaired electron)
R-H R + H Propagation ndash radicals produce other radicals
R + O2 R-O-O ROO + R-H R-O-O-H + R
Termination ndash radicals encounter one another and end the reaction
R + R R-R R-O-O + R-O-O R-O-O-O-O-R R + R-O-O R-O-O-R
(R-H = unsaturated fat or oil R = hydrocarbon radical images on next slide)
Shelf Life Initiation
Shelf Life Propagation
Shelf Life Termination
Shelf Life Shelf life is prolonged by hindering spoilage
processes Packaging
Opaque or darkened packages block light Can be gas impermeable to limit exposure to oxygen and water Can be filled with inert gases or vacuum packed (no gases)
Storage Low temperatures slow harmful reactions Smoking or drying foods removes water and hinder microbial
growth Additives
Salt or sugar added to remove water and hinder microbial growth
KNO3 or NaNO3 salts are reducing agents and can prevent harmful oxidation reactions
Anti-microbial agents Pickling - Organic acids and their salts (ex benzoic acid and
benzoate salts) make pH unfavorable for microbial growth Fermentation ndash production of alcohol hinders microbial growth
Shelf Life Antioxidants delay oxidative degradation
processes by reacting with oxygen to contain free radical formation Can occur naturally
Vitamin C (ascorbic acid) ndash citrus and green vegetables Vitamin E (tocopherol) ndash nuts seeds grains canola oil Beta-carotene ndash carrots broccoli tomatoes peaches Selenium ndash shellfish meat eggs grains Foods high in natural antioxidants green tea blueberries
cranberries dark chocolate turmeric oregano Can be synthetic additives but may have harmful
side effects BHA BHT PG THBP TBHQ
these are all based around a phenol
groupwhich is not
necessarily found in natural
antioxidants
(Full structures in
data booklet)
Shelf Life Types of antioxidants
Free radical quenchers React with radicals to produce less reactive radicals (HA =
quencher)R-O-O + HA R-O-O-H + A
Chelating agents Form very stable complex ions with transition metals (which
can produce radicals) Found naturally in rosemary tea and mustard Salts of the organic acid EDTA are added as artificial chelating
agents Reducing agents
React with oxygen or hydroperoxides Vitamin C or carotenoids are natural reducing agents
Color Foods are colored by either pigments or dyes
Pigments occur naturally Dyes are added artificially and must be tested for
safety Dyes or pigments will absorb a range of light
frequencies and reflect others The color we see in a dye or pigment is the result of
the colors of light reflected not absorbed Ex chlorophyll in green leaf vegetables absorbs red
and blue light reflecting green Molecular structures all involve extensive
delocalized pi bonding (shown on next slide) This system of delocalized pi bonding (conjugated
system) is responsible for the color we see
Color Some of the most common natural pigment
groups are Anthocyanins
Ex Cyanidin Carotenoids
Ex Beta-carotene Chlorophyll
Ex Chlorophyll-A Heme
Ex Heme B group
heme B groupchlorophyll-A
cyanidin
β-carotene
Color Anthocyanins
Responsible for reds pinks blues in berries beets flowers (Flavonones which give color to red grapes and berries are closely related to anthocyanins)
3-ring structures with varying numbers of OH groups in varying positions
Structure and therefore color is related to pH
predominantly red at low pH (acidic) blue at high pH (basic) and colorlesspale yellow at neutral pH
Temperature May break down at high temperatures and cause browning
Exposure to metal Form complexes with iron and aluminum and can change color
Color also affected when anthocyanins bond to sugars
Color Color of anthocyanins is pH dependent (they are
acidbase indicators)
Color Carotenes
Responsible for orange yellow and red colors in foods like carrots bananas tomatoes and saffron
Characterized by long hydrocarbon chains that often have carbon rings on the ends
Have nutritional value precursors to vitamin A (important in vision) act as antioxidants
Relatively stable during food processing but presence of C=C double bonds in hydrocarbon chain opens them up to oxidative degradation as seen in fats
Causes discoloration Prevents carotenoids from being able to be converted to
vitamin A
Color
β-carotene
Color Astaxanthin is a red pigment similar to
carotenoids found in lobster crab and salmon Bonds to proteins in the live animal and gives a
bluegreen color When heated bond to protein is broken which modifies
the structure and frequency of light absorbed appears bright red
Also an antioxidant
Color Chlorophyll
Green pigment responsible for plant photosynthesis Found in green vegetables Structure is centered around a porphyrin ring ndash a
planar ring system with 4 nitrogen atoms surrounding a central metal atom (magnesium in the case of chlorophyll)
Two forms chlorophyll A and chlorophyll B In chlorophyll B an aldehyde side chain replaces a
methyl side chain When cooked plant cells release acids
Causes an H+ ion to replace magnesium atom in center of structure causing a color change to an olivebrown
Opens the possibility for photodegradation (breakdown by light)
Color
chlorophyll A
(replaced with an aldehyde in chlorophyll B)
Color Heme
Pigment found in red blood cells Structure is similar to chlorophyll but there is an iron
atom in the center of the porphyrin ring Found in the protein myoglobin responsible for
oxygen transport Bright red when bound to oxygen but slow process
of autoxidation converts iron from +2 to +3 changing color to brown (less desirable) (myoglobin metmyoglobin)
Color change can be prevented by vacuum packing or packing with an inert gas like CO2
Color
heme groupin myoglobin
Color Color in foods is a result of the structures seen in
anthocyanins carotenoids chlorophylls and hemes All of these structures include an extensive network of
delocalized pi-bonds Alternating single and double bonds is called a conjugated
system The greater the extent of pi bond delocalization the closer
together in energy bonding and antibonding orbitals become All molecules absorb light energy as it promotes e-s between
molecular orbitals (bonding and antibonding orbitals) ndash energy required is proportional to distance between orbitals (less distance = less energy)
As orbitals are close together in a conjugated system low energy light (in the visible region) is absorbed for e- promotion
Color in these groups is the product of visible light absorption - color we see is complementary to the color(s) absorbed
Molecules without an extensive delocalized pi bond network (conjugated system) lack color as orbitals are further apart and only higher energy light promotes e-s (ex the anthocyanin carbinol)
Color Some pigments are water soluble because the
structures contain a large amount of -OH groups (H-bonding) Anthocyanins
Some pigments are fat soluble (ie not water soluble) because their structures contain little or no -OH groups (no H-bonding) carotenoids
Color
Many synthetic dyes are biochemically active and could be potentially harmful
Short-term toxicity easy to test and categorize but long-term effects are more difficult to study
Use of dyes in foods must be regulated but regulations are not standardized internationally posing issues in trade
Color Cooking foods often leads to browning
Two processes responsible Maillard reactions ndash combination of sugars and
proteins Caramelization ndash dehydration of sugar
Both involve removal of water molecule(s)
Color Maillard reactions
Sugars and proteins within the food combine in a condensation reaction
Aldehyde group in sugar (O atom) combines with amino group in protein (2 H atoms)
Initial condensation products polymerize to form brown-colored melanoidins
Maillard reactions only happen gt 140deg C Rate depends on amino acid present (ex lysine
reacts faster than cysteine)
initialcondensationproduct
Color Caramelization
Happens in foods high in carbohydrates Sugars dehydrate (lose H2O) at high temperatures
leaving behind C (dark brown color)
Browning intensifies the longer food is cooked eventually burning it (pure carbon is black)
Rate depends on Sugar type (fructose in fruits caramelizes very quickly) pH ndash extremes (high and low) promote caramelization
Genetically Modified Foods
Produced when organisms with modified DNA are used in food production Used to
Provide pest or disease resistance Bt corn contains toxin from bacillis thuringiensis that kills
insect pests Fungal-resistant potatoes Nematode-resistant bananas (nematode = worm)
Improve quality and range of crop Development of higher-yielding rice varieties Development of corn that can grow in dryer environments
Produce medicines or other products in large quantities Use of chickens that have been modified to lay eggs
containing human interferon (combats tumors and viruses) Use of cows to produce milk rich in omega-3 fatty acids
(polyunsaturated fats essential to growth development brain function)
Moth larva
Genetically Modified Foods
Drawbacks Are GM foods safe Will GM food production alter the natural ecosystem Do we understand enough about genetic
modification GM foods
Can cause allergic reactions in some people Have a slightly different composition from natural foods ndash
alters diet Produce altered pollen ndash might escape and cross with natural
species Long-term effects might be catastrophic unknown so far
Texture Food texture is related to physical properties
Hardness Elasticity Viscosity
These properties can be altered by Cooking Use of dispersed systems
Dispersed system = a stabilized macroscopically homogeneous mixture of two immiscible phases
(this means two substances that would not ordinarily mix ldquoappear tordquo on a macroscopic level (although at the molecular level they are still separate)
Texture Many types of dispersed systems name depends on
the physical states of the substances mixed LiquidSolid or SolidLiquid
Solid particles suspended in a liquid is called a suspension
Ex Blood (blood cells suspended in plasma) Liquid dispersed throughout a solid medium is called a
gel Ex Fruit Jelly (water trapped in a solid protein matrix)
LiquidLiquid Stable blend of two liquids that donrsquot mix is called an
emulsion Ex Mayonaisse (oil droplets suspended in aqueous system)
LiquidGas or GasLiquid Gas bubbles trapped in liquid medium is called a foam
Ex Whipped cream or egg whites Liquid droplets suspended in gas are called aerosols
Ex Aromas from food carried through the air
Texture Dispersed systems will slowly separate over
time Separation can be slowed by adding emulsifiers
Emulsifiers are stabilizers used to keep immiscible substance together
Have surfactant capability (can bind to both substances in suspension)
Similar to micelles in the action of soaps
Ex Lecithin Found commonly in egg
yolks One end is highly charged
and water soluble (bonds toaqueous phase) the otheris not (bonds to non-aqueous phase)
Texture Lecithin in mayonnaise
Lecithin is the emulsifier Mayonnaise made by beating eggs with
vinegar and oil Lecithin is found in eggs ndash charged
hydrophilic end bonds well to vinegar uncharged hydrophobic end bonds to oil
Vigorous beating produces many small oil droplets maximizing surface area for lecithin to act on and produce a stable emulsion
Stabilizers like sodium phosphate or metals are added to prevent separation (chefs use metal bowls)
hydrophilic
hydrophobic
Stereochemistry in Food Many food-specific compounds have a chiral
carbon atom and thus exist as two different enantiomers (optical isomers) Optical isomers are mirror images of one another ldquoOptical activityrdquo refers to the fact that the two mirror
image isomers rotate the direction of plane-polarized light in opposite directions
Enantiomers that rotate polarized light in a clockwise direction are said to be dextrorotatory (dex-tro-rota-tory) and have a + rotational value (d +) ndash In Latin dexter means ldquoright siderdquo
Enantiomers that rotate polarized light in an anti-clockwise direction are said to be laevorotatory (lay-vo-rota-tory) and have a ndash rotational value (l -) ndash In Latin laevus means ldquoleft siderdquo
There are two systems used to provide specific names to each enantiomeric form
Stereochemistry in Food Older system used for naming sugars and amino
acids Enantiomeric forms are labeled ldquoLrdquo and ldquoDrdquo
Again Laevus for left and Dexter for right Based off a compound called glyceraldehyde
chiral carbon
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Fats and Oils cis-unsaturated fats are typically the
healthiest Lower melting point allows for less
buildup of plaque in the arteries that can cause stroke or heart attack
trans-unsaturated fats are less healthy do not commonly occur naturally are harder to metabolize and buildup in fatty tissue Cause an increase in LDL cholesterol
(Low Density Lipoprotein or ldquobadrdquo cholesterol
Fats and Oils Unsaturated oils are more reactive due to the
possibility of addition reactions across the double bonds Are thus less stable and keep less well than saturated
fats Prone to auto-oxidation in the presence of light
(photo-oxidation) which is a reaction of the fats with atmospheric oxygen
Also more prone to hydrogenation (addition of hydrogen) hydrolysis (breaking of the fat back into glycerol and fatty acids) and microbial degradation
Fats and Oils Unsaturated fats are often artificially
hydrogenatedpartially hydrogenated Increases degree of saturation
Allows for control of texture because melting point is affected
Improves stability and shelf life as reactivity is decreased Improves cooking technique where more solid fats are
needed Hydrogen gas is added over a solid nickel catalyst
Double bonds converted to single bonds and degree of saturation increases
Drawback - decreases the health value as fats are healthier when mono- or poly-unsaturated
Ni(s)
Shelf Life Foods gradually become unfit for consumption
due to Spoilage (growth of organisms) Changes in texture smell flavor or appearance
Undesirable processes caused by Change in water content Chemical reactions Exposure to light Changes in temperature
Shelf life is the length of time a product can be stored without these undesirable changes occurring
Shelf Life Change in water content
Causes texture change Loss of water increases exposure to air and thus oxidation
Causes rancidity and discoloration Increase in water encourages microbial growth and
spoilage Chemical reactionstemperature change
Increased temperature increases rates of ldquoharmful reactionsrdquo
Changes in pH or temperature affect the amount of water in a food
Souring with decrease in pH Changes color Can decrease nutritional value
Light provides energy for ldquoharmfulrdquo chemical reactions
Shelf Life Rancidity is a common type of food
degradation Unpleasant textures smells and flavors of fats
and oils
Two types of rancidity Hydrolytic rancidity ndash ester bond in fat is broken
yielding free fatty acids (reverse of formation of a fat) Oxidative rancidity ndash oxygen reacts near the C=C
double bonds in unsaturated fats
Shelf Life Hydrolytic rancidity of fats and oils
reverse of fat formation uses water (hydro lysis = ldquowaterrdquo ldquosplittingrdquo) to split triglycerides back into glycerol and fatty acids
Encouraged by Lipase ndash an enzyme produced by microorganisms Deep frying ndash encourages reaction of fats with moisture in
food Releases free fatty acids
4 ndash 8 carbon fatty acids have a powerfully pungent aromaflavor
palmitic stearic oleic lauric acids give a soapy fatty feel to foods
Shelf Life Oxidative rancidity of fats and oils
Reaction of atmospheric oxygen with fats and oils initiates complex process producing highly reactive free radicals
Products include unpleasant smellingtasting byproducts
More of an issue with increasing degree of unsaturation (more C=C double bonds to react with)
Encouraged by the presence of light (photo-oxidation) Enzymes produced by microorganisms
Shelf Life Oxidative rancidity of fats and oils occurs in 3
steps Initiation by exposure to light ndash produces highly
reactive hydrocarbon radicals (species with an unpaired electron)
R-H R + H Propagation ndash radicals produce other radicals
R + O2 R-O-O ROO + R-H R-O-O-H + R
Termination ndash radicals encounter one another and end the reaction
R + R R-R R-O-O + R-O-O R-O-O-O-O-R R + R-O-O R-O-O-R
(R-H = unsaturated fat or oil R = hydrocarbon radical images on next slide)
Shelf Life Initiation
Shelf Life Propagation
Shelf Life Termination
Shelf Life Shelf life is prolonged by hindering spoilage
processes Packaging
Opaque or darkened packages block light Can be gas impermeable to limit exposure to oxygen and water Can be filled with inert gases or vacuum packed (no gases)
Storage Low temperatures slow harmful reactions Smoking or drying foods removes water and hinder microbial
growth Additives
Salt or sugar added to remove water and hinder microbial growth
KNO3 or NaNO3 salts are reducing agents and can prevent harmful oxidation reactions
Anti-microbial agents Pickling - Organic acids and their salts (ex benzoic acid and
benzoate salts) make pH unfavorable for microbial growth Fermentation ndash production of alcohol hinders microbial growth
Shelf Life Antioxidants delay oxidative degradation
processes by reacting with oxygen to contain free radical formation Can occur naturally
Vitamin C (ascorbic acid) ndash citrus and green vegetables Vitamin E (tocopherol) ndash nuts seeds grains canola oil Beta-carotene ndash carrots broccoli tomatoes peaches Selenium ndash shellfish meat eggs grains Foods high in natural antioxidants green tea blueberries
cranberries dark chocolate turmeric oregano Can be synthetic additives but may have harmful
side effects BHA BHT PG THBP TBHQ
these are all based around a phenol
groupwhich is not
necessarily found in natural
antioxidants
(Full structures in
data booklet)
Shelf Life Types of antioxidants
Free radical quenchers React with radicals to produce less reactive radicals (HA =
quencher)R-O-O + HA R-O-O-H + A
Chelating agents Form very stable complex ions with transition metals (which
can produce radicals) Found naturally in rosemary tea and mustard Salts of the organic acid EDTA are added as artificial chelating
agents Reducing agents
React with oxygen or hydroperoxides Vitamin C or carotenoids are natural reducing agents
Color Foods are colored by either pigments or dyes
Pigments occur naturally Dyes are added artificially and must be tested for
safety Dyes or pigments will absorb a range of light
frequencies and reflect others The color we see in a dye or pigment is the result of
the colors of light reflected not absorbed Ex chlorophyll in green leaf vegetables absorbs red
and blue light reflecting green Molecular structures all involve extensive
delocalized pi bonding (shown on next slide) This system of delocalized pi bonding (conjugated
system) is responsible for the color we see
Color Some of the most common natural pigment
groups are Anthocyanins
Ex Cyanidin Carotenoids
Ex Beta-carotene Chlorophyll
Ex Chlorophyll-A Heme
Ex Heme B group
heme B groupchlorophyll-A
cyanidin
β-carotene
Color Anthocyanins
Responsible for reds pinks blues in berries beets flowers (Flavonones which give color to red grapes and berries are closely related to anthocyanins)
3-ring structures with varying numbers of OH groups in varying positions
Structure and therefore color is related to pH
predominantly red at low pH (acidic) blue at high pH (basic) and colorlesspale yellow at neutral pH
Temperature May break down at high temperatures and cause browning
Exposure to metal Form complexes with iron and aluminum and can change color
Color also affected when anthocyanins bond to sugars
Color Color of anthocyanins is pH dependent (they are
acidbase indicators)
Color Carotenes
Responsible for orange yellow and red colors in foods like carrots bananas tomatoes and saffron
Characterized by long hydrocarbon chains that often have carbon rings on the ends
Have nutritional value precursors to vitamin A (important in vision) act as antioxidants
Relatively stable during food processing but presence of C=C double bonds in hydrocarbon chain opens them up to oxidative degradation as seen in fats
Causes discoloration Prevents carotenoids from being able to be converted to
vitamin A
Color
β-carotene
Color Astaxanthin is a red pigment similar to
carotenoids found in lobster crab and salmon Bonds to proteins in the live animal and gives a
bluegreen color When heated bond to protein is broken which modifies
the structure and frequency of light absorbed appears bright red
Also an antioxidant
Color Chlorophyll
Green pigment responsible for plant photosynthesis Found in green vegetables Structure is centered around a porphyrin ring ndash a
planar ring system with 4 nitrogen atoms surrounding a central metal atom (magnesium in the case of chlorophyll)
Two forms chlorophyll A and chlorophyll B In chlorophyll B an aldehyde side chain replaces a
methyl side chain When cooked plant cells release acids
Causes an H+ ion to replace magnesium atom in center of structure causing a color change to an olivebrown
Opens the possibility for photodegradation (breakdown by light)
Color
chlorophyll A
(replaced with an aldehyde in chlorophyll B)
Color Heme
Pigment found in red blood cells Structure is similar to chlorophyll but there is an iron
atom in the center of the porphyrin ring Found in the protein myoglobin responsible for
oxygen transport Bright red when bound to oxygen but slow process
of autoxidation converts iron from +2 to +3 changing color to brown (less desirable) (myoglobin metmyoglobin)
Color change can be prevented by vacuum packing or packing with an inert gas like CO2
Color
heme groupin myoglobin
Color Color in foods is a result of the structures seen in
anthocyanins carotenoids chlorophylls and hemes All of these structures include an extensive network of
delocalized pi-bonds Alternating single and double bonds is called a conjugated
system The greater the extent of pi bond delocalization the closer
together in energy bonding and antibonding orbitals become All molecules absorb light energy as it promotes e-s between
molecular orbitals (bonding and antibonding orbitals) ndash energy required is proportional to distance between orbitals (less distance = less energy)
As orbitals are close together in a conjugated system low energy light (in the visible region) is absorbed for e- promotion
Color in these groups is the product of visible light absorption - color we see is complementary to the color(s) absorbed
Molecules without an extensive delocalized pi bond network (conjugated system) lack color as orbitals are further apart and only higher energy light promotes e-s (ex the anthocyanin carbinol)
Color Some pigments are water soluble because the
structures contain a large amount of -OH groups (H-bonding) Anthocyanins
Some pigments are fat soluble (ie not water soluble) because their structures contain little or no -OH groups (no H-bonding) carotenoids
Color
Many synthetic dyes are biochemically active and could be potentially harmful
Short-term toxicity easy to test and categorize but long-term effects are more difficult to study
Use of dyes in foods must be regulated but regulations are not standardized internationally posing issues in trade
Color Cooking foods often leads to browning
Two processes responsible Maillard reactions ndash combination of sugars and
proteins Caramelization ndash dehydration of sugar
Both involve removal of water molecule(s)
Color Maillard reactions
Sugars and proteins within the food combine in a condensation reaction
Aldehyde group in sugar (O atom) combines with amino group in protein (2 H atoms)
Initial condensation products polymerize to form brown-colored melanoidins
Maillard reactions only happen gt 140deg C Rate depends on amino acid present (ex lysine
reacts faster than cysteine)
initialcondensationproduct
Color Caramelization
Happens in foods high in carbohydrates Sugars dehydrate (lose H2O) at high temperatures
leaving behind C (dark brown color)
Browning intensifies the longer food is cooked eventually burning it (pure carbon is black)
Rate depends on Sugar type (fructose in fruits caramelizes very quickly) pH ndash extremes (high and low) promote caramelization
Genetically Modified Foods
Produced when organisms with modified DNA are used in food production Used to
Provide pest or disease resistance Bt corn contains toxin from bacillis thuringiensis that kills
insect pests Fungal-resistant potatoes Nematode-resistant bananas (nematode = worm)
Improve quality and range of crop Development of higher-yielding rice varieties Development of corn that can grow in dryer environments
Produce medicines or other products in large quantities Use of chickens that have been modified to lay eggs
containing human interferon (combats tumors and viruses) Use of cows to produce milk rich in omega-3 fatty acids
(polyunsaturated fats essential to growth development brain function)
Moth larva
Genetically Modified Foods
Drawbacks Are GM foods safe Will GM food production alter the natural ecosystem Do we understand enough about genetic
modification GM foods
Can cause allergic reactions in some people Have a slightly different composition from natural foods ndash
alters diet Produce altered pollen ndash might escape and cross with natural
species Long-term effects might be catastrophic unknown so far
Texture Food texture is related to physical properties
Hardness Elasticity Viscosity
These properties can be altered by Cooking Use of dispersed systems
Dispersed system = a stabilized macroscopically homogeneous mixture of two immiscible phases
(this means two substances that would not ordinarily mix ldquoappear tordquo on a macroscopic level (although at the molecular level they are still separate)
Texture Many types of dispersed systems name depends on
the physical states of the substances mixed LiquidSolid or SolidLiquid
Solid particles suspended in a liquid is called a suspension
Ex Blood (blood cells suspended in plasma) Liquid dispersed throughout a solid medium is called a
gel Ex Fruit Jelly (water trapped in a solid protein matrix)
LiquidLiquid Stable blend of two liquids that donrsquot mix is called an
emulsion Ex Mayonaisse (oil droplets suspended in aqueous system)
LiquidGas or GasLiquid Gas bubbles trapped in liquid medium is called a foam
Ex Whipped cream or egg whites Liquid droplets suspended in gas are called aerosols
Ex Aromas from food carried through the air
Texture Dispersed systems will slowly separate over
time Separation can be slowed by adding emulsifiers
Emulsifiers are stabilizers used to keep immiscible substance together
Have surfactant capability (can bind to both substances in suspension)
Similar to micelles in the action of soaps
Ex Lecithin Found commonly in egg
yolks One end is highly charged
and water soluble (bonds toaqueous phase) the otheris not (bonds to non-aqueous phase)
Texture Lecithin in mayonnaise
Lecithin is the emulsifier Mayonnaise made by beating eggs with
vinegar and oil Lecithin is found in eggs ndash charged
hydrophilic end bonds well to vinegar uncharged hydrophobic end bonds to oil
Vigorous beating produces many small oil droplets maximizing surface area for lecithin to act on and produce a stable emulsion
Stabilizers like sodium phosphate or metals are added to prevent separation (chefs use metal bowls)
hydrophilic
hydrophobic
Stereochemistry in Food Many food-specific compounds have a chiral
carbon atom and thus exist as two different enantiomers (optical isomers) Optical isomers are mirror images of one another ldquoOptical activityrdquo refers to the fact that the two mirror
image isomers rotate the direction of plane-polarized light in opposite directions
Enantiomers that rotate polarized light in a clockwise direction are said to be dextrorotatory (dex-tro-rota-tory) and have a + rotational value (d +) ndash In Latin dexter means ldquoright siderdquo
Enantiomers that rotate polarized light in an anti-clockwise direction are said to be laevorotatory (lay-vo-rota-tory) and have a ndash rotational value (l -) ndash In Latin laevus means ldquoleft siderdquo
There are two systems used to provide specific names to each enantiomeric form
Stereochemistry in Food Older system used for naming sugars and amino
acids Enantiomeric forms are labeled ldquoLrdquo and ldquoDrdquo
Again Laevus for left and Dexter for right Based off a compound called glyceraldehyde
chiral carbon
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Fats and Oils Unsaturated oils are more reactive due to the
possibility of addition reactions across the double bonds Are thus less stable and keep less well than saturated
fats Prone to auto-oxidation in the presence of light
(photo-oxidation) which is a reaction of the fats with atmospheric oxygen
Also more prone to hydrogenation (addition of hydrogen) hydrolysis (breaking of the fat back into glycerol and fatty acids) and microbial degradation
Fats and Oils Unsaturated fats are often artificially
hydrogenatedpartially hydrogenated Increases degree of saturation
Allows for control of texture because melting point is affected
Improves stability and shelf life as reactivity is decreased Improves cooking technique where more solid fats are
needed Hydrogen gas is added over a solid nickel catalyst
Double bonds converted to single bonds and degree of saturation increases
Drawback - decreases the health value as fats are healthier when mono- or poly-unsaturated
Ni(s)
Shelf Life Foods gradually become unfit for consumption
due to Spoilage (growth of organisms) Changes in texture smell flavor or appearance
Undesirable processes caused by Change in water content Chemical reactions Exposure to light Changes in temperature
Shelf life is the length of time a product can be stored without these undesirable changes occurring
Shelf Life Change in water content
Causes texture change Loss of water increases exposure to air and thus oxidation
Causes rancidity and discoloration Increase in water encourages microbial growth and
spoilage Chemical reactionstemperature change
Increased temperature increases rates of ldquoharmful reactionsrdquo
Changes in pH or temperature affect the amount of water in a food
Souring with decrease in pH Changes color Can decrease nutritional value
Light provides energy for ldquoharmfulrdquo chemical reactions
Shelf Life Rancidity is a common type of food
degradation Unpleasant textures smells and flavors of fats
and oils
Two types of rancidity Hydrolytic rancidity ndash ester bond in fat is broken
yielding free fatty acids (reverse of formation of a fat) Oxidative rancidity ndash oxygen reacts near the C=C
double bonds in unsaturated fats
Shelf Life Hydrolytic rancidity of fats and oils
reverse of fat formation uses water (hydro lysis = ldquowaterrdquo ldquosplittingrdquo) to split triglycerides back into glycerol and fatty acids
Encouraged by Lipase ndash an enzyme produced by microorganisms Deep frying ndash encourages reaction of fats with moisture in
food Releases free fatty acids
4 ndash 8 carbon fatty acids have a powerfully pungent aromaflavor
palmitic stearic oleic lauric acids give a soapy fatty feel to foods
Shelf Life Oxidative rancidity of fats and oils
Reaction of atmospheric oxygen with fats and oils initiates complex process producing highly reactive free radicals
Products include unpleasant smellingtasting byproducts
More of an issue with increasing degree of unsaturation (more C=C double bonds to react with)
Encouraged by the presence of light (photo-oxidation) Enzymes produced by microorganisms
Shelf Life Oxidative rancidity of fats and oils occurs in 3
steps Initiation by exposure to light ndash produces highly
reactive hydrocarbon radicals (species with an unpaired electron)
R-H R + H Propagation ndash radicals produce other radicals
R + O2 R-O-O ROO + R-H R-O-O-H + R
Termination ndash radicals encounter one another and end the reaction
R + R R-R R-O-O + R-O-O R-O-O-O-O-R R + R-O-O R-O-O-R
(R-H = unsaturated fat or oil R = hydrocarbon radical images on next slide)
Shelf Life Initiation
Shelf Life Propagation
Shelf Life Termination
Shelf Life Shelf life is prolonged by hindering spoilage
processes Packaging
Opaque or darkened packages block light Can be gas impermeable to limit exposure to oxygen and water Can be filled with inert gases or vacuum packed (no gases)
Storage Low temperatures slow harmful reactions Smoking or drying foods removes water and hinder microbial
growth Additives
Salt or sugar added to remove water and hinder microbial growth
KNO3 or NaNO3 salts are reducing agents and can prevent harmful oxidation reactions
Anti-microbial agents Pickling - Organic acids and their salts (ex benzoic acid and
benzoate salts) make pH unfavorable for microbial growth Fermentation ndash production of alcohol hinders microbial growth
Shelf Life Antioxidants delay oxidative degradation
processes by reacting with oxygen to contain free radical formation Can occur naturally
Vitamin C (ascorbic acid) ndash citrus and green vegetables Vitamin E (tocopherol) ndash nuts seeds grains canola oil Beta-carotene ndash carrots broccoli tomatoes peaches Selenium ndash shellfish meat eggs grains Foods high in natural antioxidants green tea blueberries
cranberries dark chocolate turmeric oregano Can be synthetic additives but may have harmful
side effects BHA BHT PG THBP TBHQ
these are all based around a phenol
groupwhich is not
necessarily found in natural
antioxidants
(Full structures in
data booklet)
Shelf Life Types of antioxidants
Free radical quenchers React with radicals to produce less reactive radicals (HA =
quencher)R-O-O + HA R-O-O-H + A
Chelating agents Form very stable complex ions with transition metals (which
can produce radicals) Found naturally in rosemary tea and mustard Salts of the organic acid EDTA are added as artificial chelating
agents Reducing agents
React with oxygen or hydroperoxides Vitamin C or carotenoids are natural reducing agents
Color Foods are colored by either pigments or dyes
Pigments occur naturally Dyes are added artificially and must be tested for
safety Dyes or pigments will absorb a range of light
frequencies and reflect others The color we see in a dye or pigment is the result of
the colors of light reflected not absorbed Ex chlorophyll in green leaf vegetables absorbs red
and blue light reflecting green Molecular structures all involve extensive
delocalized pi bonding (shown on next slide) This system of delocalized pi bonding (conjugated
system) is responsible for the color we see
Color Some of the most common natural pigment
groups are Anthocyanins
Ex Cyanidin Carotenoids
Ex Beta-carotene Chlorophyll
Ex Chlorophyll-A Heme
Ex Heme B group
heme B groupchlorophyll-A
cyanidin
β-carotene
Color Anthocyanins
Responsible for reds pinks blues in berries beets flowers (Flavonones which give color to red grapes and berries are closely related to anthocyanins)
3-ring structures with varying numbers of OH groups in varying positions
Structure and therefore color is related to pH
predominantly red at low pH (acidic) blue at high pH (basic) and colorlesspale yellow at neutral pH
Temperature May break down at high temperatures and cause browning
Exposure to metal Form complexes with iron and aluminum and can change color
Color also affected when anthocyanins bond to sugars
Color Color of anthocyanins is pH dependent (they are
acidbase indicators)
Color Carotenes
Responsible for orange yellow and red colors in foods like carrots bananas tomatoes and saffron
Characterized by long hydrocarbon chains that often have carbon rings on the ends
Have nutritional value precursors to vitamin A (important in vision) act as antioxidants
Relatively stable during food processing but presence of C=C double bonds in hydrocarbon chain opens them up to oxidative degradation as seen in fats
Causes discoloration Prevents carotenoids from being able to be converted to
vitamin A
Color
β-carotene
Color Astaxanthin is a red pigment similar to
carotenoids found in lobster crab and salmon Bonds to proteins in the live animal and gives a
bluegreen color When heated bond to protein is broken which modifies
the structure and frequency of light absorbed appears bright red
Also an antioxidant
Color Chlorophyll
Green pigment responsible for plant photosynthesis Found in green vegetables Structure is centered around a porphyrin ring ndash a
planar ring system with 4 nitrogen atoms surrounding a central metal atom (magnesium in the case of chlorophyll)
Two forms chlorophyll A and chlorophyll B In chlorophyll B an aldehyde side chain replaces a
methyl side chain When cooked plant cells release acids
Causes an H+ ion to replace magnesium atom in center of structure causing a color change to an olivebrown
Opens the possibility for photodegradation (breakdown by light)
Color
chlorophyll A
(replaced with an aldehyde in chlorophyll B)
Color Heme
Pigment found in red blood cells Structure is similar to chlorophyll but there is an iron
atom in the center of the porphyrin ring Found in the protein myoglobin responsible for
oxygen transport Bright red when bound to oxygen but slow process
of autoxidation converts iron from +2 to +3 changing color to brown (less desirable) (myoglobin metmyoglobin)
Color change can be prevented by vacuum packing or packing with an inert gas like CO2
Color
heme groupin myoglobin
Color Color in foods is a result of the structures seen in
anthocyanins carotenoids chlorophylls and hemes All of these structures include an extensive network of
delocalized pi-bonds Alternating single and double bonds is called a conjugated
system The greater the extent of pi bond delocalization the closer
together in energy bonding and antibonding orbitals become All molecules absorb light energy as it promotes e-s between
molecular orbitals (bonding and antibonding orbitals) ndash energy required is proportional to distance between orbitals (less distance = less energy)
As orbitals are close together in a conjugated system low energy light (in the visible region) is absorbed for e- promotion
Color in these groups is the product of visible light absorption - color we see is complementary to the color(s) absorbed
Molecules without an extensive delocalized pi bond network (conjugated system) lack color as orbitals are further apart and only higher energy light promotes e-s (ex the anthocyanin carbinol)
Color Some pigments are water soluble because the
structures contain a large amount of -OH groups (H-bonding) Anthocyanins
Some pigments are fat soluble (ie not water soluble) because their structures contain little or no -OH groups (no H-bonding) carotenoids
Color
Many synthetic dyes are biochemically active and could be potentially harmful
Short-term toxicity easy to test and categorize but long-term effects are more difficult to study
Use of dyes in foods must be regulated but regulations are not standardized internationally posing issues in trade
Color Cooking foods often leads to browning
Two processes responsible Maillard reactions ndash combination of sugars and
proteins Caramelization ndash dehydration of sugar
Both involve removal of water molecule(s)
Color Maillard reactions
Sugars and proteins within the food combine in a condensation reaction
Aldehyde group in sugar (O atom) combines with amino group in protein (2 H atoms)
Initial condensation products polymerize to form brown-colored melanoidins
Maillard reactions only happen gt 140deg C Rate depends on amino acid present (ex lysine
reacts faster than cysteine)
initialcondensationproduct
Color Caramelization
Happens in foods high in carbohydrates Sugars dehydrate (lose H2O) at high temperatures
leaving behind C (dark brown color)
Browning intensifies the longer food is cooked eventually burning it (pure carbon is black)
Rate depends on Sugar type (fructose in fruits caramelizes very quickly) pH ndash extremes (high and low) promote caramelization
Genetically Modified Foods
Produced when organisms with modified DNA are used in food production Used to
Provide pest or disease resistance Bt corn contains toxin from bacillis thuringiensis that kills
insect pests Fungal-resistant potatoes Nematode-resistant bananas (nematode = worm)
Improve quality and range of crop Development of higher-yielding rice varieties Development of corn that can grow in dryer environments
Produce medicines or other products in large quantities Use of chickens that have been modified to lay eggs
containing human interferon (combats tumors and viruses) Use of cows to produce milk rich in omega-3 fatty acids
(polyunsaturated fats essential to growth development brain function)
Moth larva
Genetically Modified Foods
Drawbacks Are GM foods safe Will GM food production alter the natural ecosystem Do we understand enough about genetic
modification GM foods
Can cause allergic reactions in some people Have a slightly different composition from natural foods ndash
alters diet Produce altered pollen ndash might escape and cross with natural
species Long-term effects might be catastrophic unknown so far
Texture Food texture is related to physical properties
Hardness Elasticity Viscosity
These properties can be altered by Cooking Use of dispersed systems
Dispersed system = a stabilized macroscopically homogeneous mixture of two immiscible phases
(this means two substances that would not ordinarily mix ldquoappear tordquo on a macroscopic level (although at the molecular level they are still separate)
Texture Many types of dispersed systems name depends on
the physical states of the substances mixed LiquidSolid or SolidLiquid
Solid particles suspended in a liquid is called a suspension
Ex Blood (blood cells suspended in plasma) Liquid dispersed throughout a solid medium is called a
gel Ex Fruit Jelly (water trapped in a solid protein matrix)
LiquidLiquid Stable blend of two liquids that donrsquot mix is called an
emulsion Ex Mayonaisse (oil droplets suspended in aqueous system)
LiquidGas or GasLiquid Gas bubbles trapped in liquid medium is called a foam
Ex Whipped cream or egg whites Liquid droplets suspended in gas are called aerosols
Ex Aromas from food carried through the air
Texture Dispersed systems will slowly separate over
time Separation can be slowed by adding emulsifiers
Emulsifiers are stabilizers used to keep immiscible substance together
Have surfactant capability (can bind to both substances in suspension)
Similar to micelles in the action of soaps
Ex Lecithin Found commonly in egg
yolks One end is highly charged
and water soluble (bonds toaqueous phase) the otheris not (bonds to non-aqueous phase)
Texture Lecithin in mayonnaise
Lecithin is the emulsifier Mayonnaise made by beating eggs with
vinegar and oil Lecithin is found in eggs ndash charged
hydrophilic end bonds well to vinegar uncharged hydrophobic end bonds to oil
Vigorous beating produces many small oil droplets maximizing surface area for lecithin to act on and produce a stable emulsion
Stabilizers like sodium phosphate or metals are added to prevent separation (chefs use metal bowls)
hydrophilic
hydrophobic
Stereochemistry in Food Many food-specific compounds have a chiral
carbon atom and thus exist as two different enantiomers (optical isomers) Optical isomers are mirror images of one another ldquoOptical activityrdquo refers to the fact that the two mirror
image isomers rotate the direction of plane-polarized light in opposite directions
Enantiomers that rotate polarized light in a clockwise direction are said to be dextrorotatory (dex-tro-rota-tory) and have a + rotational value (d +) ndash In Latin dexter means ldquoright siderdquo
Enantiomers that rotate polarized light in an anti-clockwise direction are said to be laevorotatory (lay-vo-rota-tory) and have a ndash rotational value (l -) ndash In Latin laevus means ldquoleft siderdquo
There are two systems used to provide specific names to each enantiomeric form
Stereochemistry in Food Older system used for naming sugars and amino
acids Enantiomeric forms are labeled ldquoLrdquo and ldquoDrdquo
Again Laevus for left and Dexter for right Based off a compound called glyceraldehyde
chiral carbon
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Fats and Oils Unsaturated fats are often artificially
hydrogenatedpartially hydrogenated Increases degree of saturation
Allows for control of texture because melting point is affected
Improves stability and shelf life as reactivity is decreased Improves cooking technique where more solid fats are
needed Hydrogen gas is added over a solid nickel catalyst
Double bonds converted to single bonds and degree of saturation increases
Drawback - decreases the health value as fats are healthier when mono- or poly-unsaturated
Ni(s)
Shelf Life Foods gradually become unfit for consumption
due to Spoilage (growth of organisms) Changes in texture smell flavor or appearance
Undesirable processes caused by Change in water content Chemical reactions Exposure to light Changes in temperature
Shelf life is the length of time a product can be stored without these undesirable changes occurring
Shelf Life Change in water content
Causes texture change Loss of water increases exposure to air and thus oxidation
Causes rancidity and discoloration Increase in water encourages microbial growth and
spoilage Chemical reactionstemperature change
Increased temperature increases rates of ldquoharmful reactionsrdquo
Changes in pH or temperature affect the amount of water in a food
Souring with decrease in pH Changes color Can decrease nutritional value
Light provides energy for ldquoharmfulrdquo chemical reactions
Shelf Life Rancidity is a common type of food
degradation Unpleasant textures smells and flavors of fats
and oils
Two types of rancidity Hydrolytic rancidity ndash ester bond in fat is broken
yielding free fatty acids (reverse of formation of a fat) Oxidative rancidity ndash oxygen reacts near the C=C
double bonds in unsaturated fats
Shelf Life Hydrolytic rancidity of fats and oils
reverse of fat formation uses water (hydro lysis = ldquowaterrdquo ldquosplittingrdquo) to split triglycerides back into glycerol and fatty acids
Encouraged by Lipase ndash an enzyme produced by microorganisms Deep frying ndash encourages reaction of fats with moisture in
food Releases free fatty acids
4 ndash 8 carbon fatty acids have a powerfully pungent aromaflavor
palmitic stearic oleic lauric acids give a soapy fatty feel to foods
Shelf Life Oxidative rancidity of fats and oils
Reaction of atmospheric oxygen with fats and oils initiates complex process producing highly reactive free radicals
Products include unpleasant smellingtasting byproducts
More of an issue with increasing degree of unsaturation (more C=C double bonds to react with)
Encouraged by the presence of light (photo-oxidation) Enzymes produced by microorganisms
Shelf Life Oxidative rancidity of fats and oils occurs in 3
steps Initiation by exposure to light ndash produces highly
reactive hydrocarbon radicals (species with an unpaired electron)
R-H R + H Propagation ndash radicals produce other radicals
R + O2 R-O-O ROO + R-H R-O-O-H + R
Termination ndash radicals encounter one another and end the reaction
R + R R-R R-O-O + R-O-O R-O-O-O-O-R R + R-O-O R-O-O-R
(R-H = unsaturated fat or oil R = hydrocarbon radical images on next slide)
Shelf Life Initiation
Shelf Life Propagation
Shelf Life Termination
Shelf Life Shelf life is prolonged by hindering spoilage
processes Packaging
Opaque or darkened packages block light Can be gas impermeable to limit exposure to oxygen and water Can be filled with inert gases or vacuum packed (no gases)
Storage Low temperatures slow harmful reactions Smoking or drying foods removes water and hinder microbial
growth Additives
Salt or sugar added to remove water and hinder microbial growth
KNO3 or NaNO3 salts are reducing agents and can prevent harmful oxidation reactions
Anti-microbial agents Pickling - Organic acids and their salts (ex benzoic acid and
benzoate salts) make pH unfavorable for microbial growth Fermentation ndash production of alcohol hinders microbial growth
Shelf Life Antioxidants delay oxidative degradation
processes by reacting with oxygen to contain free radical formation Can occur naturally
Vitamin C (ascorbic acid) ndash citrus and green vegetables Vitamin E (tocopherol) ndash nuts seeds grains canola oil Beta-carotene ndash carrots broccoli tomatoes peaches Selenium ndash shellfish meat eggs grains Foods high in natural antioxidants green tea blueberries
cranberries dark chocolate turmeric oregano Can be synthetic additives but may have harmful
side effects BHA BHT PG THBP TBHQ
these are all based around a phenol
groupwhich is not
necessarily found in natural
antioxidants
(Full structures in
data booklet)
Shelf Life Types of antioxidants
Free radical quenchers React with radicals to produce less reactive radicals (HA =
quencher)R-O-O + HA R-O-O-H + A
Chelating agents Form very stable complex ions with transition metals (which
can produce radicals) Found naturally in rosemary tea and mustard Salts of the organic acid EDTA are added as artificial chelating
agents Reducing agents
React with oxygen or hydroperoxides Vitamin C or carotenoids are natural reducing agents
Color Foods are colored by either pigments or dyes
Pigments occur naturally Dyes are added artificially and must be tested for
safety Dyes or pigments will absorb a range of light
frequencies and reflect others The color we see in a dye or pigment is the result of
the colors of light reflected not absorbed Ex chlorophyll in green leaf vegetables absorbs red
and blue light reflecting green Molecular structures all involve extensive
delocalized pi bonding (shown on next slide) This system of delocalized pi bonding (conjugated
system) is responsible for the color we see
Color Some of the most common natural pigment
groups are Anthocyanins
Ex Cyanidin Carotenoids
Ex Beta-carotene Chlorophyll
Ex Chlorophyll-A Heme
Ex Heme B group
heme B groupchlorophyll-A
cyanidin
β-carotene
Color Anthocyanins
Responsible for reds pinks blues in berries beets flowers (Flavonones which give color to red grapes and berries are closely related to anthocyanins)
3-ring structures with varying numbers of OH groups in varying positions
Structure and therefore color is related to pH
predominantly red at low pH (acidic) blue at high pH (basic) and colorlesspale yellow at neutral pH
Temperature May break down at high temperatures and cause browning
Exposure to metal Form complexes with iron and aluminum and can change color
Color also affected when anthocyanins bond to sugars
Color Color of anthocyanins is pH dependent (they are
acidbase indicators)
Color Carotenes
Responsible for orange yellow and red colors in foods like carrots bananas tomatoes and saffron
Characterized by long hydrocarbon chains that often have carbon rings on the ends
Have nutritional value precursors to vitamin A (important in vision) act as antioxidants
Relatively stable during food processing but presence of C=C double bonds in hydrocarbon chain opens them up to oxidative degradation as seen in fats
Causes discoloration Prevents carotenoids from being able to be converted to
vitamin A
Color
β-carotene
Color Astaxanthin is a red pigment similar to
carotenoids found in lobster crab and salmon Bonds to proteins in the live animal and gives a
bluegreen color When heated bond to protein is broken which modifies
the structure and frequency of light absorbed appears bright red
Also an antioxidant
Color Chlorophyll
Green pigment responsible for plant photosynthesis Found in green vegetables Structure is centered around a porphyrin ring ndash a
planar ring system with 4 nitrogen atoms surrounding a central metal atom (magnesium in the case of chlorophyll)
Two forms chlorophyll A and chlorophyll B In chlorophyll B an aldehyde side chain replaces a
methyl side chain When cooked plant cells release acids
Causes an H+ ion to replace magnesium atom in center of structure causing a color change to an olivebrown
Opens the possibility for photodegradation (breakdown by light)
Color
chlorophyll A
(replaced with an aldehyde in chlorophyll B)
Color Heme
Pigment found in red blood cells Structure is similar to chlorophyll but there is an iron
atom in the center of the porphyrin ring Found in the protein myoglobin responsible for
oxygen transport Bright red when bound to oxygen but slow process
of autoxidation converts iron from +2 to +3 changing color to brown (less desirable) (myoglobin metmyoglobin)
Color change can be prevented by vacuum packing or packing with an inert gas like CO2
Color
heme groupin myoglobin
Color Color in foods is a result of the structures seen in
anthocyanins carotenoids chlorophylls and hemes All of these structures include an extensive network of
delocalized pi-bonds Alternating single and double bonds is called a conjugated
system The greater the extent of pi bond delocalization the closer
together in energy bonding and antibonding orbitals become All molecules absorb light energy as it promotes e-s between
molecular orbitals (bonding and antibonding orbitals) ndash energy required is proportional to distance between orbitals (less distance = less energy)
As orbitals are close together in a conjugated system low energy light (in the visible region) is absorbed for e- promotion
Color in these groups is the product of visible light absorption - color we see is complementary to the color(s) absorbed
Molecules without an extensive delocalized pi bond network (conjugated system) lack color as orbitals are further apart and only higher energy light promotes e-s (ex the anthocyanin carbinol)
Color Some pigments are water soluble because the
structures contain a large amount of -OH groups (H-bonding) Anthocyanins
Some pigments are fat soluble (ie not water soluble) because their structures contain little or no -OH groups (no H-bonding) carotenoids
Color
Many synthetic dyes are biochemically active and could be potentially harmful
Short-term toxicity easy to test and categorize but long-term effects are more difficult to study
Use of dyes in foods must be regulated but regulations are not standardized internationally posing issues in trade
Color Cooking foods often leads to browning
Two processes responsible Maillard reactions ndash combination of sugars and
proteins Caramelization ndash dehydration of sugar
Both involve removal of water molecule(s)
Color Maillard reactions
Sugars and proteins within the food combine in a condensation reaction
Aldehyde group in sugar (O atom) combines with amino group in protein (2 H atoms)
Initial condensation products polymerize to form brown-colored melanoidins
Maillard reactions only happen gt 140deg C Rate depends on amino acid present (ex lysine
reacts faster than cysteine)
initialcondensationproduct
Color Caramelization
Happens in foods high in carbohydrates Sugars dehydrate (lose H2O) at high temperatures
leaving behind C (dark brown color)
Browning intensifies the longer food is cooked eventually burning it (pure carbon is black)
Rate depends on Sugar type (fructose in fruits caramelizes very quickly) pH ndash extremes (high and low) promote caramelization
Genetically Modified Foods
Produced when organisms with modified DNA are used in food production Used to
Provide pest or disease resistance Bt corn contains toxin from bacillis thuringiensis that kills
insect pests Fungal-resistant potatoes Nematode-resistant bananas (nematode = worm)
Improve quality and range of crop Development of higher-yielding rice varieties Development of corn that can grow in dryer environments
Produce medicines or other products in large quantities Use of chickens that have been modified to lay eggs
containing human interferon (combats tumors and viruses) Use of cows to produce milk rich in omega-3 fatty acids
(polyunsaturated fats essential to growth development brain function)
Moth larva
Genetically Modified Foods
Drawbacks Are GM foods safe Will GM food production alter the natural ecosystem Do we understand enough about genetic
modification GM foods
Can cause allergic reactions in some people Have a slightly different composition from natural foods ndash
alters diet Produce altered pollen ndash might escape and cross with natural
species Long-term effects might be catastrophic unknown so far
Texture Food texture is related to physical properties
Hardness Elasticity Viscosity
These properties can be altered by Cooking Use of dispersed systems
Dispersed system = a stabilized macroscopically homogeneous mixture of two immiscible phases
(this means two substances that would not ordinarily mix ldquoappear tordquo on a macroscopic level (although at the molecular level they are still separate)
Texture Many types of dispersed systems name depends on
the physical states of the substances mixed LiquidSolid or SolidLiquid
Solid particles suspended in a liquid is called a suspension
Ex Blood (blood cells suspended in plasma) Liquid dispersed throughout a solid medium is called a
gel Ex Fruit Jelly (water trapped in a solid protein matrix)
LiquidLiquid Stable blend of two liquids that donrsquot mix is called an
emulsion Ex Mayonaisse (oil droplets suspended in aqueous system)
LiquidGas or GasLiquid Gas bubbles trapped in liquid medium is called a foam
Ex Whipped cream or egg whites Liquid droplets suspended in gas are called aerosols
Ex Aromas from food carried through the air
Texture Dispersed systems will slowly separate over
time Separation can be slowed by adding emulsifiers
Emulsifiers are stabilizers used to keep immiscible substance together
Have surfactant capability (can bind to both substances in suspension)
Similar to micelles in the action of soaps
Ex Lecithin Found commonly in egg
yolks One end is highly charged
and water soluble (bonds toaqueous phase) the otheris not (bonds to non-aqueous phase)
Texture Lecithin in mayonnaise
Lecithin is the emulsifier Mayonnaise made by beating eggs with
vinegar and oil Lecithin is found in eggs ndash charged
hydrophilic end bonds well to vinegar uncharged hydrophobic end bonds to oil
Vigorous beating produces many small oil droplets maximizing surface area for lecithin to act on and produce a stable emulsion
Stabilizers like sodium phosphate or metals are added to prevent separation (chefs use metal bowls)
hydrophilic
hydrophobic
Stereochemistry in Food Many food-specific compounds have a chiral
carbon atom and thus exist as two different enantiomers (optical isomers) Optical isomers are mirror images of one another ldquoOptical activityrdquo refers to the fact that the two mirror
image isomers rotate the direction of plane-polarized light in opposite directions
Enantiomers that rotate polarized light in a clockwise direction are said to be dextrorotatory (dex-tro-rota-tory) and have a + rotational value (d +) ndash In Latin dexter means ldquoright siderdquo
Enantiomers that rotate polarized light in an anti-clockwise direction are said to be laevorotatory (lay-vo-rota-tory) and have a ndash rotational value (l -) ndash In Latin laevus means ldquoleft siderdquo
There are two systems used to provide specific names to each enantiomeric form
Stereochemistry in Food Older system used for naming sugars and amino
acids Enantiomeric forms are labeled ldquoLrdquo and ldquoDrdquo
Again Laevus for left and Dexter for right Based off a compound called glyceraldehyde
chiral carbon
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Shelf Life Foods gradually become unfit for consumption
due to Spoilage (growth of organisms) Changes in texture smell flavor or appearance
Undesirable processes caused by Change in water content Chemical reactions Exposure to light Changes in temperature
Shelf life is the length of time a product can be stored without these undesirable changes occurring
Shelf Life Change in water content
Causes texture change Loss of water increases exposure to air and thus oxidation
Causes rancidity and discoloration Increase in water encourages microbial growth and
spoilage Chemical reactionstemperature change
Increased temperature increases rates of ldquoharmful reactionsrdquo
Changes in pH or temperature affect the amount of water in a food
Souring with decrease in pH Changes color Can decrease nutritional value
Light provides energy for ldquoharmfulrdquo chemical reactions
Shelf Life Rancidity is a common type of food
degradation Unpleasant textures smells and flavors of fats
and oils
Two types of rancidity Hydrolytic rancidity ndash ester bond in fat is broken
yielding free fatty acids (reverse of formation of a fat) Oxidative rancidity ndash oxygen reacts near the C=C
double bonds in unsaturated fats
Shelf Life Hydrolytic rancidity of fats and oils
reverse of fat formation uses water (hydro lysis = ldquowaterrdquo ldquosplittingrdquo) to split triglycerides back into glycerol and fatty acids
Encouraged by Lipase ndash an enzyme produced by microorganisms Deep frying ndash encourages reaction of fats with moisture in
food Releases free fatty acids
4 ndash 8 carbon fatty acids have a powerfully pungent aromaflavor
palmitic stearic oleic lauric acids give a soapy fatty feel to foods
Shelf Life Oxidative rancidity of fats and oils
Reaction of atmospheric oxygen with fats and oils initiates complex process producing highly reactive free radicals
Products include unpleasant smellingtasting byproducts
More of an issue with increasing degree of unsaturation (more C=C double bonds to react with)
Encouraged by the presence of light (photo-oxidation) Enzymes produced by microorganisms
Shelf Life Oxidative rancidity of fats and oils occurs in 3
steps Initiation by exposure to light ndash produces highly
reactive hydrocarbon radicals (species with an unpaired electron)
R-H R + H Propagation ndash radicals produce other radicals
R + O2 R-O-O ROO + R-H R-O-O-H + R
Termination ndash radicals encounter one another and end the reaction
R + R R-R R-O-O + R-O-O R-O-O-O-O-R R + R-O-O R-O-O-R
(R-H = unsaturated fat or oil R = hydrocarbon radical images on next slide)
Shelf Life Initiation
Shelf Life Propagation
Shelf Life Termination
Shelf Life Shelf life is prolonged by hindering spoilage
processes Packaging
Opaque or darkened packages block light Can be gas impermeable to limit exposure to oxygen and water Can be filled with inert gases or vacuum packed (no gases)
Storage Low temperatures slow harmful reactions Smoking or drying foods removes water and hinder microbial
growth Additives
Salt or sugar added to remove water and hinder microbial growth
KNO3 or NaNO3 salts are reducing agents and can prevent harmful oxidation reactions
Anti-microbial agents Pickling - Organic acids and their salts (ex benzoic acid and
benzoate salts) make pH unfavorable for microbial growth Fermentation ndash production of alcohol hinders microbial growth
Shelf Life Antioxidants delay oxidative degradation
processes by reacting with oxygen to contain free radical formation Can occur naturally
Vitamin C (ascorbic acid) ndash citrus and green vegetables Vitamin E (tocopherol) ndash nuts seeds grains canola oil Beta-carotene ndash carrots broccoli tomatoes peaches Selenium ndash shellfish meat eggs grains Foods high in natural antioxidants green tea blueberries
cranberries dark chocolate turmeric oregano Can be synthetic additives but may have harmful
side effects BHA BHT PG THBP TBHQ
these are all based around a phenol
groupwhich is not
necessarily found in natural
antioxidants
(Full structures in
data booklet)
Shelf Life Types of antioxidants
Free radical quenchers React with radicals to produce less reactive radicals (HA =
quencher)R-O-O + HA R-O-O-H + A
Chelating agents Form very stable complex ions with transition metals (which
can produce radicals) Found naturally in rosemary tea and mustard Salts of the organic acid EDTA are added as artificial chelating
agents Reducing agents
React with oxygen or hydroperoxides Vitamin C or carotenoids are natural reducing agents
Color Foods are colored by either pigments or dyes
Pigments occur naturally Dyes are added artificially and must be tested for
safety Dyes or pigments will absorb a range of light
frequencies and reflect others The color we see in a dye or pigment is the result of
the colors of light reflected not absorbed Ex chlorophyll in green leaf vegetables absorbs red
and blue light reflecting green Molecular structures all involve extensive
delocalized pi bonding (shown on next slide) This system of delocalized pi bonding (conjugated
system) is responsible for the color we see
Color Some of the most common natural pigment
groups are Anthocyanins
Ex Cyanidin Carotenoids
Ex Beta-carotene Chlorophyll
Ex Chlorophyll-A Heme
Ex Heme B group
heme B groupchlorophyll-A
cyanidin
β-carotene
Color Anthocyanins
Responsible for reds pinks blues in berries beets flowers (Flavonones which give color to red grapes and berries are closely related to anthocyanins)
3-ring structures with varying numbers of OH groups in varying positions
Structure and therefore color is related to pH
predominantly red at low pH (acidic) blue at high pH (basic) and colorlesspale yellow at neutral pH
Temperature May break down at high temperatures and cause browning
Exposure to metal Form complexes with iron and aluminum and can change color
Color also affected when anthocyanins bond to sugars
Color Color of anthocyanins is pH dependent (they are
acidbase indicators)
Color Carotenes
Responsible for orange yellow and red colors in foods like carrots bananas tomatoes and saffron
Characterized by long hydrocarbon chains that often have carbon rings on the ends
Have nutritional value precursors to vitamin A (important in vision) act as antioxidants
Relatively stable during food processing but presence of C=C double bonds in hydrocarbon chain opens them up to oxidative degradation as seen in fats
Causes discoloration Prevents carotenoids from being able to be converted to
vitamin A
Color
β-carotene
Color Astaxanthin is a red pigment similar to
carotenoids found in lobster crab and salmon Bonds to proteins in the live animal and gives a
bluegreen color When heated bond to protein is broken which modifies
the structure and frequency of light absorbed appears bright red
Also an antioxidant
Color Chlorophyll
Green pigment responsible for plant photosynthesis Found in green vegetables Structure is centered around a porphyrin ring ndash a
planar ring system with 4 nitrogen atoms surrounding a central metal atom (magnesium in the case of chlorophyll)
Two forms chlorophyll A and chlorophyll B In chlorophyll B an aldehyde side chain replaces a
methyl side chain When cooked plant cells release acids
Causes an H+ ion to replace magnesium atom in center of structure causing a color change to an olivebrown
Opens the possibility for photodegradation (breakdown by light)
Color
chlorophyll A
(replaced with an aldehyde in chlorophyll B)
Color Heme
Pigment found in red blood cells Structure is similar to chlorophyll but there is an iron
atom in the center of the porphyrin ring Found in the protein myoglobin responsible for
oxygen transport Bright red when bound to oxygen but slow process
of autoxidation converts iron from +2 to +3 changing color to brown (less desirable) (myoglobin metmyoglobin)
Color change can be prevented by vacuum packing or packing with an inert gas like CO2
Color
heme groupin myoglobin
Color Color in foods is a result of the structures seen in
anthocyanins carotenoids chlorophylls and hemes All of these structures include an extensive network of
delocalized pi-bonds Alternating single and double bonds is called a conjugated
system The greater the extent of pi bond delocalization the closer
together in energy bonding and antibonding orbitals become All molecules absorb light energy as it promotes e-s between
molecular orbitals (bonding and antibonding orbitals) ndash energy required is proportional to distance between orbitals (less distance = less energy)
As orbitals are close together in a conjugated system low energy light (in the visible region) is absorbed for e- promotion
Color in these groups is the product of visible light absorption - color we see is complementary to the color(s) absorbed
Molecules without an extensive delocalized pi bond network (conjugated system) lack color as orbitals are further apart and only higher energy light promotes e-s (ex the anthocyanin carbinol)
Color Some pigments are water soluble because the
structures contain a large amount of -OH groups (H-bonding) Anthocyanins
Some pigments are fat soluble (ie not water soluble) because their structures contain little or no -OH groups (no H-bonding) carotenoids
Color
Many synthetic dyes are biochemically active and could be potentially harmful
Short-term toxicity easy to test and categorize but long-term effects are more difficult to study
Use of dyes in foods must be regulated but regulations are not standardized internationally posing issues in trade
Color Cooking foods often leads to browning
Two processes responsible Maillard reactions ndash combination of sugars and
proteins Caramelization ndash dehydration of sugar
Both involve removal of water molecule(s)
Color Maillard reactions
Sugars and proteins within the food combine in a condensation reaction
Aldehyde group in sugar (O atom) combines with amino group in protein (2 H atoms)
Initial condensation products polymerize to form brown-colored melanoidins
Maillard reactions only happen gt 140deg C Rate depends on amino acid present (ex lysine
reacts faster than cysteine)
initialcondensationproduct
Color Caramelization
Happens in foods high in carbohydrates Sugars dehydrate (lose H2O) at high temperatures
leaving behind C (dark brown color)
Browning intensifies the longer food is cooked eventually burning it (pure carbon is black)
Rate depends on Sugar type (fructose in fruits caramelizes very quickly) pH ndash extremes (high and low) promote caramelization
Genetically Modified Foods
Produced when organisms with modified DNA are used in food production Used to
Provide pest or disease resistance Bt corn contains toxin from bacillis thuringiensis that kills
insect pests Fungal-resistant potatoes Nematode-resistant bananas (nematode = worm)
Improve quality and range of crop Development of higher-yielding rice varieties Development of corn that can grow in dryer environments
Produce medicines or other products in large quantities Use of chickens that have been modified to lay eggs
containing human interferon (combats tumors and viruses) Use of cows to produce milk rich in omega-3 fatty acids
(polyunsaturated fats essential to growth development brain function)
Moth larva
Genetically Modified Foods
Drawbacks Are GM foods safe Will GM food production alter the natural ecosystem Do we understand enough about genetic
modification GM foods
Can cause allergic reactions in some people Have a slightly different composition from natural foods ndash
alters diet Produce altered pollen ndash might escape and cross with natural
species Long-term effects might be catastrophic unknown so far
Texture Food texture is related to physical properties
Hardness Elasticity Viscosity
These properties can be altered by Cooking Use of dispersed systems
Dispersed system = a stabilized macroscopically homogeneous mixture of two immiscible phases
(this means two substances that would not ordinarily mix ldquoappear tordquo on a macroscopic level (although at the molecular level they are still separate)
Texture Many types of dispersed systems name depends on
the physical states of the substances mixed LiquidSolid or SolidLiquid
Solid particles suspended in a liquid is called a suspension
Ex Blood (blood cells suspended in plasma) Liquid dispersed throughout a solid medium is called a
gel Ex Fruit Jelly (water trapped in a solid protein matrix)
LiquidLiquid Stable blend of two liquids that donrsquot mix is called an
emulsion Ex Mayonaisse (oil droplets suspended in aqueous system)
LiquidGas or GasLiquid Gas bubbles trapped in liquid medium is called a foam
Ex Whipped cream or egg whites Liquid droplets suspended in gas are called aerosols
Ex Aromas from food carried through the air
Texture Dispersed systems will slowly separate over
time Separation can be slowed by adding emulsifiers
Emulsifiers are stabilizers used to keep immiscible substance together
Have surfactant capability (can bind to both substances in suspension)
Similar to micelles in the action of soaps
Ex Lecithin Found commonly in egg
yolks One end is highly charged
and water soluble (bonds toaqueous phase) the otheris not (bonds to non-aqueous phase)
Texture Lecithin in mayonnaise
Lecithin is the emulsifier Mayonnaise made by beating eggs with
vinegar and oil Lecithin is found in eggs ndash charged
hydrophilic end bonds well to vinegar uncharged hydrophobic end bonds to oil
Vigorous beating produces many small oil droplets maximizing surface area for lecithin to act on and produce a stable emulsion
Stabilizers like sodium phosphate or metals are added to prevent separation (chefs use metal bowls)
hydrophilic
hydrophobic
Stereochemistry in Food Many food-specific compounds have a chiral
carbon atom and thus exist as two different enantiomers (optical isomers) Optical isomers are mirror images of one another ldquoOptical activityrdquo refers to the fact that the two mirror
image isomers rotate the direction of plane-polarized light in opposite directions
Enantiomers that rotate polarized light in a clockwise direction are said to be dextrorotatory (dex-tro-rota-tory) and have a + rotational value (d +) ndash In Latin dexter means ldquoright siderdquo
Enantiomers that rotate polarized light in an anti-clockwise direction are said to be laevorotatory (lay-vo-rota-tory) and have a ndash rotational value (l -) ndash In Latin laevus means ldquoleft siderdquo
There are two systems used to provide specific names to each enantiomeric form
Stereochemistry in Food Older system used for naming sugars and amino
acids Enantiomeric forms are labeled ldquoLrdquo and ldquoDrdquo
Again Laevus for left and Dexter for right Based off a compound called glyceraldehyde
chiral carbon
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Shelf Life Change in water content
Causes texture change Loss of water increases exposure to air and thus oxidation
Causes rancidity and discoloration Increase in water encourages microbial growth and
spoilage Chemical reactionstemperature change
Increased temperature increases rates of ldquoharmful reactionsrdquo
Changes in pH or temperature affect the amount of water in a food
Souring with decrease in pH Changes color Can decrease nutritional value
Light provides energy for ldquoharmfulrdquo chemical reactions
Shelf Life Rancidity is a common type of food
degradation Unpleasant textures smells and flavors of fats
and oils
Two types of rancidity Hydrolytic rancidity ndash ester bond in fat is broken
yielding free fatty acids (reverse of formation of a fat) Oxidative rancidity ndash oxygen reacts near the C=C
double bonds in unsaturated fats
Shelf Life Hydrolytic rancidity of fats and oils
reverse of fat formation uses water (hydro lysis = ldquowaterrdquo ldquosplittingrdquo) to split triglycerides back into glycerol and fatty acids
Encouraged by Lipase ndash an enzyme produced by microorganisms Deep frying ndash encourages reaction of fats with moisture in
food Releases free fatty acids
4 ndash 8 carbon fatty acids have a powerfully pungent aromaflavor
palmitic stearic oleic lauric acids give a soapy fatty feel to foods
Shelf Life Oxidative rancidity of fats and oils
Reaction of atmospheric oxygen with fats and oils initiates complex process producing highly reactive free radicals
Products include unpleasant smellingtasting byproducts
More of an issue with increasing degree of unsaturation (more C=C double bonds to react with)
Encouraged by the presence of light (photo-oxidation) Enzymes produced by microorganisms
Shelf Life Oxidative rancidity of fats and oils occurs in 3
steps Initiation by exposure to light ndash produces highly
reactive hydrocarbon radicals (species with an unpaired electron)
R-H R + H Propagation ndash radicals produce other radicals
R + O2 R-O-O ROO + R-H R-O-O-H + R
Termination ndash radicals encounter one another and end the reaction
R + R R-R R-O-O + R-O-O R-O-O-O-O-R R + R-O-O R-O-O-R
(R-H = unsaturated fat or oil R = hydrocarbon radical images on next slide)
Shelf Life Initiation
Shelf Life Propagation
Shelf Life Termination
Shelf Life Shelf life is prolonged by hindering spoilage
processes Packaging
Opaque or darkened packages block light Can be gas impermeable to limit exposure to oxygen and water Can be filled with inert gases or vacuum packed (no gases)
Storage Low temperatures slow harmful reactions Smoking or drying foods removes water and hinder microbial
growth Additives
Salt or sugar added to remove water and hinder microbial growth
KNO3 or NaNO3 salts are reducing agents and can prevent harmful oxidation reactions
Anti-microbial agents Pickling - Organic acids and their salts (ex benzoic acid and
benzoate salts) make pH unfavorable for microbial growth Fermentation ndash production of alcohol hinders microbial growth
Shelf Life Antioxidants delay oxidative degradation
processes by reacting with oxygen to contain free radical formation Can occur naturally
Vitamin C (ascorbic acid) ndash citrus and green vegetables Vitamin E (tocopherol) ndash nuts seeds grains canola oil Beta-carotene ndash carrots broccoli tomatoes peaches Selenium ndash shellfish meat eggs grains Foods high in natural antioxidants green tea blueberries
cranberries dark chocolate turmeric oregano Can be synthetic additives but may have harmful
side effects BHA BHT PG THBP TBHQ
these are all based around a phenol
groupwhich is not
necessarily found in natural
antioxidants
(Full structures in
data booklet)
Shelf Life Types of antioxidants
Free radical quenchers React with radicals to produce less reactive radicals (HA =
quencher)R-O-O + HA R-O-O-H + A
Chelating agents Form very stable complex ions with transition metals (which
can produce radicals) Found naturally in rosemary tea and mustard Salts of the organic acid EDTA are added as artificial chelating
agents Reducing agents
React with oxygen or hydroperoxides Vitamin C or carotenoids are natural reducing agents
Color Foods are colored by either pigments or dyes
Pigments occur naturally Dyes are added artificially and must be tested for
safety Dyes or pigments will absorb a range of light
frequencies and reflect others The color we see in a dye or pigment is the result of
the colors of light reflected not absorbed Ex chlorophyll in green leaf vegetables absorbs red
and blue light reflecting green Molecular structures all involve extensive
delocalized pi bonding (shown on next slide) This system of delocalized pi bonding (conjugated
system) is responsible for the color we see
Color Some of the most common natural pigment
groups are Anthocyanins
Ex Cyanidin Carotenoids
Ex Beta-carotene Chlorophyll
Ex Chlorophyll-A Heme
Ex Heme B group
heme B groupchlorophyll-A
cyanidin
β-carotene
Color Anthocyanins
Responsible for reds pinks blues in berries beets flowers (Flavonones which give color to red grapes and berries are closely related to anthocyanins)
3-ring structures with varying numbers of OH groups in varying positions
Structure and therefore color is related to pH
predominantly red at low pH (acidic) blue at high pH (basic) and colorlesspale yellow at neutral pH
Temperature May break down at high temperatures and cause browning
Exposure to metal Form complexes with iron and aluminum and can change color
Color also affected when anthocyanins bond to sugars
Color Color of anthocyanins is pH dependent (they are
acidbase indicators)
Color Carotenes
Responsible for orange yellow and red colors in foods like carrots bananas tomatoes and saffron
Characterized by long hydrocarbon chains that often have carbon rings on the ends
Have nutritional value precursors to vitamin A (important in vision) act as antioxidants
Relatively stable during food processing but presence of C=C double bonds in hydrocarbon chain opens them up to oxidative degradation as seen in fats
Causes discoloration Prevents carotenoids from being able to be converted to
vitamin A
Color
β-carotene
Color Astaxanthin is a red pigment similar to
carotenoids found in lobster crab and salmon Bonds to proteins in the live animal and gives a
bluegreen color When heated bond to protein is broken which modifies
the structure and frequency of light absorbed appears bright red
Also an antioxidant
Color Chlorophyll
Green pigment responsible for plant photosynthesis Found in green vegetables Structure is centered around a porphyrin ring ndash a
planar ring system with 4 nitrogen atoms surrounding a central metal atom (magnesium in the case of chlorophyll)
Two forms chlorophyll A and chlorophyll B In chlorophyll B an aldehyde side chain replaces a
methyl side chain When cooked plant cells release acids
Causes an H+ ion to replace magnesium atom in center of structure causing a color change to an olivebrown
Opens the possibility for photodegradation (breakdown by light)
Color
chlorophyll A
(replaced with an aldehyde in chlorophyll B)
Color Heme
Pigment found in red blood cells Structure is similar to chlorophyll but there is an iron
atom in the center of the porphyrin ring Found in the protein myoglobin responsible for
oxygen transport Bright red when bound to oxygen but slow process
of autoxidation converts iron from +2 to +3 changing color to brown (less desirable) (myoglobin metmyoglobin)
Color change can be prevented by vacuum packing or packing with an inert gas like CO2
Color
heme groupin myoglobin
Color Color in foods is a result of the structures seen in
anthocyanins carotenoids chlorophylls and hemes All of these structures include an extensive network of
delocalized pi-bonds Alternating single and double bonds is called a conjugated
system The greater the extent of pi bond delocalization the closer
together in energy bonding and antibonding orbitals become All molecules absorb light energy as it promotes e-s between
molecular orbitals (bonding and antibonding orbitals) ndash energy required is proportional to distance between orbitals (less distance = less energy)
As orbitals are close together in a conjugated system low energy light (in the visible region) is absorbed for e- promotion
Color in these groups is the product of visible light absorption - color we see is complementary to the color(s) absorbed
Molecules without an extensive delocalized pi bond network (conjugated system) lack color as orbitals are further apart and only higher energy light promotes e-s (ex the anthocyanin carbinol)
Color Some pigments are water soluble because the
structures contain a large amount of -OH groups (H-bonding) Anthocyanins
Some pigments are fat soluble (ie not water soluble) because their structures contain little or no -OH groups (no H-bonding) carotenoids
Color
Many synthetic dyes are biochemically active and could be potentially harmful
Short-term toxicity easy to test and categorize but long-term effects are more difficult to study
Use of dyes in foods must be regulated but regulations are not standardized internationally posing issues in trade
Color Cooking foods often leads to browning
Two processes responsible Maillard reactions ndash combination of sugars and
proteins Caramelization ndash dehydration of sugar
Both involve removal of water molecule(s)
Color Maillard reactions
Sugars and proteins within the food combine in a condensation reaction
Aldehyde group in sugar (O atom) combines with amino group in protein (2 H atoms)
Initial condensation products polymerize to form brown-colored melanoidins
Maillard reactions only happen gt 140deg C Rate depends on amino acid present (ex lysine
reacts faster than cysteine)
initialcondensationproduct
Color Caramelization
Happens in foods high in carbohydrates Sugars dehydrate (lose H2O) at high temperatures
leaving behind C (dark brown color)
Browning intensifies the longer food is cooked eventually burning it (pure carbon is black)
Rate depends on Sugar type (fructose in fruits caramelizes very quickly) pH ndash extremes (high and low) promote caramelization
Genetically Modified Foods
Produced when organisms with modified DNA are used in food production Used to
Provide pest or disease resistance Bt corn contains toxin from bacillis thuringiensis that kills
insect pests Fungal-resistant potatoes Nematode-resistant bananas (nematode = worm)
Improve quality and range of crop Development of higher-yielding rice varieties Development of corn that can grow in dryer environments
Produce medicines or other products in large quantities Use of chickens that have been modified to lay eggs
containing human interferon (combats tumors and viruses) Use of cows to produce milk rich in omega-3 fatty acids
(polyunsaturated fats essential to growth development brain function)
Moth larva
Genetically Modified Foods
Drawbacks Are GM foods safe Will GM food production alter the natural ecosystem Do we understand enough about genetic
modification GM foods
Can cause allergic reactions in some people Have a slightly different composition from natural foods ndash
alters diet Produce altered pollen ndash might escape and cross with natural
species Long-term effects might be catastrophic unknown so far
Texture Food texture is related to physical properties
Hardness Elasticity Viscosity
These properties can be altered by Cooking Use of dispersed systems
Dispersed system = a stabilized macroscopically homogeneous mixture of two immiscible phases
(this means two substances that would not ordinarily mix ldquoappear tordquo on a macroscopic level (although at the molecular level they are still separate)
Texture Many types of dispersed systems name depends on
the physical states of the substances mixed LiquidSolid or SolidLiquid
Solid particles suspended in a liquid is called a suspension
Ex Blood (blood cells suspended in plasma) Liquid dispersed throughout a solid medium is called a
gel Ex Fruit Jelly (water trapped in a solid protein matrix)
LiquidLiquid Stable blend of two liquids that donrsquot mix is called an
emulsion Ex Mayonaisse (oil droplets suspended in aqueous system)
LiquidGas or GasLiquid Gas bubbles trapped in liquid medium is called a foam
Ex Whipped cream or egg whites Liquid droplets suspended in gas are called aerosols
Ex Aromas from food carried through the air
Texture Dispersed systems will slowly separate over
time Separation can be slowed by adding emulsifiers
Emulsifiers are stabilizers used to keep immiscible substance together
Have surfactant capability (can bind to both substances in suspension)
Similar to micelles in the action of soaps
Ex Lecithin Found commonly in egg
yolks One end is highly charged
and water soluble (bonds toaqueous phase) the otheris not (bonds to non-aqueous phase)
Texture Lecithin in mayonnaise
Lecithin is the emulsifier Mayonnaise made by beating eggs with
vinegar and oil Lecithin is found in eggs ndash charged
hydrophilic end bonds well to vinegar uncharged hydrophobic end bonds to oil
Vigorous beating produces many small oil droplets maximizing surface area for lecithin to act on and produce a stable emulsion
Stabilizers like sodium phosphate or metals are added to prevent separation (chefs use metal bowls)
hydrophilic
hydrophobic
Stereochemistry in Food Many food-specific compounds have a chiral
carbon atom and thus exist as two different enantiomers (optical isomers) Optical isomers are mirror images of one another ldquoOptical activityrdquo refers to the fact that the two mirror
image isomers rotate the direction of plane-polarized light in opposite directions
Enantiomers that rotate polarized light in a clockwise direction are said to be dextrorotatory (dex-tro-rota-tory) and have a + rotational value (d +) ndash In Latin dexter means ldquoright siderdquo
Enantiomers that rotate polarized light in an anti-clockwise direction are said to be laevorotatory (lay-vo-rota-tory) and have a ndash rotational value (l -) ndash In Latin laevus means ldquoleft siderdquo
There are two systems used to provide specific names to each enantiomeric form
Stereochemistry in Food Older system used for naming sugars and amino
acids Enantiomeric forms are labeled ldquoLrdquo and ldquoDrdquo
Again Laevus for left and Dexter for right Based off a compound called glyceraldehyde
chiral carbon
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Shelf Life Rancidity is a common type of food
degradation Unpleasant textures smells and flavors of fats
and oils
Two types of rancidity Hydrolytic rancidity ndash ester bond in fat is broken
yielding free fatty acids (reverse of formation of a fat) Oxidative rancidity ndash oxygen reacts near the C=C
double bonds in unsaturated fats
Shelf Life Hydrolytic rancidity of fats and oils
reverse of fat formation uses water (hydro lysis = ldquowaterrdquo ldquosplittingrdquo) to split triglycerides back into glycerol and fatty acids
Encouraged by Lipase ndash an enzyme produced by microorganisms Deep frying ndash encourages reaction of fats with moisture in
food Releases free fatty acids
4 ndash 8 carbon fatty acids have a powerfully pungent aromaflavor
palmitic stearic oleic lauric acids give a soapy fatty feel to foods
Shelf Life Oxidative rancidity of fats and oils
Reaction of atmospheric oxygen with fats and oils initiates complex process producing highly reactive free radicals
Products include unpleasant smellingtasting byproducts
More of an issue with increasing degree of unsaturation (more C=C double bonds to react with)
Encouraged by the presence of light (photo-oxidation) Enzymes produced by microorganisms
Shelf Life Oxidative rancidity of fats and oils occurs in 3
steps Initiation by exposure to light ndash produces highly
reactive hydrocarbon radicals (species with an unpaired electron)
R-H R + H Propagation ndash radicals produce other radicals
R + O2 R-O-O ROO + R-H R-O-O-H + R
Termination ndash radicals encounter one another and end the reaction
R + R R-R R-O-O + R-O-O R-O-O-O-O-R R + R-O-O R-O-O-R
(R-H = unsaturated fat or oil R = hydrocarbon radical images on next slide)
Shelf Life Initiation
Shelf Life Propagation
Shelf Life Termination
Shelf Life Shelf life is prolonged by hindering spoilage
processes Packaging
Opaque or darkened packages block light Can be gas impermeable to limit exposure to oxygen and water Can be filled with inert gases or vacuum packed (no gases)
Storage Low temperatures slow harmful reactions Smoking or drying foods removes water and hinder microbial
growth Additives
Salt or sugar added to remove water and hinder microbial growth
KNO3 or NaNO3 salts are reducing agents and can prevent harmful oxidation reactions
Anti-microbial agents Pickling - Organic acids and their salts (ex benzoic acid and
benzoate salts) make pH unfavorable for microbial growth Fermentation ndash production of alcohol hinders microbial growth
Shelf Life Antioxidants delay oxidative degradation
processes by reacting with oxygen to contain free radical formation Can occur naturally
Vitamin C (ascorbic acid) ndash citrus and green vegetables Vitamin E (tocopherol) ndash nuts seeds grains canola oil Beta-carotene ndash carrots broccoli tomatoes peaches Selenium ndash shellfish meat eggs grains Foods high in natural antioxidants green tea blueberries
cranberries dark chocolate turmeric oregano Can be synthetic additives but may have harmful
side effects BHA BHT PG THBP TBHQ
these are all based around a phenol
groupwhich is not
necessarily found in natural
antioxidants
(Full structures in
data booklet)
Shelf Life Types of antioxidants
Free radical quenchers React with radicals to produce less reactive radicals (HA =
quencher)R-O-O + HA R-O-O-H + A
Chelating agents Form very stable complex ions with transition metals (which
can produce radicals) Found naturally in rosemary tea and mustard Salts of the organic acid EDTA are added as artificial chelating
agents Reducing agents
React with oxygen or hydroperoxides Vitamin C or carotenoids are natural reducing agents
Color Foods are colored by either pigments or dyes
Pigments occur naturally Dyes are added artificially and must be tested for
safety Dyes or pigments will absorb a range of light
frequencies and reflect others The color we see in a dye or pigment is the result of
the colors of light reflected not absorbed Ex chlorophyll in green leaf vegetables absorbs red
and blue light reflecting green Molecular structures all involve extensive
delocalized pi bonding (shown on next slide) This system of delocalized pi bonding (conjugated
system) is responsible for the color we see
Color Some of the most common natural pigment
groups are Anthocyanins
Ex Cyanidin Carotenoids
Ex Beta-carotene Chlorophyll
Ex Chlorophyll-A Heme
Ex Heme B group
heme B groupchlorophyll-A
cyanidin
β-carotene
Color Anthocyanins
Responsible for reds pinks blues in berries beets flowers (Flavonones which give color to red grapes and berries are closely related to anthocyanins)
3-ring structures with varying numbers of OH groups in varying positions
Structure and therefore color is related to pH
predominantly red at low pH (acidic) blue at high pH (basic) and colorlesspale yellow at neutral pH
Temperature May break down at high temperatures and cause browning
Exposure to metal Form complexes with iron and aluminum and can change color
Color also affected when anthocyanins bond to sugars
Color Color of anthocyanins is pH dependent (they are
acidbase indicators)
Color Carotenes
Responsible for orange yellow and red colors in foods like carrots bananas tomatoes and saffron
Characterized by long hydrocarbon chains that often have carbon rings on the ends
Have nutritional value precursors to vitamin A (important in vision) act as antioxidants
Relatively stable during food processing but presence of C=C double bonds in hydrocarbon chain opens them up to oxidative degradation as seen in fats
Causes discoloration Prevents carotenoids from being able to be converted to
vitamin A
Color
β-carotene
Color Astaxanthin is a red pigment similar to
carotenoids found in lobster crab and salmon Bonds to proteins in the live animal and gives a
bluegreen color When heated bond to protein is broken which modifies
the structure and frequency of light absorbed appears bright red
Also an antioxidant
Color Chlorophyll
Green pigment responsible for plant photosynthesis Found in green vegetables Structure is centered around a porphyrin ring ndash a
planar ring system with 4 nitrogen atoms surrounding a central metal atom (magnesium in the case of chlorophyll)
Two forms chlorophyll A and chlorophyll B In chlorophyll B an aldehyde side chain replaces a
methyl side chain When cooked plant cells release acids
Causes an H+ ion to replace magnesium atom in center of structure causing a color change to an olivebrown
Opens the possibility for photodegradation (breakdown by light)
Color
chlorophyll A
(replaced with an aldehyde in chlorophyll B)
Color Heme
Pigment found in red blood cells Structure is similar to chlorophyll but there is an iron
atom in the center of the porphyrin ring Found in the protein myoglobin responsible for
oxygen transport Bright red when bound to oxygen but slow process
of autoxidation converts iron from +2 to +3 changing color to brown (less desirable) (myoglobin metmyoglobin)
Color change can be prevented by vacuum packing or packing with an inert gas like CO2
Color
heme groupin myoglobin
Color Color in foods is a result of the structures seen in
anthocyanins carotenoids chlorophylls and hemes All of these structures include an extensive network of
delocalized pi-bonds Alternating single and double bonds is called a conjugated
system The greater the extent of pi bond delocalization the closer
together in energy bonding and antibonding orbitals become All molecules absorb light energy as it promotes e-s between
molecular orbitals (bonding and antibonding orbitals) ndash energy required is proportional to distance between orbitals (less distance = less energy)
As orbitals are close together in a conjugated system low energy light (in the visible region) is absorbed for e- promotion
Color in these groups is the product of visible light absorption - color we see is complementary to the color(s) absorbed
Molecules without an extensive delocalized pi bond network (conjugated system) lack color as orbitals are further apart and only higher energy light promotes e-s (ex the anthocyanin carbinol)
Color Some pigments are water soluble because the
structures contain a large amount of -OH groups (H-bonding) Anthocyanins
Some pigments are fat soluble (ie not water soluble) because their structures contain little or no -OH groups (no H-bonding) carotenoids
Color
Many synthetic dyes are biochemically active and could be potentially harmful
Short-term toxicity easy to test and categorize but long-term effects are more difficult to study
Use of dyes in foods must be regulated but regulations are not standardized internationally posing issues in trade
Color Cooking foods often leads to browning
Two processes responsible Maillard reactions ndash combination of sugars and
proteins Caramelization ndash dehydration of sugar
Both involve removal of water molecule(s)
Color Maillard reactions
Sugars and proteins within the food combine in a condensation reaction
Aldehyde group in sugar (O atom) combines with amino group in protein (2 H atoms)
Initial condensation products polymerize to form brown-colored melanoidins
Maillard reactions only happen gt 140deg C Rate depends on amino acid present (ex lysine
reacts faster than cysteine)
initialcondensationproduct
Color Caramelization
Happens in foods high in carbohydrates Sugars dehydrate (lose H2O) at high temperatures
leaving behind C (dark brown color)
Browning intensifies the longer food is cooked eventually burning it (pure carbon is black)
Rate depends on Sugar type (fructose in fruits caramelizes very quickly) pH ndash extremes (high and low) promote caramelization
Genetically Modified Foods
Produced when organisms with modified DNA are used in food production Used to
Provide pest or disease resistance Bt corn contains toxin from bacillis thuringiensis that kills
insect pests Fungal-resistant potatoes Nematode-resistant bananas (nematode = worm)
Improve quality and range of crop Development of higher-yielding rice varieties Development of corn that can grow in dryer environments
Produce medicines or other products in large quantities Use of chickens that have been modified to lay eggs
containing human interferon (combats tumors and viruses) Use of cows to produce milk rich in omega-3 fatty acids
(polyunsaturated fats essential to growth development brain function)
Moth larva
Genetically Modified Foods
Drawbacks Are GM foods safe Will GM food production alter the natural ecosystem Do we understand enough about genetic
modification GM foods
Can cause allergic reactions in some people Have a slightly different composition from natural foods ndash
alters diet Produce altered pollen ndash might escape and cross with natural
species Long-term effects might be catastrophic unknown so far
Texture Food texture is related to physical properties
Hardness Elasticity Viscosity
These properties can be altered by Cooking Use of dispersed systems
Dispersed system = a stabilized macroscopically homogeneous mixture of two immiscible phases
(this means two substances that would not ordinarily mix ldquoappear tordquo on a macroscopic level (although at the molecular level they are still separate)
Texture Many types of dispersed systems name depends on
the physical states of the substances mixed LiquidSolid or SolidLiquid
Solid particles suspended in a liquid is called a suspension
Ex Blood (blood cells suspended in plasma) Liquid dispersed throughout a solid medium is called a
gel Ex Fruit Jelly (water trapped in a solid protein matrix)
LiquidLiquid Stable blend of two liquids that donrsquot mix is called an
emulsion Ex Mayonaisse (oil droplets suspended in aqueous system)
LiquidGas or GasLiquid Gas bubbles trapped in liquid medium is called a foam
Ex Whipped cream or egg whites Liquid droplets suspended in gas are called aerosols
Ex Aromas from food carried through the air
Texture Dispersed systems will slowly separate over
time Separation can be slowed by adding emulsifiers
Emulsifiers are stabilizers used to keep immiscible substance together
Have surfactant capability (can bind to both substances in suspension)
Similar to micelles in the action of soaps
Ex Lecithin Found commonly in egg
yolks One end is highly charged
and water soluble (bonds toaqueous phase) the otheris not (bonds to non-aqueous phase)
Texture Lecithin in mayonnaise
Lecithin is the emulsifier Mayonnaise made by beating eggs with
vinegar and oil Lecithin is found in eggs ndash charged
hydrophilic end bonds well to vinegar uncharged hydrophobic end bonds to oil
Vigorous beating produces many small oil droplets maximizing surface area for lecithin to act on and produce a stable emulsion
Stabilizers like sodium phosphate or metals are added to prevent separation (chefs use metal bowls)
hydrophilic
hydrophobic
Stereochemistry in Food Many food-specific compounds have a chiral
carbon atom and thus exist as two different enantiomers (optical isomers) Optical isomers are mirror images of one another ldquoOptical activityrdquo refers to the fact that the two mirror
image isomers rotate the direction of plane-polarized light in opposite directions
Enantiomers that rotate polarized light in a clockwise direction are said to be dextrorotatory (dex-tro-rota-tory) and have a + rotational value (d +) ndash In Latin dexter means ldquoright siderdquo
Enantiomers that rotate polarized light in an anti-clockwise direction are said to be laevorotatory (lay-vo-rota-tory) and have a ndash rotational value (l -) ndash In Latin laevus means ldquoleft siderdquo
There are two systems used to provide specific names to each enantiomeric form
Stereochemistry in Food Older system used for naming sugars and amino
acids Enantiomeric forms are labeled ldquoLrdquo and ldquoDrdquo
Again Laevus for left and Dexter for right Based off a compound called glyceraldehyde
chiral carbon
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Shelf Life Hydrolytic rancidity of fats and oils
reverse of fat formation uses water (hydro lysis = ldquowaterrdquo ldquosplittingrdquo) to split triglycerides back into glycerol and fatty acids
Encouraged by Lipase ndash an enzyme produced by microorganisms Deep frying ndash encourages reaction of fats with moisture in
food Releases free fatty acids
4 ndash 8 carbon fatty acids have a powerfully pungent aromaflavor
palmitic stearic oleic lauric acids give a soapy fatty feel to foods
Shelf Life Oxidative rancidity of fats and oils
Reaction of atmospheric oxygen with fats and oils initiates complex process producing highly reactive free radicals
Products include unpleasant smellingtasting byproducts
More of an issue with increasing degree of unsaturation (more C=C double bonds to react with)
Encouraged by the presence of light (photo-oxidation) Enzymes produced by microorganisms
Shelf Life Oxidative rancidity of fats and oils occurs in 3
steps Initiation by exposure to light ndash produces highly
reactive hydrocarbon radicals (species with an unpaired electron)
R-H R + H Propagation ndash radicals produce other radicals
R + O2 R-O-O ROO + R-H R-O-O-H + R
Termination ndash radicals encounter one another and end the reaction
R + R R-R R-O-O + R-O-O R-O-O-O-O-R R + R-O-O R-O-O-R
(R-H = unsaturated fat or oil R = hydrocarbon radical images on next slide)
Shelf Life Initiation
Shelf Life Propagation
Shelf Life Termination
Shelf Life Shelf life is prolonged by hindering spoilage
processes Packaging
Opaque or darkened packages block light Can be gas impermeable to limit exposure to oxygen and water Can be filled with inert gases or vacuum packed (no gases)
Storage Low temperatures slow harmful reactions Smoking or drying foods removes water and hinder microbial
growth Additives
Salt or sugar added to remove water and hinder microbial growth
KNO3 or NaNO3 salts are reducing agents and can prevent harmful oxidation reactions
Anti-microbial agents Pickling - Organic acids and their salts (ex benzoic acid and
benzoate salts) make pH unfavorable for microbial growth Fermentation ndash production of alcohol hinders microbial growth
Shelf Life Antioxidants delay oxidative degradation
processes by reacting with oxygen to contain free radical formation Can occur naturally
Vitamin C (ascorbic acid) ndash citrus and green vegetables Vitamin E (tocopherol) ndash nuts seeds grains canola oil Beta-carotene ndash carrots broccoli tomatoes peaches Selenium ndash shellfish meat eggs grains Foods high in natural antioxidants green tea blueberries
cranberries dark chocolate turmeric oregano Can be synthetic additives but may have harmful
side effects BHA BHT PG THBP TBHQ
these are all based around a phenol
groupwhich is not
necessarily found in natural
antioxidants
(Full structures in
data booklet)
Shelf Life Types of antioxidants
Free radical quenchers React with radicals to produce less reactive radicals (HA =
quencher)R-O-O + HA R-O-O-H + A
Chelating agents Form very stable complex ions with transition metals (which
can produce radicals) Found naturally in rosemary tea and mustard Salts of the organic acid EDTA are added as artificial chelating
agents Reducing agents
React with oxygen or hydroperoxides Vitamin C or carotenoids are natural reducing agents
Color Foods are colored by either pigments or dyes
Pigments occur naturally Dyes are added artificially and must be tested for
safety Dyes or pigments will absorb a range of light
frequencies and reflect others The color we see in a dye or pigment is the result of
the colors of light reflected not absorbed Ex chlorophyll in green leaf vegetables absorbs red
and blue light reflecting green Molecular structures all involve extensive
delocalized pi bonding (shown on next slide) This system of delocalized pi bonding (conjugated
system) is responsible for the color we see
Color Some of the most common natural pigment
groups are Anthocyanins
Ex Cyanidin Carotenoids
Ex Beta-carotene Chlorophyll
Ex Chlorophyll-A Heme
Ex Heme B group
heme B groupchlorophyll-A
cyanidin
β-carotene
Color Anthocyanins
Responsible for reds pinks blues in berries beets flowers (Flavonones which give color to red grapes and berries are closely related to anthocyanins)
3-ring structures with varying numbers of OH groups in varying positions
Structure and therefore color is related to pH
predominantly red at low pH (acidic) blue at high pH (basic) and colorlesspale yellow at neutral pH
Temperature May break down at high temperatures and cause browning
Exposure to metal Form complexes with iron and aluminum and can change color
Color also affected when anthocyanins bond to sugars
Color Color of anthocyanins is pH dependent (they are
acidbase indicators)
Color Carotenes
Responsible for orange yellow and red colors in foods like carrots bananas tomatoes and saffron
Characterized by long hydrocarbon chains that often have carbon rings on the ends
Have nutritional value precursors to vitamin A (important in vision) act as antioxidants
Relatively stable during food processing but presence of C=C double bonds in hydrocarbon chain opens them up to oxidative degradation as seen in fats
Causes discoloration Prevents carotenoids from being able to be converted to
vitamin A
Color
β-carotene
Color Astaxanthin is a red pigment similar to
carotenoids found in lobster crab and salmon Bonds to proteins in the live animal and gives a
bluegreen color When heated bond to protein is broken which modifies
the structure and frequency of light absorbed appears bright red
Also an antioxidant
Color Chlorophyll
Green pigment responsible for plant photosynthesis Found in green vegetables Structure is centered around a porphyrin ring ndash a
planar ring system with 4 nitrogen atoms surrounding a central metal atom (magnesium in the case of chlorophyll)
Two forms chlorophyll A and chlorophyll B In chlorophyll B an aldehyde side chain replaces a
methyl side chain When cooked plant cells release acids
Causes an H+ ion to replace magnesium atom in center of structure causing a color change to an olivebrown
Opens the possibility for photodegradation (breakdown by light)
Color
chlorophyll A
(replaced with an aldehyde in chlorophyll B)
Color Heme
Pigment found in red blood cells Structure is similar to chlorophyll but there is an iron
atom in the center of the porphyrin ring Found in the protein myoglobin responsible for
oxygen transport Bright red when bound to oxygen but slow process
of autoxidation converts iron from +2 to +3 changing color to brown (less desirable) (myoglobin metmyoglobin)
Color change can be prevented by vacuum packing or packing with an inert gas like CO2
Color
heme groupin myoglobin
Color Color in foods is a result of the structures seen in
anthocyanins carotenoids chlorophylls and hemes All of these structures include an extensive network of
delocalized pi-bonds Alternating single and double bonds is called a conjugated
system The greater the extent of pi bond delocalization the closer
together in energy bonding and antibonding orbitals become All molecules absorb light energy as it promotes e-s between
molecular orbitals (bonding and antibonding orbitals) ndash energy required is proportional to distance between orbitals (less distance = less energy)
As orbitals are close together in a conjugated system low energy light (in the visible region) is absorbed for e- promotion
Color in these groups is the product of visible light absorption - color we see is complementary to the color(s) absorbed
Molecules without an extensive delocalized pi bond network (conjugated system) lack color as orbitals are further apart and only higher energy light promotes e-s (ex the anthocyanin carbinol)
Color Some pigments are water soluble because the
structures contain a large amount of -OH groups (H-bonding) Anthocyanins
Some pigments are fat soluble (ie not water soluble) because their structures contain little or no -OH groups (no H-bonding) carotenoids
Color
Many synthetic dyes are biochemically active and could be potentially harmful
Short-term toxicity easy to test and categorize but long-term effects are more difficult to study
Use of dyes in foods must be regulated but regulations are not standardized internationally posing issues in trade
Color Cooking foods often leads to browning
Two processes responsible Maillard reactions ndash combination of sugars and
proteins Caramelization ndash dehydration of sugar
Both involve removal of water molecule(s)
Color Maillard reactions
Sugars and proteins within the food combine in a condensation reaction
Aldehyde group in sugar (O atom) combines with amino group in protein (2 H atoms)
Initial condensation products polymerize to form brown-colored melanoidins
Maillard reactions only happen gt 140deg C Rate depends on amino acid present (ex lysine
reacts faster than cysteine)
initialcondensationproduct
Color Caramelization
Happens in foods high in carbohydrates Sugars dehydrate (lose H2O) at high temperatures
leaving behind C (dark brown color)
Browning intensifies the longer food is cooked eventually burning it (pure carbon is black)
Rate depends on Sugar type (fructose in fruits caramelizes very quickly) pH ndash extremes (high and low) promote caramelization
Genetically Modified Foods
Produced when organisms with modified DNA are used in food production Used to
Provide pest or disease resistance Bt corn contains toxin from bacillis thuringiensis that kills
insect pests Fungal-resistant potatoes Nematode-resistant bananas (nematode = worm)
Improve quality and range of crop Development of higher-yielding rice varieties Development of corn that can grow in dryer environments
Produce medicines or other products in large quantities Use of chickens that have been modified to lay eggs
containing human interferon (combats tumors and viruses) Use of cows to produce milk rich in omega-3 fatty acids
(polyunsaturated fats essential to growth development brain function)
Moth larva
Genetically Modified Foods
Drawbacks Are GM foods safe Will GM food production alter the natural ecosystem Do we understand enough about genetic
modification GM foods
Can cause allergic reactions in some people Have a slightly different composition from natural foods ndash
alters diet Produce altered pollen ndash might escape and cross with natural
species Long-term effects might be catastrophic unknown so far
Texture Food texture is related to physical properties
Hardness Elasticity Viscosity
These properties can be altered by Cooking Use of dispersed systems
Dispersed system = a stabilized macroscopically homogeneous mixture of two immiscible phases
(this means two substances that would not ordinarily mix ldquoappear tordquo on a macroscopic level (although at the molecular level they are still separate)
Texture Many types of dispersed systems name depends on
the physical states of the substances mixed LiquidSolid or SolidLiquid
Solid particles suspended in a liquid is called a suspension
Ex Blood (blood cells suspended in plasma) Liquid dispersed throughout a solid medium is called a
gel Ex Fruit Jelly (water trapped in a solid protein matrix)
LiquidLiquid Stable blend of two liquids that donrsquot mix is called an
emulsion Ex Mayonaisse (oil droplets suspended in aqueous system)
LiquidGas or GasLiquid Gas bubbles trapped in liquid medium is called a foam
Ex Whipped cream or egg whites Liquid droplets suspended in gas are called aerosols
Ex Aromas from food carried through the air
Texture Dispersed systems will slowly separate over
time Separation can be slowed by adding emulsifiers
Emulsifiers are stabilizers used to keep immiscible substance together
Have surfactant capability (can bind to both substances in suspension)
Similar to micelles in the action of soaps
Ex Lecithin Found commonly in egg
yolks One end is highly charged
and water soluble (bonds toaqueous phase) the otheris not (bonds to non-aqueous phase)
Texture Lecithin in mayonnaise
Lecithin is the emulsifier Mayonnaise made by beating eggs with
vinegar and oil Lecithin is found in eggs ndash charged
hydrophilic end bonds well to vinegar uncharged hydrophobic end bonds to oil
Vigorous beating produces many small oil droplets maximizing surface area for lecithin to act on and produce a stable emulsion
Stabilizers like sodium phosphate or metals are added to prevent separation (chefs use metal bowls)
hydrophilic
hydrophobic
Stereochemistry in Food Many food-specific compounds have a chiral
carbon atom and thus exist as two different enantiomers (optical isomers) Optical isomers are mirror images of one another ldquoOptical activityrdquo refers to the fact that the two mirror
image isomers rotate the direction of plane-polarized light in opposite directions
Enantiomers that rotate polarized light in a clockwise direction are said to be dextrorotatory (dex-tro-rota-tory) and have a + rotational value (d +) ndash In Latin dexter means ldquoright siderdquo
Enantiomers that rotate polarized light in an anti-clockwise direction are said to be laevorotatory (lay-vo-rota-tory) and have a ndash rotational value (l -) ndash In Latin laevus means ldquoleft siderdquo
There are two systems used to provide specific names to each enantiomeric form
Stereochemistry in Food Older system used for naming sugars and amino
acids Enantiomeric forms are labeled ldquoLrdquo and ldquoDrdquo
Again Laevus for left and Dexter for right Based off a compound called glyceraldehyde
chiral carbon
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Shelf Life Oxidative rancidity of fats and oils
Reaction of atmospheric oxygen with fats and oils initiates complex process producing highly reactive free radicals
Products include unpleasant smellingtasting byproducts
More of an issue with increasing degree of unsaturation (more C=C double bonds to react with)
Encouraged by the presence of light (photo-oxidation) Enzymes produced by microorganisms
Shelf Life Oxidative rancidity of fats and oils occurs in 3
steps Initiation by exposure to light ndash produces highly
reactive hydrocarbon radicals (species with an unpaired electron)
R-H R + H Propagation ndash radicals produce other radicals
R + O2 R-O-O ROO + R-H R-O-O-H + R
Termination ndash radicals encounter one another and end the reaction
R + R R-R R-O-O + R-O-O R-O-O-O-O-R R + R-O-O R-O-O-R
(R-H = unsaturated fat or oil R = hydrocarbon radical images on next slide)
Shelf Life Initiation
Shelf Life Propagation
Shelf Life Termination
Shelf Life Shelf life is prolonged by hindering spoilage
processes Packaging
Opaque or darkened packages block light Can be gas impermeable to limit exposure to oxygen and water Can be filled with inert gases or vacuum packed (no gases)
Storage Low temperatures slow harmful reactions Smoking or drying foods removes water and hinder microbial
growth Additives
Salt or sugar added to remove water and hinder microbial growth
KNO3 or NaNO3 salts are reducing agents and can prevent harmful oxidation reactions
Anti-microbial agents Pickling - Organic acids and their salts (ex benzoic acid and
benzoate salts) make pH unfavorable for microbial growth Fermentation ndash production of alcohol hinders microbial growth
Shelf Life Antioxidants delay oxidative degradation
processes by reacting with oxygen to contain free radical formation Can occur naturally
Vitamin C (ascorbic acid) ndash citrus and green vegetables Vitamin E (tocopherol) ndash nuts seeds grains canola oil Beta-carotene ndash carrots broccoli tomatoes peaches Selenium ndash shellfish meat eggs grains Foods high in natural antioxidants green tea blueberries
cranberries dark chocolate turmeric oregano Can be synthetic additives but may have harmful
side effects BHA BHT PG THBP TBHQ
these are all based around a phenol
groupwhich is not
necessarily found in natural
antioxidants
(Full structures in
data booklet)
Shelf Life Types of antioxidants
Free radical quenchers React with radicals to produce less reactive radicals (HA =
quencher)R-O-O + HA R-O-O-H + A
Chelating agents Form very stable complex ions with transition metals (which
can produce radicals) Found naturally in rosemary tea and mustard Salts of the organic acid EDTA are added as artificial chelating
agents Reducing agents
React with oxygen or hydroperoxides Vitamin C or carotenoids are natural reducing agents
Color Foods are colored by either pigments or dyes
Pigments occur naturally Dyes are added artificially and must be tested for
safety Dyes or pigments will absorb a range of light
frequencies and reflect others The color we see in a dye or pigment is the result of
the colors of light reflected not absorbed Ex chlorophyll in green leaf vegetables absorbs red
and blue light reflecting green Molecular structures all involve extensive
delocalized pi bonding (shown on next slide) This system of delocalized pi bonding (conjugated
system) is responsible for the color we see
Color Some of the most common natural pigment
groups are Anthocyanins
Ex Cyanidin Carotenoids
Ex Beta-carotene Chlorophyll
Ex Chlorophyll-A Heme
Ex Heme B group
heme B groupchlorophyll-A
cyanidin
β-carotene
Color Anthocyanins
Responsible for reds pinks blues in berries beets flowers (Flavonones which give color to red grapes and berries are closely related to anthocyanins)
3-ring structures with varying numbers of OH groups in varying positions
Structure and therefore color is related to pH
predominantly red at low pH (acidic) blue at high pH (basic) and colorlesspale yellow at neutral pH
Temperature May break down at high temperatures and cause browning
Exposure to metal Form complexes with iron and aluminum and can change color
Color also affected when anthocyanins bond to sugars
Color Color of anthocyanins is pH dependent (they are
acidbase indicators)
Color Carotenes
Responsible for orange yellow and red colors in foods like carrots bananas tomatoes and saffron
Characterized by long hydrocarbon chains that often have carbon rings on the ends
Have nutritional value precursors to vitamin A (important in vision) act as antioxidants
Relatively stable during food processing but presence of C=C double bonds in hydrocarbon chain opens them up to oxidative degradation as seen in fats
Causes discoloration Prevents carotenoids from being able to be converted to
vitamin A
Color
β-carotene
Color Astaxanthin is a red pigment similar to
carotenoids found in lobster crab and salmon Bonds to proteins in the live animal and gives a
bluegreen color When heated bond to protein is broken which modifies
the structure and frequency of light absorbed appears bright red
Also an antioxidant
Color Chlorophyll
Green pigment responsible for plant photosynthesis Found in green vegetables Structure is centered around a porphyrin ring ndash a
planar ring system with 4 nitrogen atoms surrounding a central metal atom (magnesium in the case of chlorophyll)
Two forms chlorophyll A and chlorophyll B In chlorophyll B an aldehyde side chain replaces a
methyl side chain When cooked plant cells release acids
Causes an H+ ion to replace magnesium atom in center of structure causing a color change to an olivebrown
Opens the possibility for photodegradation (breakdown by light)
Color
chlorophyll A
(replaced with an aldehyde in chlorophyll B)
Color Heme
Pigment found in red blood cells Structure is similar to chlorophyll but there is an iron
atom in the center of the porphyrin ring Found in the protein myoglobin responsible for
oxygen transport Bright red when bound to oxygen but slow process
of autoxidation converts iron from +2 to +3 changing color to brown (less desirable) (myoglobin metmyoglobin)
Color change can be prevented by vacuum packing or packing with an inert gas like CO2
Color
heme groupin myoglobin
Color Color in foods is a result of the structures seen in
anthocyanins carotenoids chlorophylls and hemes All of these structures include an extensive network of
delocalized pi-bonds Alternating single and double bonds is called a conjugated
system The greater the extent of pi bond delocalization the closer
together in energy bonding and antibonding orbitals become All molecules absorb light energy as it promotes e-s between
molecular orbitals (bonding and antibonding orbitals) ndash energy required is proportional to distance between orbitals (less distance = less energy)
As orbitals are close together in a conjugated system low energy light (in the visible region) is absorbed for e- promotion
Color in these groups is the product of visible light absorption - color we see is complementary to the color(s) absorbed
Molecules without an extensive delocalized pi bond network (conjugated system) lack color as orbitals are further apart and only higher energy light promotes e-s (ex the anthocyanin carbinol)
Color Some pigments are water soluble because the
structures contain a large amount of -OH groups (H-bonding) Anthocyanins
Some pigments are fat soluble (ie not water soluble) because their structures contain little or no -OH groups (no H-bonding) carotenoids
Color
Many synthetic dyes are biochemically active and could be potentially harmful
Short-term toxicity easy to test and categorize but long-term effects are more difficult to study
Use of dyes in foods must be regulated but regulations are not standardized internationally posing issues in trade
Color Cooking foods often leads to browning
Two processes responsible Maillard reactions ndash combination of sugars and
proteins Caramelization ndash dehydration of sugar
Both involve removal of water molecule(s)
Color Maillard reactions
Sugars and proteins within the food combine in a condensation reaction
Aldehyde group in sugar (O atom) combines with amino group in protein (2 H atoms)
Initial condensation products polymerize to form brown-colored melanoidins
Maillard reactions only happen gt 140deg C Rate depends on amino acid present (ex lysine
reacts faster than cysteine)
initialcondensationproduct
Color Caramelization
Happens in foods high in carbohydrates Sugars dehydrate (lose H2O) at high temperatures
leaving behind C (dark brown color)
Browning intensifies the longer food is cooked eventually burning it (pure carbon is black)
Rate depends on Sugar type (fructose in fruits caramelizes very quickly) pH ndash extremes (high and low) promote caramelization
Genetically Modified Foods
Produced when organisms with modified DNA are used in food production Used to
Provide pest or disease resistance Bt corn contains toxin from bacillis thuringiensis that kills
insect pests Fungal-resistant potatoes Nematode-resistant bananas (nematode = worm)
Improve quality and range of crop Development of higher-yielding rice varieties Development of corn that can grow in dryer environments
Produce medicines or other products in large quantities Use of chickens that have been modified to lay eggs
containing human interferon (combats tumors and viruses) Use of cows to produce milk rich in omega-3 fatty acids
(polyunsaturated fats essential to growth development brain function)
Moth larva
Genetically Modified Foods
Drawbacks Are GM foods safe Will GM food production alter the natural ecosystem Do we understand enough about genetic
modification GM foods
Can cause allergic reactions in some people Have a slightly different composition from natural foods ndash
alters diet Produce altered pollen ndash might escape and cross with natural
species Long-term effects might be catastrophic unknown so far
Texture Food texture is related to physical properties
Hardness Elasticity Viscosity
These properties can be altered by Cooking Use of dispersed systems
Dispersed system = a stabilized macroscopically homogeneous mixture of two immiscible phases
(this means two substances that would not ordinarily mix ldquoappear tordquo on a macroscopic level (although at the molecular level they are still separate)
Texture Many types of dispersed systems name depends on
the physical states of the substances mixed LiquidSolid or SolidLiquid
Solid particles suspended in a liquid is called a suspension
Ex Blood (blood cells suspended in plasma) Liquid dispersed throughout a solid medium is called a
gel Ex Fruit Jelly (water trapped in a solid protein matrix)
LiquidLiquid Stable blend of two liquids that donrsquot mix is called an
emulsion Ex Mayonaisse (oil droplets suspended in aqueous system)
LiquidGas or GasLiquid Gas bubbles trapped in liquid medium is called a foam
Ex Whipped cream or egg whites Liquid droplets suspended in gas are called aerosols
Ex Aromas from food carried through the air
Texture Dispersed systems will slowly separate over
time Separation can be slowed by adding emulsifiers
Emulsifiers are stabilizers used to keep immiscible substance together
Have surfactant capability (can bind to both substances in suspension)
Similar to micelles in the action of soaps
Ex Lecithin Found commonly in egg
yolks One end is highly charged
and water soluble (bonds toaqueous phase) the otheris not (bonds to non-aqueous phase)
Texture Lecithin in mayonnaise
Lecithin is the emulsifier Mayonnaise made by beating eggs with
vinegar and oil Lecithin is found in eggs ndash charged
hydrophilic end bonds well to vinegar uncharged hydrophobic end bonds to oil
Vigorous beating produces many small oil droplets maximizing surface area for lecithin to act on and produce a stable emulsion
Stabilizers like sodium phosphate or metals are added to prevent separation (chefs use metal bowls)
hydrophilic
hydrophobic
Stereochemistry in Food Many food-specific compounds have a chiral
carbon atom and thus exist as two different enantiomers (optical isomers) Optical isomers are mirror images of one another ldquoOptical activityrdquo refers to the fact that the two mirror
image isomers rotate the direction of plane-polarized light in opposite directions
Enantiomers that rotate polarized light in a clockwise direction are said to be dextrorotatory (dex-tro-rota-tory) and have a + rotational value (d +) ndash In Latin dexter means ldquoright siderdquo
Enantiomers that rotate polarized light in an anti-clockwise direction are said to be laevorotatory (lay-vo-rota-tory) and have a ndash rotational value (l -) ndash In Latin laevus means ldquoleft siderdquo
There are two systems used to provide specific names to each enantiomeric form
Stereochemistry in Food Older system used for naming sugars and amino
acids Enantiomeric forms are labeled ldquoLrdquo and ldquoDrdquo
Again Laevus for left and Dexter for right Based off a compound called glyceraldehyde
chiral carbon
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Shelf Life Oxidative rancidity of fats and oils occurs in 3
steps Initiation by exposure to light ndash produces highly
reactive hydrocarbon radicals (species with an unpaired electron)
R-H R + H Propagation ndash radicals produce other radicals
R + O2 R-O-O ROO + R-H R-O-O-H + R
Termination ndash radicals encounter one another and end the reaction
R + R R-R R-O-O + R-O-O R-O-O-O-O-R R + R-O-O R-O-O-R
(R-H = unsaturated fat or oil R = hydrocarbon radical images on next slide)
Shelf Life Initiation
Shelf Life Propagation
Shelf Life Termination
Shelf Life Shelf life is prolonged by hindering spoilage
processes Packaging
Opaque or darkened packages block light Can be gas impermeable to limit exposure to oxygen and water Can be filled with inert gases or vacuum packed (no gases)
Storage Low temperatures slow harmful reactions Smoking or drying foods removes water and hinder microbial
growth Additives
Salt or sugar added to remove water and hinder microbial growth
KNO3 or NaNO3 salts are reducing agents and can prevent harmful oxidation reactions
Anti-microbial agents Pickling - Organic acids and their salts (ex benzoic acid and
benzoate salts) make pH unfavorable for microbial growth Fermentation ndash production of alcohol hinders microbial growth
Shelf Life Antioxidants delay oxidative degradation
processes by reacting with oxygen to contain free radical formation Can occur naturally
Vitamin C (ascorbic acid) ndash citrus and green vegetables Vitamin E (tocopherol) ndash nuts seeds grains canola oil Beta-carotene ndash carrots broccoli tomatoes peaches Selenium ndash shellfish meat eggs grains Foods high in natural antioxidants green tea blueberries
cranberries dark chocolate turmeric oregano Can be synthetic additives but may have harmful
side effects BHA BHT PG THBP TBHQ
these are all based around a phenol
groupwhich is not
necessarily found in natural
antioxidants
(Full structures in
data booklet)
Shelf Life Types of antioxidants
Free radical quenchers React with radicals to produce less reactive radicals (HA =
quencher)R-O-O + HA R-O-O-H + A
Chelating agents Form very stable complex ions with transition metals (which
can produce radicals) Found naturally in rosemary tea and mustard Salts of the organic acid EDTA are added as artificial chelating
agents Reducing agents
React with oxygen or hydroperoxides Vitamin C or carotenoids are natural reducing agents
Color Foods are colored by either pigments or dyes
Pigments occur naturally Dyes are added artificially and must be tested for
safety Dyes or pigments will absorb a range of light
frequencies and reflect others The color we see in a dye or pigment is the result of
the colors of light reflected not absorbed Ex chlorophyll in green leaf vegetables absorbs red
and blue light reflecting green Molecular structures all involve extensive
delocalized pi bonding (shown on next slide) This system of delocalized pi bonding (conjugated
system) is responsible for the color we see
Color Some of the most common natural pigment
groups are Anthocyanins
Ex Cyanidin Carotenoids
Ex Beta-carotene Chlorophyll
Ex Chlorophyll-A Heme
Ex Heme B group
heme B groupchlorophyll-A
cyanidin
β-carotene
Color Anthocyanins
Responsible for reds pinks blues in berries beets flowers (Flavonones which give color to red grapes and berries are closely related to anthocyanins)
3-ring structures with varying numbers of OH groups in varying positions
Structure and therefore color is related to pH
predominantly red at low pH (acidic) blue at high pH (basic) and colorlesspale yellow at neutral pH
Temperature May break down at high temperatures and cause browning
Exposure to metal Form complexes with iron and aluminum and can change color
Color also affected when anthocyanins bond to sugars
Color Color of anthocyanins is pH dependent (they are
acidbase indicators)
Color Carotenes
Responsible for orange yellow and red colors in foods like carrots bananas tomatoes and saffron
Characterized by long hydrocarbon chains that often have carbon rings on the ends
Have nutritional value precursors to vitamin A (important in vision) act as antioxidants
Relatively stable during food processing but presence of C=C double bonds in hydrocarbon chain opens them up to oxidative degradation as seen in fats
Causes discoloration Prevents carotenoids from being able to be converted to
vitamin A
Color
β-carotene
Color Astaxanthin is a red pigment similar to
carotenoids found in lobster crab and salmon Bonds to proteins in the live animal and gives a
bluegreen color When heated bond to protein is broken which modifies
the structure and frequency of light absorbed appears bright red
Also an antioxidant
Color Chlorophyll
Green pigment responsible for plant photosynthesis Found in green vegetables Structure is centered around a porphyrin ring ndash a
planar ring system with 4 nitrogen atoms surrounding a central metal atom (magnesium in the case of chlorophyll)
Two forms chlorophyll A and chlorophyll B In chlorophyll B an aldehyde side chain replaces a
methyl side chain When cooked plant cells release acids
Causes an H+ ion to replace magnesium atom in center of structure causing a color change to an olivebrown
Opens the possibility for photodegradation (breakdown by light)
Color
chlorophyll A
(replaced with an aldehyde in chlorophyll B)
Color Heme
Pigment found in red blood cells Structure is similar to chlorophyll but there is an iron
atom in the center of the porphyrin ring Found in the protein myoglobin responsible for
oxygen transport Bright red when bound to oxygen but slow process
of autoxidation converts iron from +2 to +3 changing color to brown (less desirable) (myoglobin metmyoglobin)
Color change can be prevented by vacuum packing or packing with an inert gas like CO2
Color
heme groupin myoglobin
Color Color in foods is a result of the structures seen in
anthocyanins carotenoids chlorophylls and hemes All of these structures include an extensive network of
delocalized pi-bonds Alternating single and double bonds is called a conjugated
system The greater the extent of pi bond delocalization the closer
together in energy bonding and antibonding orbitals become All molecules absorb light energy as it promotes e-s between
molecular orbitals (bonding and antibonding orbitals) ndash energy required is proportional to distance between orbitals (less distance = less energy)
As orbitals are close together in a conjugated system low energy light (in the visible region) is absorbed for e- promotion
Color in these groups is the product of visible light absorption - color we see is complementary to the color(s) absorbed
Molecules without an extensive delocalized pi bond network (conjugated system) lack color as orbitals are further apart and only higher energy light promotes e-s (ex the anthocyanin carbinol)
Color Some pigments are water soluble because the
structures contain a large amount of -OH groups (H-bonding) Anthocyanins
Some pigments are fat soluble (ie not water soluble) because their structures contain little or no -OH groups (no H-bonding) carotenoids
Color
Many synthetic dyes are biochemically active and could be potentially harmful
Short-term toxicity easy to test and categorize but long-term effects are more difficult to study
Use of dyes in foods must be regulated but regulations are not standardized internationally posing issues in trade
Color Cooking foods often leads to browning
Two processes responsible Maillard reactions ndash combination of sugars and
proteins Caramelization ndash dehydration of sugar
Both involve removal of water molecule(s)
Color Maillard reactions
Sugars and proteins within the food combine in a condensation reaction
Aldehyde group in sugar (O atom) combines with amino group in protein (2 H atoms)
Initial condensation products polymerize to form brown-colored melanoidins
Maillard reactions only happen gt 140deg C Rate depends on amino acid present (ex lysine
reacts faster than cysteine)
initialcondensationproduct
Color Caramelization
Happens in foods high in carbohydrates Sugars dehydrate (lose H2O) at high temperatures
leaving behind C (dark brown color)
Browning intensifies the longer food is cooked eventually burning it (pure carbon is black)
Rate depends on Sugar type (fructose in fruits caramelizes very quickly) pH ndash extremes (high and low) promote caramelization
Genetically Modified Foods
Produced when organisms with modified DNA are used in food production Used to
Provide pest or disease resistance Bt corn contains toxin from bacillis thuringiensis that kills
insect pests Fungal-resistant potatoes Nematode-resistant bananas (nematode = worm)
Improve quality and range of crop Development of higher-yielding rice varieties Development of corn that can grow in dryer environments
Produce medicines or other products in large quantities Use of chickens that have been modified to lay eggs
containing human interferon (combats tumors and viruses) Use of cows to produce milk rich in omega-3 fatty acids
(polyunsaturated fats essential to growth development brain function)
Moth larva
Genetically Modified Foods
Drawbacks Are GM foods safe Will GM food production alter the natural ecosystem Do we understand enough about genetic
modification GM foods
Can cause allergic reactions in some people Have a slightly different composition from natural foods ndash
alters diet Produce altered pollen ndash might escape and cross with natural
species Long-term effects might be catastrophic unknown so far
Texture Food texture is related to physical properties
Hardness Elasticity Viscosity
These properties can be altered by Cooking Use of dispersed systems
Dispersed system = a stabilized macroscopically homogeneous mixture of two immiscible phases
(this means two substances that would not ordinarily mix ldquoappear tordquo on a macroscopic level (although at the molecular level they are still separate)
Texture Many types of dispersed systems name depends on
the physical states of the substances mixed LiquidSolid or SolidLiquid
Solid particles suspended in a liquid is called a suspension
Ex Blood (blood cells suspended in plasma) Liquid dispersed throughout a solid medium is called a
gel Ex Fruit Jelly (water trapped in a solid protein matrix)
LiquidLiquid Stable blend of two liquids that donrsquot mix is called an
emulsion Ex Mayonaisse (oil droplets suspended in aqueous system)
LiquidGas or GasLiquid Gas bubbles trapped in liquid medium is called a foam
Ex Whipped cream or egg whites Liquid droplets suspended in gas are called aerosols
Ex Aromas from food carried through the air
Texture Dispersed systems will slowly separate over
time Separation can be slowed by adding emulsifiers
Emulsifiers are stabilizers used to keep immiscible substance together
Have surfactant capability (can bind to both substances in suspension)
Similar to micelles in the action of soaps
Ex Lecithin Found commonly in egg
yolks One end is highly charged
and water soluble (bonds toaqueous phase) the otheris not (bonds to non-aqueous phase)
Texture Lecithin in mayonnaise
Lecithin is the emulsifier Mayonnaise made by beating eggs with
vinegar and oil Lecithin is found in eggs ndash charged
hydrophilic end bonds well to vinegar uncharged hydrophobic end bonds to oil
Vigorous beating produces many small oil droplets maximizing surface area for lecithin to act on and produce a stable emulsion
Stabilizers like sodium phosphate or metals are added to prevent separation (chefs use metal bowls)
hydrophilic
hydrophobic
Stereochemistry in Food Many food-specific compounds have a chiral
carbon atom and thus exist as two different enantiomers (optical isomers) Optical isomers are mirror images of one another ldquoOptical activityrdquo refers to the fact that the two mirror
image isomers rotate the direction of plane-polarized light in opposite directions
Enantiomers that rotate polarized light in a clockwise direction are said to be dextrorotatory (dex-tro-rota-tory) and have a + rotational value (d +) ndash In Latin dexter means ldquoright siderdquo
Enantiomers that rotate polarized light in an anti-clockwise direction are said to be laevorotatory (lay-vo-rota-tory) and have a ndash rotational value (l -) ndash In Latin laevus means ldquoleft siderdquo
There are two systems used to provide specific names to each enantiomeric form
Stereochemistry in Food Older system used for naming sugars and amino
acids Enantiomeric forms are labeled ldquoLrdquo and ldquoDrdquo
Again Laevus for left and Dexter for right Based off a compound called glyceraldehyde
chiral carbon
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Shelf Life Initiation
Shelf Life Propagation
Shelf Life Termination
Shelf Life Shelf life is prolonged by hindering spoilage
processes Packaging
Opaque or darkened packages block light Can be gas impermeable to limit exposure to oxygen and water Can be filled with inert gases or vacuum packed (no gases)
Storage Low temperatures slow harmful reactions Smoking or drying foods removes water and hinder microbial
growth Additives
Salt or sugar added to remove water and hinder microbial growth
KNO3 or NaNO3 salts are reducing agents and can prevent harmful oxidation reactions
Anti-microbial agents Pickling - Organic acids and their salts (ex benzoic acid and
benzoate salts) make pH unfavorable for microbial growth Fermentation ndash production of alcohol hinders microbial growth
Shelf Life Antioxidants delay oxidative degradation
processes by reacting with oxygen to contain free radical formation Can occur naturally
Vitamin C (ascorbic acid) ndash citrus and green vegetables Vitamin E (tocopherol) ndash nuts seeds grains canola oil Beta-carotene ndash carrots broccoli tomatoes peaches Selenium ndash shellfish meat eggs grains Foods high in natural antioxidants green tea blueberries
cranberries dark chocolate turmeric oregano Can be synthetic additives but may have harmful
side effects BHA BHT PG THBP TBHQ
these are all based around a phenol
groupwhich is not
necessarily found in natural
antioxidants
(Full structures in
data booklet)
Shelf Life Types of antioxidants
Free radical quenchers React with radicals to produce less reactive radicals (HA =
quencher)R-O-O + HA R-O-O-H + A
Chelating agents Form very stable complex ions with transition metals (which
can produce radicals) Found naturally in rosemary tea and mustard Salts of the organic acid EDTA are added as artificial chelating
agents Reducing agents
React with oxygen or hydroperoxides Vitamin C or carotenoids are natural reducing agents
Color Foods are colored by either pigments or dyes
Pigments occur naturally Dyes are added artificially and must be tested for
safety Dyes or pigments will absorb a range of light
frequencies and reflect others The color we see in a dye or pigment is the result of
the colors of light reflected not absorbed Ex chlorophyll in green leaf vegetables absorbs red
and blue light reflecting green Molecular structures all involve extensive
delocalized pi bonding (shown on next slide) This system of delocalized pi bonding (conjugated
system) is responsible for the color we see
Color Some of the most common natural pigment
groups are Anthocyanins
Ex Cyanidin Carotenoids
Ex Beta-carotene Chlorophyll
Ex Chlorophyll-A Heme
Ex Heme B group
heme B groupchlorophyll-A
cyanidin
β-carotene
Color Anthocyanins
Responsible for reds pinks blues in berries beets flowers (Flavonones which give color to red grapes and berries are closely related to anthocyanins)
3-ring structures with varying numbers of OH groups in varying positions
Structure and therefore color is related to pH
predominantly red at low pH (acidic) blue at high pH (basic) and colorlesspale yellow at neutral pH
Temperature May break down at high temperatures and cause browning
Exposure to metal Form complexes with iron and aluminum and can change color
Color also affected when anthocyanins bond to sugars
Color Color of anthocyanins is pH dependent (they are
acidbase indicators)
Color Carotenes
Responsible for orange yellow and red colors in foods like carrots bananas tomatoes and saffron
Characterized by long hydrocarbon chains that often have carbon rings on the ends
Have nutritional value precursors to vitamin A (important in vision) act as antioxidants
Relatively stable during food processing but presence of C=C double bonds in hydrocarbon chain opens them up to oxidative degradation as seen in fats
Causes discoloration Prevents carotenoids from being able to be converted to
vitamin A
Color
β-carotene
Color Astaxanthin is a red pigment similar to
carotenoids found in lobster crab and salmon Bonds to proteins in the live animal and gives a
bluegreen color When heated bond to protein is broken which modifies
the structure and frequency of light absorbed appears bright red
Also an antioxidant
Color Chlorophyll
Green pigment responsible for plant photosynthesis Found in green vegetables Structure is centered around a porphyrin ring ndash a
planar ring system with 4 nitrogen atoms surrounding a central metal atom (magnesium in the case of chlorophyll)
Two forms chlorophyll A and chlorophyll B In chlorophyll B an aldehyde side chain replaces a
methyl side chain When cooked plant cells release acids
Causes an H+ ion to replace magnesium atom in center of structure causing a color change to an olivebrown
Opens the possibility for photodegradation (breakdown by light)
Color
chlorophyll A
(replaced with an aldehyde in chlorophyll B)
Color Heme
Pigment found in red blood cells Structure is similar to chlorophyll but there is an iron
atom in the center of the porphyrin ring Found in the protein myoglobin responsible for
oxygen transport Bright red when bound to oxygen but slow process
of autoxidation converts iron from +2 to +3 changing color to brown (less desirable) (myoglobin metmyoglobin)
Color change can be prevented by vacuum packing or packing with an inert gas like CO2
Color
heme groupin myoglobin
Color Color in foods is a result of the structures seen in
anthocyanins carotenoids chlorophylls and hemes All of these structures include an extensive network of
delocalized pi-bonds Alternating single and double bonds is called a conjugated
system The greater the extent of pi bond delocalization the closer
together in energy bonding and antibonding orbitals become All molecules absorb light energy as it promotes e-s between
molecular orbitals (bonding and antibonding orbitals) ndash energy required is proportional to distance between orbitals (less distance = less energy)
As orbitals are close together in a conjugated system low energy light (in the visible region) is absorbed for e- promotion
Color in these groups is the product of visible light absorption - color we see is complementary to the color(s) absorbed
Molecules without an extensive delocalized pi bond network (conjugated system) lack color as orbitals are further apart and only higher energy light promotes e-s (ex the anthocyanin carbinol)
Color Some pigments are water soluble because the
structures contain a large amount of -OH groups (H-bonding) Anthocyanins
Some pigments are fat soluble (ie not water soluble) because their structures contain little or no -OH groups (no H-bonding) carotenoids
Color
Many synthetic dyes are biochemically active and could be potentially harmful
Short-term toxicity easy to test and categorize but long-term effects are more difficult to study
Use of dyes in foods must be regulated but regulations are not standardized internationally posing issues in trade
Color Cooking foods often leads to browning
Two processes responsible Maillard reactions ndash combination of sugars and
proteins Caramelization ndash dehydration of sugar
Both involve removal of water molecule(s)
Color Maillard reactions
Sugars and proteins within the food combine in a condensation reaction
Aldehyde group in sugar (O atom) combines with amino group in protein (2 H atoms)
Initial condensation products polymerize to form brown-colored melanoidins
Maillard reactions only happen gt 140deg C Rate depends on amino acid present (ex lysine
reacts faster than cysteine)
initialcondensationproduct
Color Caramelization
Happens in foods high in carbohydrates Sugars dehydrate (lose H2O) at high temperatures
leaving behind C (dark brown color)
Browning intensifies the longer food is cooked eventually burning it (pure carbon is black)
Rate depends on Sugar type (fructose in fruits caramelizes very quickly) pH ndash extremes (high and low) promote caramelization
Genetically Modified Foods
Produced when organisms with modified DNA are used in food production Used to
Provide pest or disease resistance Bt corn contains toxin from bacillis thuringiensis that kills
insect pests Fungal-resistant potatoes Nematode-resistant bananas (nematode = worm)
Improve quality and range of crop Development of higher-yielding rice varieties Development of corn that can grow in dryer environments
Produce medicines or other products in large quantities Use of chickens that have been modified to lay eggs
containing human interferon (combats tumors and viruses) Use of cows to produce milk rich in omega-3 fatty acids
(polyunsaturated fats essential to growth development brain function)
Moth larva
Genetically Modified Foods
Drawbacks Are GM foods safe Will GM food production alter the natural ecosystem Do we understand enough about genetic
modification GM foods
Can cause allergic reactions in some people Have a slightly different composition from natural foods ndash
alters diet Produce altered pollen ndash might escape and cross with natural
species Long-term effects might be catastrophic unknown so far
Texture Food texture is related to physical properties
Hardness Elasticity Viscosity
These properties can be altered by Cooking Use of dispersed systems
Dispersed system = a stabilized macroscopically homogeneous mixture of two immiscible phases
(this means two substances that would not ordinarily mix ldquoappear tordquo on a macroscopic level (although at the molecular level they are still separate)
Texture Many types of dispersed systems name depends on
the physical states of the substances mixed LiquidSolid or SolidLiquid
Solid particles suspended in a liquid is called a suspension
Ex Blood (blood cells suspended in plasma) Liquid dispersed throughout a solid medium is called a
gel Ex Fruit Jelly (water trapped in a solid protein matrix)
LiquidLiquid Stable blend of two liquids that donrsquot mix is called an
emulsion Ex Mayonaisse (oil droplets suspended in aqueous system)
LiquidGas or GasLiquid Gas bubbles trapped in liquid medium is called a foam
Ex Whipped cream or egg whites Liquid droplets suspended in gas are called aerosols
Ex Aromas from food carried through the air
Texture Dispersed systems will slowly separate over
time Separation can be slowed by adding emulsifiers
Emulsifiers are stabilizers used to keep immiscible substance together
Have surfactant capability (can bind to both substances in suspension)
Similar to micelles in the action of soaps
Ex Lecithin Found commonly in egg
yolks One end is highly charged
and water soluble (bonds toaqueous phase) the otheris not (bonds to non-aqueous phase)
Texture Lecithin in mayonnaise
Lecithin is the emulsifier Mayonnaise made by beating eggs with
vinegar and oil Lecithin is found in eggs ndash charged
hydrophilic end bonds well to vinegar uncharged hydrophobic end bonds to oil
Vigorous beating produces many small oil droplets maximizing surface area for lecithin to act on and produce a stable emulsion
Stabilizers like sodium phosphate or metals are added to prevent separation (chefs use metal bowls)
hydrophilic
hydrophobic
Stereochemistry in Food Many food-specific compounds have a chiral
carbon atom and thus exist as two different enantiomers (optical isomers) Optical isomers are mirror images of one another ldquoOptical activityrdquo refers to the fact that the two mirror
image isomers rotate the direction of plane-polarized light in opposite directions
Enantiomers that rotate polarized light in a clockwise direction are said to be dextrorotatory (dex-tro-rota-tory) and have a + rotational value (d +) ndash In Latin dexter means ldquoright siderdquo
Enantiomers that rotate polarized light in an anti-clockwise direction are said to be laevorotatory (lay-vo-rota-tory) and have a ndash rotational value (l -) ndash In Latin laevus means ldquoleft siderdquo
There are two systems used to provide specific names to each enantiomeric form
Stereochemistry in Food Older system used for naming sugars and amino
acids Enantiomeric forms are labeled ldquoLrdquo and ldquoDrdquo
Again Laevus for left and Dexter for right Based off a compound called glyceraldehyde
chiral carbon
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Shelf Life Propagation
Shelf Life Termination
Shelf Life Shelf life is prolonged by hindering spoilage
processes Packaging
Opaque or darkened packages block light Can be gas impermeable to limit exposure to oxygen and water Can be filled with inert gases or vacuum packed (no gases)
Storage Low temperatures slow harmful reactions Smoking or drying foods removes water and hinder microbial
growth Additives
Salt or sugar added to remove water and hinder microbial growth
KNO3 or NaNO3 salts are reducing agents and can prevent harmful oxidation reactions
Anti-microbial agents Pickling - Organic acids and their salts (ex benzoic acid and
benzoate salts) make pH unfavorable for microbial growth Fermentation ndash production of alcohol hinders microbial growth
Shelf Life Antioxidants delay oxidative degradation
processes by reacting with oxygen to contain free radical formation Can occur naturally
Vitamin C (ascorbic acid) ndash citrus and green vegetables Vitamin E (tocopherol) ndash nuts seeds grains canola oil Beta-carotene ndash carrots broccoli tomatoes peaches Selenium ndash shellfish meat eggs grains Foods high in natural antioxidants green tea blueberries
cranberries dark chocolate turmeric oregano Can be synthetic additives but may have harmful
side effects BHA BHT PG THBP TBHQ
these are all based around a phenol
groupwhich is not
necessarily found in natural
antioxidants
(Full structures in
data booklet)
Shelf Life Types of antioxidants
Free radical quenchers React with radicals to produce less reactive radicals (HA =
quencher)R-O-O + HA R-O-O-H + A
Chelating agents Form very stable complex ions with transition metals (which
can produce radicals) Found naturally in rosemary tea and mustard Salts of the organic acid EDTA are added as artificial chelating
agents Reducing agents
React with oxygen or hydroperoxides Vitamin C or carotenoids are natural reducing agents
Color Foods are colored by either pigments or dyes
Pigments occur naturally Dyes are added artificially and must be tested for
safety Dyes or pigments will absorb a range of light
frequencies and reflect others The color we see in a dye or pigment is the result of
the colors of light reflected not absorbed Ex chlorophyll in green leaf vegetables absorbs red
and blue light reflecting green Molecular structures all involve extensive
delocalized pi bonding (shown on next slide) This system of delocalized pi bonding (conjugated
system) is responsible for the color we see
Color Some of the most common natural pigment
groups are Anthocyanins
Ex Cyanidin Carotenoids
Ex Beta-carotene Chlorophyll
Ex Chlorophyll-A Heme
Ex Heme B group
heme B groupchlorophyll-A
cyanidin
β-carotene
Color Anthocyanins
Responsible for reds pinks blues in berries beets flowers (Flavonones which give color to red grapes and berries are closely related to anthocyanins)
3-ring structures with varying numbers of OH groups in varying positions
Structure and therefore color is related to pH
predominantly red at low pH (acidic) blue at high pH (basic) and colorlesspale yellow at neutral pH
Temperature May break down at high temperatures and cause browning
Exposure to metal Form complexes with iron and aluminum and can change color
Color also affected when anthocyanins bond to sugars
Color Color of anthocyanins is pH dependent (they are
acidbase indicators)
Color Carotenes
Responsible for orange yellow and red colors in foods like carrots bananas tomatoes and saffron
Characterized by long hydrocarbon chains that often have carbon rings on the ends
Have nutritional value precursors to vitamin A (important in vision) act as antioxidants
Relatively stable during food processing but presence of C=C double bonds in hydrocarbon chain opens them up to oxidative degradation as seen in fats
Causes discoloration Prevents carotenoids from being able to be converted to
vitamin A
Color
β-carotene
Color Astaxanthin is a red pigment similar to
carotenoids found in lobster crab and salmon Bonds to proteins in the live animal and gives a
bluegreen color When heated bond to protein is broken which modifies
the structure and frequency of light absorbed appears bright red
Also an antioxidant
Color Chlorophyll
Green pigment responsible for plant photosynthesis Found in green vegetables Structure is centered around a porphyrin ring ndash a
planar ring system with 4 nitrogen atoms surrounding a central metal atom (magnesium in the case of chlorophyll)
Two forms chlorophyll A and chlorophyll B In chlorophyll B an aldehyde side chain replaces a
methyl side chain When cooked plant cells release acids
Causes an H+ ion to replace magnesium atom in center of structure causing a color change to an olivebrown
Opens the possibility for photodegradation (breakdown by light)
Color
chlorophyll A
(replaced with an aldehyde in chlorophyll B)
Color Heme
Pigment found in red blood cells Structure is similar to chlorophyll but there is an iron
atom in the center of the porphyrin ring Found in the protein myoglobin responsible for
oxygen transport Bright red when bound to oxygen but slow process
of autoxidation converts iron from +2 to +3 changing color to brown (less desirable) (myoglobin metmyoglobin)
Color change can be prevented by vacuum packing or packing with an inert gas like CO2
Color
heme groupin myoglobin
Color Color in foods is a result of the structures seen in
anthocyanins carotenoids chlorophylls and hemes All of these structures include an extensive network of
delocalized pi-bonds Alternating single and double bonds is called a conjugated
system The greater the extent of pi bond delocalization the closer
together in energy bonding and antibonding orbitals become All molecules absorb light energy as it promotes e-s between
molecular orbitals (bonding and antibonding orbitals) ndash energy required is proportional to distance between orbitals (less distance = less energy)
As orbitals are close together in a conjugated system low energy light (in the visible region) is absorbed for e- promotion
Color in these groups is the product of visible light absorption - color we see is complementary to the color(s) absorbed
Molecules without an extensive delocalized pi bond network (conjugated system) lack color as orbitals are further apart and only higher energy light promotes e-s (ex the anthocyanin carbinol)
Color Some pigments are water soluble because the
structures contain a large amount of -OH groups (H-bonding) Anthocyanins
Some pigments are fat soluble (ie not water soluble) because their structures contain little or no -OH groups (no H-bonding) carotenoids
Color
Many synthetic dyes are biochemically active and could be potentially harmful
Short-term toxicity easy to test and categorize but long-term effects are more difficult to study
Use of dyes in foods must be regulated but regulations are not standardized internationally posing issues in trade
Color Cooking foods often leads to browning
Two processes responsible Maillard reactions ndash combination of sugars and
proteins Caramelization ndash dehydration of sugar
Both involve removal of water molecule(s)
Color Maillard reactions
Sugars and proteins within the food combine in a condensation reaction
Aldehyde group in sugar (O atom) combines with amino group in protein (2 H atoms)
Initial condensation products polymerize to form brown-colored melanoidins
Maillard reactions only happen gt 140deg C Rate depends on amino acid present (ex lysine
reacts faster than cysteine)
initialcondensationproduct
Color Caramelization
Happens in foods high in carbohydrates Sugars dehydrate (lose H2O) at high temperatures
leaving behind C (dark brown color)
Browning intensifies the longer food is cooked eventually burning it (pure carbon is black)
Rate depends on Sugar type (fructose in fruits caramelizes very quickly) pH ndash extremes (high and low) promote caramelization
Genetically Modified Foods
Produced when organisms with modified DNA are used in food production Used to
Provide pest or disease resistance Bt corn contains toxin from bacillis thuringiensis that kills
insect pests Fungal-resistant potatoes Nematode-resistant bananas (nematode = worm)
Improve quality and range of crop Development of higher-yielding rice varieties Development of corn that can grow in dryer environments
Produce medicines or other products in large quantities Use of chickens that have been modified to lay eggs
containing human interferon (combats tumors and viruses) Use of cows to produce milk rich in omega-3 fatty acids
(polyunsaturated fats essential to growth development brain function)
Moth larva
Genetically Modified Foods
Drawbacks Are GM foods safe Will GM food production alter the natural ecosystem Do we understand enough about genetic
modification GM foods
Can cause allergic reactions in some people Have a slightly different composition from natural foods ndash
alters diet Produce altered pollen ndash might escape and cross with natural
species Long-term effects might be catastrophic unknown so far
Texture Food texture is related to physical properties
Hardness Elasticity Viscosity
These properties can be altered by Cooking Use of dispersed systems
Dispersed system = a stabilized macroscopically homogeneous mixture of two immiscible phases
(this means two substances that would not ordinarily mix ldquoappear tordquo on a macroscopic level (although at the molecular level they are still separate)
Texture Many types of dispersed systems name depends on
the physical states of the substances mixed LiquidSolid or SolidLiquid
Solid particles suspended in a liquid is called a suspension
Ex Blood (blood cells suspended in plasma) Liquid dispersed throughout a solid medium is called a
gel Ex Fruit Jelly (water trapped in a solid protein matrix)
LiquidLiquid Stable blend of two liquids that donrsquot mix is called an
emulsion Ex Mayonaisse (oil droplets suspended in aqueous system)
LiquidGas or GasLiquid Gas bubbles trapped in liquid medium is called a foam
Ex Whipped cream or egg whites Liquid droplets suspended in gas are called aerosols
Ex Aromas from food carried through the air
Texture Dispersed systems will slowly separate over
time Separation can be slowed by adding emulsifiers
Emulsifiers are stabilizers used to keep immiscible substance together
Have surfactant capability (can bind to both substances in suspension)
Similar to micelles in the action of soaps
Ex Lecithin Found commonly in egg
yolks One end is highly charged
and water soluble (bonds toaqueous phase) the otheris not (bonds to non-aqueous phase)
Texture Lecithin in mayonnaise
Lecithin is the emulsifier Mayonnaise made by beating eggs with
vinegar and oil Lecithin is found in eggs ndash charged
hydrophilic end bonds well to vinegar uncharged hydrophobic end bonds to oil
Vigorous beating produces many small oil droplets maximizing surface area for lecithin to act on and produce a stable emulsion
Stabilizers like sodium phosphate or metals are added to prevent separation (chefs use metal bowls)
hydrophilic
hydrophobic
Stereochemistry in Food Many food-specific compounds have a chiral
carbon atom and thus exist as two different enantiomers (optical isomers) Optical isomers are mirror images of one another ldquoOptical activityrdquo refers to the fact that the two mirror
image isomers rotate the direction of plane-polarized light in opposite directions
Enantiomers that rotate polarized light in a clockwise direction are said to be dextrorotatory (dex-tro-rota-tory) and have a + rotational value (d +) ndash In Latin dexter means ldquoright siderdquo
Enantiomers that rotate polarized light in an anti-clockwise direction are said to be laevorotatory (lay-vo-rota-tory) and have a ndash rotational value (l -) ndash In Latin laevus means ldquoleft siderdquo
There are two systems used to provide specific names to each enantiomeric form
Stereochemistry in Food Older system used for naming sugars and amino
acids Enantiomeric forms are labeled ldquoLrdquo and ldquoDrdquo
Again Laevus for left and Dexter for right Based off a compound called glyceraldehyde
chiral carbon
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Shelf Life Termination
Shelf Life Shelf life is prolonged by hindering spoilage
processes Packaging
Opaque or darkened packages block light Can be gas impermeable to limit exposure to oxygen and water Can be filled with inert gases or vacuum packed (no gases)
Storage Low temperatures slow harmful reactions Smoking or drying foods removes water and hinder microbial
growth Additives
Salt or sugar added to remove water and hinder microbial growth
KNO3 or NaNO3 salts are reducing agents and can prevent harmful oxidation reactions
Anti-microbial agents Pickling - Organic acids and their salts (ex benzoic acid and
benzoate salts) make pH unfavorable for microbial growth Fermentation ndash production of alcohol hinders microbial growth
Shelf Life Antioxidants delay oxidative degradation
processes by reacting with oxygen to contain free radical formation Can occur naturally
Vitamin C (ascorbic acid) ndash citrus and green vegetables Vitamin E (tocopherol) ndash nuts seeds grains canola oil Beta-carotene ndash carrots broccoli tomatoes peaches Selenium ndash shellfish meat eggs grains Foods high in natural antioxidants green tea blueberries
cranberries dark chocolate turmeric oregano Can be synthetic additives but may have harmful
side effects BHA BHT PG THBP TBHQ
these are all based around a phenol
groupwhich is not
necessarily found in natural
antioxidants
(Full structures in
data booklet)
Shelf Life Types of antioxidants
Free radical quenchers React with radicals to produce less reactive radicals (HA =
quencher)R-O-O + HA R-O-O-H + A
Chelating agents Form very stable complex ions with transition metals (which
can produce radicals) Found naturally in rosemary tea and mustard Salts of the organic acid EDTA are added as artificial chelating
agents Reducing agents
React with oxygen or hydroperoxides Vitamin C or carotenoids are natural reducing agents
Color Foods are colored by either pigments or dyes
Pigments occur naturally Dyes are added artificially and must be tested for
safety Dyes or pigments will absorb a range of light
frequencies and reflect others The color we see in a dye or pigment is the result of
the colors of light reflected not absorbed Ex chlorophyll in green leaf vegetables absorbs red
and blue light reflecting green Molecular structures all involve extensive
delocalized pi bonding (shown on next slide) This system of delocalized pi bonding (conjugated
system) is responsible for the color we see
Color Some of the most common natural pigment
groups are Anthocyanins
Ex Cyanidin Carotenoids
Ex Beta-carotene Chlorophyll
Ex Chlorophyll-A Heme
Ex Heme B group
heme B groupchlorophyll-A
cyanidin
β-carotene
Color Anthocyanins
Responsible for reds pinks blues in berries beets flowers (Flavonones which give color to red grapes and berries are closely related to anthocyanins)
3-ring structures with varying numbers of OH groups in varying positions
Structure and therefore color is related to pH
predominantly red at low pH (acidic) blue at high pH (basic) and colorlesspale yellow at neutral pH
Temperature May break down at high temperatures and cause browning
Exposure to metal Form complexes with iron and aluminum and can change color
Color also affected when anthocyanins bond to sugars
Color Color of anthocyanins is pH dependent (they are
acidbase indicators)
Color Carotenes
Responsible for orange yellow and red colors in foods like carrots bananas tomatoes and saffron
Characterized by long hydrocarbon chains that often have carbon rings on the ends
Have nutritional value precursors to vitamin A (important in vision) act as antioxidants
Relatively stable during food processing but presence of C=C double bonds in hydrocarbon chain opens them up to oxidative degradation as seen in fats
Causes discoloration Prevents carotenoids from being able to be converted to
vitamin A
Color
β-carotene
Color Astaxanthin is a red pigment similar to
carotenoids found in lobster crab and salmon Bonds to proteins in the live animal and gives a
bluegreen color When heated bond to protein is broken which modifies
the structure and frequency of light absorbed appears bright red
Also an antioxidant
Color Chlorophyll
Green pigment responsible for plant photosynthesis Found in green vegetables Structure is centered around a porphyrin ring ndash a
planar ring system with 4 nitrogen atoms surrounding a central metal atom (magnesium in the case of chlorophyll)
Two forms chlorophyll A and chlorophyll B In chlorophyll B an aldehyde side chain replaces a
methyl side chain When cooked plant cells release acids
Causes an H+ ion to replace magnesium atom in center of structure causing a color change to an olivebrown
Opens the possibility for photodegradation (breakdown by light)
Color
chlorophyll A
(replaced with an aldehyde in chlorophyll B)
Color Heme
Pigment found in red blood cells Structure is similar to chlorophyll but there is an iron
atom in the center of the porphyrin ring Found in the protein myoglobin responsible for
oxygen transport Bright red when bound to oxygen but slow process
of autoxidation converts iron from +2 to +3 changing color to brown (less desirable) (myoglobin metmyoglobin)
Color change can be prevented by vacuum packing or packing with an inert gas like CO2
Color
heme groupin myoglobin
Color Color in foods is a result of the structures seen in
anthocyanins carotenoids chlorophylls and hemes All of these structures include an extensive network of
delocalized pi-bonds Alternating single and double bonds is called a conjugated
system The greater the extent of pi bond delocalization the closer
together in energy bonding and antibonding orbitals become All molecules absorb light energy as it promotes e-s between
molecular orbitals (bonding and antibonding orbitals) ndash energy required is proportional to distance between orbitals (less distance = less energy)
As orbitals are close together in a conjugated system low energy light (in the visible region) is absorbed for e- promotion
Color in these groups is the product of visible light absorption - color we see is complementary to the color(s) absorbed
Molecules without an extensive delocalized pi bond network (conjugated system) lack color as orbitals are further apart and only higher energy light promotes e-s (ex the anthocyanin carbinol)
Color Some pigments are water soluble because the
structures contain a large amount of -OH groups (H-bonding) Anthocyanins
Some pigments are fat soluble (ie not water soluble) because their structures contain little or no -OH groups (no H-bonding) carotenoids
Color
Many synthetic dyes are biochemically active and could be potentially harmful
Short-term toxicity easy to test and categorize but long-term effects are more difficult to study
Use of dyes in foods must be regulated but regulations are not standardized internationally posing issues in trade
Color Cooking foods often leads to browning
Two processes responsible Maillard reactions ndash combination of sugars and
proteins Caramelization ndash dehydration of sugar
Both involve removal of water molecule(s)
Color Maillard reactions
Sugars and proteins within the food combine in a condensation reaction
Aldehyde group in sugar (O atom) combines with amino group in protein (2 H atoms)
Initial condensation products polymerize to form brown-colored melanoidins
Maillard reactions only happen gt 140deg C Rate depends on amino acid present (ex lysine
reacts faster than cysteine)
initialcondensationproduct
Color Caramelization
Happens in foods high in carbohydrates Sugars dehydrate (lose H2O) at high temperatures
leaving behind C (dark brown color)
Browning intensifies the longer food is cooked eventually burning it (pure carbon is black)
Rate depends on Sugar type (fructose in fruits caramelizes very quickly) pH ndash extremes (high and low) promote caramelization
Genetically Modified Foods
Produced when organisms with modified DNA are used in food production Used to
Provide pest or disease resistance Bt corn contains toxin from bacillis thuringiensis that kills
insect pests Fungal-resistant potatoes Nematode-resistant bananas (nematode = worm)
Improve quality and range of crop Development of higher-yielding rice varieties Development of corn that can grow in dryer environments
Produce medicines or other products in large quantities Use of chickens that have been modified to lay eggs
containing human interferon (combats tumors and viruses) Use of cows to produce milk rich in omega-3 fatty acids
(polyunsaturated fats essential to growth development brain function)
Moth larva
Genetically Modified Foods
Drawbacks Are GM foods safe Will GM food production alter the natural ecosystem Do we understand enough about genetic
modification GM foods
Can cause allergic reactions in some people Have a slightly different composition from natural foods ndash
alters diet Produce altered pollen ndash might escape and cross with natural
species Long-term effects might be catastrophic unknown so far
Texture Food texture is related to physical properties
Hardness Elasticity Viscosity
These properties can be altered by Cooking Use of dispersed systems
Dispersed system = a stabilized macroscopically homogeneous mixture of two immiscible phases
(this means two substances that would not ordinarily mix ldquoappear tordquo on a macroscopic level (although at the molecular level they are still separate)
Texture Many types of dispersed systems name depends on
the physical states of the substances mixed LiquidSolid or SolidLiquid
Solid particles suspended in a liquid is called a suspension
Ex Blood (blood cells suspended in plasma) Liquid dispersed throughout a solid medium is called a
gel Ex Fruit Jelly (water trapped in a solid protein matrix)
LiquidLiquid Stable blend of two liquids that donrsquot mix is called an
emulsion Ex Mayonaisse (oil droplets suspended in aqueous system)
LiquidGas or GasLiquid Gas bubbles trapped in liquid medium is called a foam
Ex Whipped cream or egg whites Liquid droplets suspended in gas are called aerosols
Ex Aromas from food carried through the air
Texture Dispersed systems will slowly separate over
time Separation can be slowed by adding emulsifiers
Emulsifiers are stabilizers used to keep immiscible substance together
Have surfactant capability (can bind to both substances in suspension)
Similar to micelles in the action of soaps
Ex Lecithin Found commonly in egg
yolks One end is highly charged
and water soluble (bonds toaqueous phase) the otheris not (bonds to non-aqueous phase)
Texture Lecithin in mayonnaise
Lecithin is the emulsifier Mayonnaise made by beating eggs with
vinegar and oil Lecithin is found in eggs ndash charged
hydrophilic end bonds well to vinegar uncharged hydrophobic end bonds to oil
Vigorous beating produces many small oil droplets maximizing surface area for lecithin to act on and produce a stable emulsion
Stabilizers like sodium phosphate or metals are added to prevent separation (chefs use metal bowls)
hydrophilic
hydrophobic
Stereochemistry in Food Many food-specific compounds have a chiral
carbon atom and thus exist as two different enantiomers (optical isomers) Optical isomers are mirror images of one another ldquoOptical activityrdquo refers to the fact that the two mirror
image isomers rotate the direction of plane-polarized light in opposite directions
Enantiomers that rotate polarized light in a clockwise direction are said to be dextrorotatory (dex-tro-rota-tory) and have a + rotational value (d +) ndash In Latin dexter means ldquoright siderdquo
Enantiomers that rotate polarized light in an anti-clockwise direction are said to be laevorotatory (lay-vo-rota-tory) and have a ndash rotational value (l -) ndash In Latin laevus means ldquoleft siderdquo
There are two systems used to provide specific names to each enantiomeric form
Stereochemistry in Food Older system used for naming sugars and amino
acids Enantiomeric forms are labeled ldquoLrdquo and ldquoDrdquo
Again Laevus for left and Dexter for right Based off a compound called glyceraldehyde
chiral carbon
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Shelf Life Shelf life is prolonged by hindering spoilage
processes Packaging
Opaque or darkened packages block light Can be gas impermeable to limit exposure to oxygen and water Can be filled with inert gases or vacuum packed (no gases)
Storage Low temperatures slow harmful reactions Smoking or drying foods removes water and hinder microbial
growth Additives
Salt or sugar added to remove water and hinder microbial growth
KNO3 or NaNO3 salts are reducing agents and can prevent harmful oxidation reactions
Anti-microbial agents Pickling - Organic acids and their salts (ex benzoic acid and
benzoate salts) make pH unfavorable for microbial growth Fermentation ndash production of alcohol hinders microbial growth
Shelf Life Antioxidants delay oxidative degradation
processes by reacting with oxygen to contain free radical formation Can occur naturally
Vitamin C (ascorbic acid) ndash citrus and green vegetables Vitamin E (tocopherol) ndash nuts seeds grains canola oil Beta-carotene ndash carrots broccoli tomatoes peaches Selenium ndash shellfish meat eggs grains Foods high in natural antioxidants green tea blueberries
cranberries dark chocolate turmeric oregano Can be synthetic additives but may have harmful
side effects BHA BHT PG THBP TBHQ
these are all based around a phenol
groupwhich is not
necessarily found in natural
antioxidants
(Full structures in
data booklet)
Shelf Life Types of antioxidants
Free radical quenchers React with radicals to produce less reactive radicals (HA =
quencher)R-O-O + HA R-O-O-H + A
Chelating agents Form very stable complex ions with transition metals (which
can produce radicals) Found naturally in rosemary tea and mustard Salts of the organic acid EDTA are added as artificial chelating
agents Reducing agents
React with oxygen or hydroperoxides Vitamin C or carotenoids are natural reducing agents
Color Foods are colored by either pigments or dyes
Pigments occur naturally Dyes are added artificially and must be tested for
safety Dyes or pigments will absorb a range of light
frequencies and reflect others The color we see in a dye or pigment is the result of
the colors of light reflected not absorbed Ex chlorophyll in green leaf vegetables absorbs red
and blue light reflecting green Molecular structures all involve extensive
delocalized pi bonding (shown on next slide) This system of delocalized pi bonding (conjugated
system) is responsible for the color we see
Color Some of the most common natural pigment
groups are Anthocyanins
Ex Cyanidin Carotenoids
Ex Beta-carotene Chlorophyll
Ex Chlorophyll-A Heme
Ex Heme B group
heme B groupchlorophyll-A
cyanidin
β-carotene
Color Anthocyanins
Responsible for reds pinks blues in berries beets flowers (Flavonones which give color to red grapes and berries are closely related to anthocyanins)
3-ring structures with varying numbers of OH groups in varying positions
Structure and therefore color is related to pH
predominantly red at low pH (acidic) blue at high pH (basic) and colorlesspale yellow at neutral pH
Temperature May break down at high temperatures and cause browning
Exposure to metal Form complexes with iron and aluminum and can change color
Color also affected when anthocyanins bond to sugars
Color Color of anthocyanins is pH dependent (they are
acidbase indicators)
Color Carotenes
Responsible for orange yellow and red colors in foods like carrots bananas tomatoes and saffron
Characterized by long hydrocarbon chains that often have carbon rings on the ends
Have nutritional value precursors to vitamin A (important in vision) act as antioxidants
Relatively stable during food processing but presence of C=C double bonds in hydrocarbon chain opens them up to oxidative degradation as seen in fats
Causes discoloration Prevents carotenoids from being able to be converted to
vitamin A
Color
β-carotene
Color Astaxanthin is a red pigment similar to
carotenoids found in lobster crab and salmon Bonds to proteins in the live animal and gives a
bluegreen color When heated bond to protein is broken which modifies
the structure and frequency of light absorbed appears bright red
Also an antioxidant
Color Chlorophyll
Green pigment responsible for plant photosynthesis Found in green vegetables Structure is centered around a porphyrin ring ndash a
planar ring system with 4 nitrogen atoms surrounding a central metal atom (magnesium in the case of chlorophyll)
Two forms chlorophyll A and chlorophyll B In chlorophyll B an aldehyde side chain replaces a
methyl side chain When cooked plant cells release acids
Causes an H+ ion to replace magnesium atom in center of structure causing a color change to an olivebrown
Opens the possibility for photodegradation (breakdown by light)
Color
chlorophyll A
(replaced with an aldehyde in chlorophyll B)
Color Heme
Pigment found in red blood cells Structure is similar to chlorophyll but there is an iron
atom in the center of the porphyrin ring Found in the protein myoglobin responsible for
oxygen transport Bright red when bound to oxygen but slow process
of autoxidation converts iron from +2 to +3 changing color to brown (less desirable) (myoglobin metmyoglobin)
Color change can be prevented by vacuum packing or packing with an inert gas like CO2
Color
heme groupin myoglobin
Color Color in foods is a result of the structures seen in
anthocyanins carotenoids chlorophylls and hemes All of these structures include an extensive network of
delocalized pi-bonds Alternating single and double bonds is called a conjugated
system The greater the extent of pi bond delocalization the closer
together in energy bonding and antibonding orbitals become All molecules absorb light energy as it promotes e-s between
molecular orbitals (bonding and antibonding orbitals) ndash energy required is proportional to distance between orbitals (less distance = less energy)
As orbitals are close together in a conjugated system low energy light (in the visible region) is absorbed for e- promotion
Color in these groups is the product of visible light absorption - color we see is complementary to the color(s) absorbed
Molecules without an extensive delocalized pi bond network (conjugated system) lack color as orbitals are further apart and only higher energy light promotes e-s (ex the anthocyanin carbinol)
Color Some pigments are water soluble because the
structures contain a large amount of -OH groups (H-bonding) Anthocyanins
Some pigments are fat soluble (ie not water soluble) because their structures contain little or no -OH groups (no H-bonding) carotenoids
Color
Many synthetic dyes are biochemically active and could be potentially harmful
Short-term toxicity easy to test and categorize but long-term effects are more difficult to study
Use of dyes in foods must be regulated but regulations are not standardized internationally posing issues in trade
Color Cooking foods often leads to browning
Two processes responsible Maillard reactions ndash combination of sugars and
proteins Caramelization ndash dehydration of sugar
Both involve removal of water molecule(s)
Color Maillard reactions
Sugars and proteins within the food combine in a condensation reaction
Aldehyde group in sugar (O atom) combines with amino group in protein (2 H atoms)
Initial condensation products polymerize to form brown-colored melanoidins
Maillard reactions only happen gt 140deg C Rate depends on amino acid present (ex lysine
reacts faster than cysteine)
initialcondensationproduct
Color Caramelization
Happens in foods high in carbohydrates Sugars dehydrate (lose H2O) at high temperatures
leaving behind C (dark brown color)
Browning intensifies the longer food is cooked eventually burning it (pure carbon is black)
Rate depends on Sugar type (fructose in fruits caramelizes very quickly) pH ndash extremes (high and low) promote caramelization
Genetically Modified Foods
Produced when organisms with modified DNA are used in food production Used to
Provide pest or disease resistance Bt corn contains toxin from bacillis thuringiensis that kills
insect pests Fungal-resistant potatoes Nematode-resistant bananas (nematode = worm)
Improve quality and range of crop Development of higher-yielding rice varieties Development of corn that can grow in dryer environments
Produce medicines or other products in large quantities Use of chickens that have been modified to lay eggs
containing human interferon (combats tumors and viruses) Use of cows to produce milk rich in omega-3 fatty acids
(polyunsaturated fats essential to growth development brain function)
Moth larva
Genetically Modified Foods
Drawbacks Are GM foods safe Will GM food production alter the natural ecosystem Do we understand enough about genetic
modification GM foods
Can cause allergic reactions in some people Have a slightly different composition from natural foods ndash
alters diet Produce altered pollen ndash might escape and cross with natural
species Long-term effects might be catastrophic unknown so far
Texture Food texture is related to physical properties
Hardness Elasticity Viscosity
These properties can be altered by Cooking Use of dispersed systems
Dispersed system = a stabilized macroscopically homogeneous mixture of two immiscible phases
(this means two substances that would not ordinarily mix ldquoappear tordquo on a macroscopic level (although at the molecular level they are still separate)
Texture Many types of dispersed systems name depends on
the physical states of the substances mixed LiquidSolid or SolidLiquid
Solid particles suspended in a liquid is called a suspension
Ex Blood (blood cells suspended in plasma) Liquid dispersed throughout a solid medium is called a
gel Ex Fruit Jelly (water trapped in a solid protein matrix)
LiquidLiquid Stable blend of two liquids that donrsquot mix is called an
emulsion Ex Mayonaisse (oil droplets suspended in aqueous system)
LiquidGas or GasLiquid Gas bubbles trapped in liquid medium is called a foam
Ex Whipped cream or egg whites Liquid droplets suspended in gas are called aerosols
Ex Aromas from food carried through the air
Texture Dispersed systems will slowly separate over
time Separation can be slowed by adding emulsifiers
Emulsifiers are stabilizers used to keep immiscible substance together
Have surfactant capability (can bind to both substances in suspension)
Similar to micelles in the action of soaps
Ex Lecithin Found commonly in egg
yolks One end is highly charged
and water soluble (bonds toaqueous phase) the otheris not (bonds to non-aqueous phase)
Texture Lecithin in mayonnaise
Lecithin is the emulsifier Mayonnaise made by beating eggs with
vinegar and oil Lecithin is found in eggs ndash charged
hydrophilic end bonds well to vinegar uncharged hydrophobic end bonds to oil
Vigorous beating produces many small oil droplets maximizing surface area for lecithin to act on and produce a stable emulsion
Stabilizers like sodium phosphate or metals are added to prevent separation (chefs use metal bowls)
hydrophilic
hydrophobic
Stereochemistry in Food Many food-specific compounds have a chiral
carbon atom and thus exist as two different enantiomers (optical isomers) Optical isomers are mirror images of one another ldquoOptical activityrdquo refers to the fact that the two mirror
image isomers rotate the direction of plane-polarized light in opposite directions
Enantiomers that rotate polarized light in a clockwise direction are said to be dextrorotatory (dex-tro-rota-tory) and have a + rotational value (d +) ndash In Latin dexter means ldquoright siderdquo
Enantiomers that rotate polarized light in an anti-clockwise direction are said to be laevorotatory (lay-vo-rota-tory) and have a ndash rotational value (l -) ndash In Latin laevus means ldquoleft siderdquo
There are two systems used to provide specific names to each enantiomeric form
Stereochemistry in Food Older system used for naming sugars and amino
acids Enantiomeric forms are labeled ldquoLrdquo and ldquoDrdquo
Again Laevus for left and Dexter for right Based off a compound called glyceraldehyde
chiral carbon
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Shelf Life Antioxidants delay oxidative degradation
processes by reacting with oxygen to contain free radical formation Can occur naturally
Vitamin C (ascorbic acid) ndash citrus and green vegetables Vitamin E (tocopherol) ndash nuts seeds grains canola oil Beta-carotene ndash carrots broccoli tomatoes peaches Selenium ndash shellfish meat eggs grains Foods high in natural antioxidants green tea blueberries
cranberries dark chocolate turmeric oregano Can be synthetic additives but may have harmful
side effects BHA BHT PG THBP TBHQ
these are all based around a phenol
groupwhich is not
necessarily found in natural
antioxidants
(Full structures in
data booklet)
Shelf Life Types of antioxidants
Free radical quenchers React with radicals to produce less reactive radicals (HA =
quencher)R-O-O + HA R-O-O-H + A
Chelating agents Form very stable complex ions with transition metals (which
can produce radicals) Found naturally in rosemary tea and mustard Salts of the organic acid EDTA are added as artificial chelating
agents Reducing agents
React with oxygen or hydroperoxides Vitamin C or carotenoids are natural reducing agents
Color Foods are colored by either pigments or dyes
Pigments occur naturally Dyes are added artificially and must be tested for
safety Dyes or pigments will absorb a range of light
frequencies and reflect others The color we see in a dye or pigment is the result of
the colors of light reflected not absorbed Ex chlorophyll in green leaf vegetables absorbs red
and blue light reflecting green Molecular structures all involve extensive
delocalized pi bonding (shown on next slide) This system of delocalized pi bonding (conjugated
system) is responsible for the color we see
Color Some of the most common natural pigment
groups are Anthocyanins
Ex Cyanidin Carotenoids
Ex Beta-carotene Chlorophyll
Ex Chlorophyll-A Heme
Ex Heme B group
heme B groupchlorophyll-A
cyanidin
β-carotene
Color Anthocyanins
Responsible for reds pinks blues in berries beets flowers (Flavonones which give color to red grapes and berries are closely related to anthocyanins)
3-ring structures with varying numbers of OH groups in varying positions
Structure and therefore color is related to pH
predominantly red at low pH (acidic) blue at high pH (basic) and colorlesspale yellow at neutral pH
Temperature May break down at high temperatures and cause browning
Exposure to metal Form complexes with iron and aluminum and can change color
Color also affected when anthocyanins bond to sugars
Color Color of anthocyanins is pH dependent (they are
acidbase indicators)
Color Carotenes
Responsible for orange yellow and red colors in foods like carrots bananas tomatoes and saffron
Characterized by long hydrocarbon chains that often have carbon rings on the ends
Have nutritional value precursors to vitamin A (important in vision) act as antioxidants
Relatively stable during food processing but presence of C=C double bonds in hydrocarbon chain opens them up to oxidative degradation as seen in fats
Causes discoloration Prevents carotenoids from being able to be converted to
vitamin A
Color
β-carotene
Color Astaxanthin is a red pigment similar to
carotenoids found in lobster crab and salmon Bonds to proteins in the live animal and gives a
bluegreen color When heated bond to protein is broken which modifies
the structure and frequency of light absorbed appears bright red
Also an antioxidant
Color Chlorophyll
Green pigment responsible for plant photosynthesis Found in green vegetables Structure is centered around a porphyrin ring ndash a
planar ring system with 4 nitrogen atoms surrounding a central metal atom (magnesium in the case of chlorophyll)
Two forms chlorophyll A and chlorophyll B In chlorophyll B an aldehyde side chain replaces a
methyl side chain When cooked plant cells release acids
Causes an H+ ion to replace magnesium atom in center of structure causing a color change to an olivebrown
Opens the possibility for photodegradation (breakdown by light)
Color
chlorophyll A
(replaced with an aldehyde in chlorophyll B)
Color Heme
Pigment found in red blood cells Structure is similar to chlorophyll but there is an iron
atom in the center of the porphyrin ring Found in the protein myoglobin responsible for
oxygen transport Bright red when bound to oxygen but slow process
of autoxidation converts iron from +2 to +3 changing color to brown (less desirable) (myoglobin metmyoglobin)
Color change can be prevented by vacuum packing or packing with an inert gas like CO2
Color
heme groupin myoglobin
Color Color in foods is a result of the structures seen in
anthocyanins carotenoids chlorophylls and hemes All of these structures include an extensive network of
delocalized pi-bonds Alternating single and double bonds is called a conjugated
system The greater the extent of pi bond delocalization the closer
together in energy bonding and antibonding orbitals become All molecules absorb light energy as it promotes e-s between
molecular orbitals (bonding and antibonding orbitals) ndash energy required is proportional to distance between orbitals (less distance = less energy)
As orbitals are close together in a conjugated system low energy light (in the visible region) is absorbed for e- promotion
Color in these groups is the product of visible light absorption - color we see is complementary to the color(s) absorbed
Molecules without an extensive delocalized pi bond network (conjugated system) lack color as orbitals are further apart and only higher energy light promotes e-s (ex the anthocyanin carbinol)
Color Some pigments are water soluble because the
structures contain a large amount of -OH groups (H-bonding) Anthocyanins
Some pigments are fat soluble (ie not water soluble) because their structures contain little or no -OH groups (no H-bonding) carotenoids
Color
Many synthetic dyes are biochemically active and could be potentially harmful
Short-term toxicity easy to test and categorize but long-term effects are more difficult to study
Use of dyes in foods must be regulated but regulations are not standardized internationally posing issues in trade
Color Cooking foods often leads to browning
Two processes responsible Maillard reactions ndash combination of sugars and
proteins Caramelization ndash dehydration of sugar
Both involve removal of water molecule(s)
Color Maillard reactions
Sugars and proteins within the food combine in a condensation reaction
Aldehyde group in sugar (O atom) combines with amino group in protein (2 H atoms)
Initial condensation products polymerize to form brown-colored melanoidins
Maillard reactions only happen gt 140deg C Rate depends on amino acid present (ex lysine
reacts faster than cysteine)
initialcondensationproduct
Color Caramelization
Happens in foods high in carbohydrates Sugars dehydrate (lose H2O) at high temperatures
leaving behind C (dark brown color)
Browning intensifies the longer food is cooked eventually burning it (pure carbon is black)
Rate depends on Sugar type (fructose in fruits caramelizes very quickly) pH ndash extremes (high and low) promote caramelization
Genetically Modified Foods
Produced when organisms with modified DNA are used in food production Used to
Provide pest or disease resistance Bt corn contains toxin from bacillis thuringiensis that kills
insect pests Fungal-resistant potatoes Nematode-resistant bananas (nematode = worm)
Improve quality and range of crop Development of higher-yielding rice varieties Development of corn that can grow in dryer environments
Produce medicines or other products in large quantities Use of chickens that have been modified to lay eggs
containing human interferon (combats tumors and viruses) Use of cows to produce milk rich in omega-3 fatty acids
(polyunsaturated fats essential to growth development brain function)
Moth larva
Genetically Modified Foods
Drawbacks Are GM foods safe Will GM food production alter the natural ecosystem Do we understand enough about genetic
modification GM foods
Can cause allergic reactions in some people Have a slightly different composition from natural foods ndash
alters diet Produce altered pollen ndash might escape and cross with natural
species Long-term effects might be catastrophic unknown so far
Texture Food texture is related to physical properties
Hardness Elasticity Viscosity
These properties can be altered by Cooking Use of dispersed systems
Dispersed system = a stabilized macroscopically homogeneous mixture of two immiscible phases
(this means two substances that would not ordinarily mix ldquoappear tordquo on a macroscopic level (although at the molecular level they are still separate)
Texture Many types of dispersed systems name depends on
the physical states of the substances mixed LiquidSolid or SolidLiquid
Solid particles suspended in a liquid is called a suspension
Ex Blood (blood cells suspended in plasma) Liquid dispersed throughout a solid medium is called a
gel Ex Fruit Jelly (water trapped in a solid protein matrix)
LiquidLiquid Stable blend of two liquids that donrsquot mix is called an
emulsion Ex Mayonaisse (oil droplets suspended in aqueous system)
LiquidGas or GasLiquid Gas bubbles trapped in liquid medium is called a foam
Ex Whipped cream or egg whites Liquid droplets suspended in gas are called aerosols
Ex Aromas from food carried through the air
Texture Dispersed systems will slowly separate over
time Separation can be slowed by adding emulsifiers
Emulsifiers are stabilizers used to keep immiscible substance together
Have surfactant capability (can bind to both substances in suspension)
Similar to micelles in the action of soaps
Ex Lecithin Found commonly in egg
yolks One end is highly charged
and water soluble (bonds toaqueous phase) the otheris not (bonds to non-aqueous phase)
Texture Lecithin in mayonnaise
Lecithin is the emulsifier Mayonnaise made by beating eggs with
vinegar and oil Lecithin is found in eggs ndash charged
hydrophilic end bonds well to vinegar uncharged hydrophobic end bonds to oil
Vigorous beating produces many small oil droplets maximizing surface area for lecithin to act on and produce a stable emulsion
Stabilizers like sodium phosphate or metals are added to prevent separation (chefs use metal bowls)
hydrophilic
hydrophobic
Stereochemistry in Food Many food-specific compounds have a chiral
carbon atom and thus exist as two different enantiomers (optical isomers) Optical isomers are mirror images of one another ldquoOptical activityrdquo refers to the fact that the two mirror
image isomers rotate the direction of plane-polarized light in opposite directions
Enantiomers that rotate polarized light in a clockwise direction are said to be dextrorotatory (dex-tro-rota-tory) and have a + rotational value (d +) ndash In Latin dexter means ldquoright siderdquo
Enantiomers that rotate polarized light in an anti-clockwise direction are said to be laevorotatory (lay-vo-rota-tory) and have a ndash rotational value (l -) ndash In Latin laevus means ldquoleft siderdquo
There are two systems used to provide specific names to each enantiomeric form
Stereochemistry in Food Older system used for naming sugars and amino
acids Enantiomeric forms are labeled ldquoLrdquo and ldquoDrdquo
Again Laevus for left and Dexter for right Based off a compound called glyceraldehyde
chiral carbon
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Shelf Life Types of antioxidants
Free radical quenchers React with radicals to produce less reactive radicals (HA =
quencher)R-O-O + HA R-O-O-H + A
Chelating agents Form very stable complex ions with transition metals (which
can produce radicals) Found naturally in rosemary tea and mustard Salts of the organic acid EDTA are added as artificial chelating
agents Reducing agents
React with oxygen or hydroperoxides Vitamin C or carotenoids are natural reducing agents
Color Foods are colored by either pigments or dyes
Pigments occur naturally Dyes are added artificially and must be tested for
safety Dyes or pigments will absorb a range of light
frequencies and reflect others The color we see in a dye or pigment is the result of
the colors of light reflected not absorbed Ex chlorophyll in green leaf vegetables absorbs red
and blue light reflecting green Molecular structures all involve extensive
delocalized pi bonding (shown on next slide) This system of delocalized pi bonding (conjugated
system) is responsible for the color we see
Color Some of the most common natural pigment
groups are Anthocyanins
Ex Cyanidin Carotenoids
Ex Beta-carotene Chlorophyll
Ex Chlorophyll-A Heme
Ex Heme B group
heme B groupchlorophyll-A
cyanidin
β-carotene
Color Anthocyanins
Responsible for reds pinks blues in berries beets flowers (Flavonones which give color to red grapes and berries are closely related to anthocyanins)
3-ring structures with varying numbers of OH groups in varying positions
Structure and therefore color is related to pH
predominantly red at low pH (acidic) blue at high pH (basic) and colorlesspale yellow at neutral pH
Temperature May break down at high temperatures and cause browning
Exposure to metal Form complexes with iron and aluminum and can change color
Color also affected when anthocyanins bond to sugars
Color Color of anthocyanins is pH dependent (they are
acidbase indicators)
Color Carotenes
Responsible for orange yellow and red colors in foods like carrots bananas tomatoes and saffron
Characterized by long hydrocarbon chains that often have carbon rings on the ends
Have nutritional value precursors to vitamin A (important in vision) act as antioxidants
Relatively stable during food processing but presence of C=C double bonds in hydrocarbon chain opens them up to oxidative degradation as seen in fats
Causes discoloration Prevents carotenoids from being able to be converted to
vitamin A
Color
β-carotene
Color Astaxanthin is a red pigment similar to
carotenoids found in lobster crab and salmon Bonds to proteins in the live animal and gives a
bluegreen color When heated bond to protein is broken which modifies
the structure and frequency of light absorbed appears bright red
Also an antioxidant
Color Chlorophyll
Green pigment responsible for plant photosynthesis Found in green vegetables Structure is centered around a porphyrin ring ndash a
planar ring system with 4 nitrogen atoms surrounding a central metal atom (magnesium in the case of chlorophyll)
Two forms chlorophyll A and chlorophyll B In chlorophyll B an aldehyde side chain replaces a
methyl side chain When cooked plant cells release acids
Causes an H+ ion to replace magnesium atom in center of structure causing a color change to an olivebrown
Opens the possibility for photodegradation (breakdown by light)
Color
chlorophyll A
(replaced with an aldehyde in chlorophyll B)
Color Heme
Pigment found in red blood cells Structure is similar to chlorophyll but there is an iron
atom in the center of the porphyrin ring Found in the protein myoglobin responsible for
oxygen transport Bright red when bound to oxygen but slow process
of autoxidation converts iron from +2 to +3 changing color to brown (less desirable) (myoglobin metmyoglobin)
Color change can be prevented by vacuum packing or packing with an inert gas like CO2
Color
heme groupin myoglobin
Color Color in foods is a result of the structures seen in
anthocyanins carotenoids chlorophylls and hemes All of these structures include an extensive network of
delocalized pi-bonds Alternating single and double bonds is called a conjugated
system The greater the extent of pi bond delocalization the closer
together in energy bonding and antibonding orbitals become All molecules absorb light energy as it promotes e-s between
molecular orbitals (bonding and antibonding orbitals) ndash energy required is proportional to distance between orbitals (less distance = less energy)
As orbitals are close together in a conjugated system low energy light (in the visible region) is absorbed for e- promotion
Color in these groups is the product of visible light absorption - color we see is complementary to the color(s) absorbed
Molecules without an extensive delocalized pi bond network (conjugated system) lack color as orbitals are further apart and only higher energy light promotes e-s (ex the anthocyanin carbinol)
Color Some pigments are water soluble because the
structures contain a large amount of -OH groups (H-bonding) Anthocyanins
Some pigments are fat soluble (ie not water soluble) because their structures contain little or no -OH groups (no H-bonding) carotenoids
Color
Many synthetic dyes are biochemically active and could be potentially harmful
Short-term toxicity easy to test and categorize but long-term effects are more difficult to study
Use of dyes in foods must be regulated but regulations are not standardized internationally posing issues in trade
Color Cooking foods often leads to browning
Two processes responsible Maillard reactions ndash combination of sugars and
proteins Caramelization ndash dehydration of sugar
Both involve removal of water molecule(s)
Color Maillard reactions
Sugars and proteins within the food combine in a condensation reaction
Aldehyde group in sugar (O atom) combines with amino group in protein (2 H atoms)
Initial condensation products polymerize to form brown-colored melanoidins
Maillard reactions only happen gt 140deg C Rate depends on amino acid present (ex lysine
reacts faster than cysteine)
initialcondensationproduct
Color Caramelization
Happens in foods high in carbohydrates Sugars dehydrate (lose H2O) at high temperatures
leaving behind C (dark brown color)
Browning intensifies the longer food is cooked eventually burning it (pure carbon is black)
Rate depends on Sugar type (fructose in fruits caramelizes very quickly) pH ndash extremes (high and low) promote caramelization
Genetically Modified Foods
Produced when organisms with modified DNA are used in food production Used to
Provide pest or disease resistance Bt corn contains toxin from bacillis thuringiensis that kills
insect pests Fungal-resistant potatoes Nematode-resistant bananas (nematode = worm)
Improve quality and range of crop Development of higher-yielding rice varieties Development of corn that can grow in dryer environments
Produce medicines or other products in large quantities Use of chickens that have been modified to lay eggs
containing human interferon (combats tumors and viruses) Use of cows to produce milk rich in omega-3 fatty acids
(polyunsaturated fats essential to growth development brain function)
Moth larva
Genetically Modified Foods
Drawbacks Are GM foods safe Will GM food production alter the natural ecosystem Do we understand enough about genetic
modification GM foods
Can cause allergic reactions in some people Have a slightly different composition from natural foods ndash
alters diet Produce altered pollen ndash might escape and cross with natural
species Long-term effects might be catastrophic unknown so far
Texture Food texture is related to physical properties
Hardness Elasticity Viscosity
These properties can be altered by Cooking Use of dispersed systems
Dispersed system = a stabilized macroscopically homogeneous mixture of two immiscible phases
(this means two substances that would not ordinarily mix ldquoappear tordquo on a macroscopic level (although at the molecular level they are still separate)
Texture Many types of dispersed systems name depends on
the physical states of the substances mixed LiquidSolid or SolidLiquid
Solid particles suspended in a liquid is called a suspension
Ex Blood (blood cells suspended in plasma) Liquid dispersed throughout a solid medium is called a
gel Ex Fruit Jelly (water trapped in a solid protein matrix)
LiquidLiquid Stable blend of two liquids that donrsquot mix is called an
emulsion Ex Mayonaisse (oil droplets suspended in aqueous system)
LiquidGas or GasLiquid Gas bubbles trapped in liquid medium is called a foam
Ex Whipped cream or egg whites Liquid droplets suspended in gas are called aerosols
Ex Aromas from food carried through the air
Texture Dispersed systems will slowly separate over
time Separation can be slowed by adding emulsifiers
Emulsifiers are stabilizers used to keep immiscible substance together
Have surfactant capability (can bind to both substances in suspension)
Similar to micelles in the action of soaps
Ex Lecithin Found commonly in egg
yolks One end is highly charged
and water soluble (bonds toaqueous phase) the otheris not (bonds to non-aqueous phase)
Texture Lecithin in mayonnaise
Lecithin is the emulsifier Mayonnaise made by beating eggs with
vinegar and oil Lecithin is found in eggs ndash charged
hydrophilic end bonds well to vinegar uncharged hydrophobic end bonds to oil
Vigorous beating produces many small oil droplets maximizing surface area for lecithin to act on and produce a stable emulsion
Stabilizers like sodium phosphate or metals are added to prevent separation (chefs use metal bowls)
hydrophilic
hydrophobic
Stereochemistry in Food Many food-specific compounds have a chiral
carbon atom and thus exist as two different enantiomers (optical isomers) Optical isomers are mirror images of one another ldquoOptical activityrdquo refers to the fact that the two mirror
image isomers rotate the direction of plane-polarized light in opposite directions
Enantiomers that rotate polarized light in a clockwise direction are said to be dextrorotatory (dex-tro-rota-tory) and have a + rotational value (d +) ndash In Latin dexter means ldquoright siderdquo
Enantiomers that rotate polarized light in an anti-clockwise direction are said to be laevorotatory (lay-vo-rota-tory) and have a ndash rotational value (l -) ndash In Latin laevus means ldquoleft siderdquo
There are two systems used to provide specific names to each enantiomeric form
Stereochemistry in Food Older system used for naming sugars and amino
acids Enantiomeric forms are labeled ldquoLrdquo and ldquoDrdquo
Again Laevus for left and Dexter for right Based off a compound called glyceraldehyde
chiral carbon
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Color Foods are colored by either pigments or dyes
Pigments occur naturally Dyes are added artificially and must be tested for
safety Dyes or pigments will absorb a range of light
frequencies and reflect others The color we see in a dye or pigment is the result of
the colors of light reflected not absorbed Ex chlorophyll in green leaf vegetables absorbs red
and blue light reflecting green Molecular structures all involve extensive
delocalized pi bonding (shown on next slide) This system of delocalized pi bonding (conjugated
system) is responsible for the color we see
Color Some of the most common natural pigment
groups are Anthocyanins
Ex Cyanidin Carotenoids
Ex Beta-carotene Chlorophyll
Ex Chlorophyll-A Heme
Ex Heme B group
heme B groupchlorophyll-A
cyanidin
β-carotene
Color Anthocyanins
Responsible for reds pinks blues in berries beets flowers (Flavonones which give color to red grapes and berries are closely related to anthocyanins)
3-ring structures with varying numbers of OH groups in varying positions
Structure and therefore color is related to pH
predominantly red at low pH (acidic) blue at high pH (basic) and colorlesspale yellow at neutral pH
Temperature May break down at high temperatures and cause browning
Exposure to metal Form complexes with iron and aluminum and can change color
Color also affected when anthocyanins bond to sugars
Color Color of anthocyanins is pH dependent (they are
acidbase indicators)
Color Carotenes
Responsible for orange yellow and red colors in foods like carrots bananas tomatoes and saffron
Characterized by long hydrocarbon chains that often have carbon rings on the ends
Have nutritional value precursors to vitamin A (important in vision) act as antioxidants
Relatively stable during food processing but presence of C=C double bonds in hydrocarbon chain opens them up to oxidative degradation as seen in fats
Causes discoloration Prevents carotenoids from being able to be converted to
vitamin A
Color
β-carotene
Color Astaxanthin is a red pigment similar to
carotenoids found in lobster crab and salmon Bonds to proteins in the live animal and gives a
bluegreen color When heated bond to protein is broken which modifies
the structure and frequency of light absorbed appears bright red
Also an antioxidant
Color Chlorophyll
Green pigment responsible for plant photosynthesis Found in green vegetables Structure is centered around a porphyrin ring ndash a
planar ring system with 4 nitrogen atoms surrounding a central metal atom (magnesium in the case of chlorophyll)
Two forms chlorophyll A and chlorophyll B In chlorophyll B an aldehyde side chain replaces a
methyl side chain When cooked plant cells release acids
Causes an H+ ion to replace magnesium atom in center of structure causing a color change to an olivebrown
Opens the possibility for photodegradation (breakdown by light)
Color
chlorophyll A
(replaced with an aldehyde in chlorophyll B)
Color Heme
Pigment found in red blood cells Structure is similar to chlorophyll but there is an iron
atom in the center of the porphyrin ring Found in the protein myoglobin responsible for
oxygen transport Bright red when bound to oxygen but slow process
of autoxidation converts iron from +2 to +3 changing color to brown (less desirable) (myoglobin metmyoglobin)
Color change can be prevented by vacuum packing or packing with an inert gas like CO2
Color
heme groupin myoglobin
Color Color in foods is a result of the structures seen in
anthocyanins carotenoids chlorophylls and hemes All of these structures include an extensive network of
delocalized pi-bonds Alternating single and double bonds is called a conjugated
system The greater the extent of pi bond delocalization the closer
together in energy bonding and antibonding orbitals become All molecules absorb light energy as it promotes e-s between
molecular orbitals (bonding and antibonding orbitals) ndash energy required is proportional to distance between orbitals (less distance = less energy)
As orbitals are close together in a conjugated system low energy light (in the visible region) is absorbed for e- promotion
Color in these groups is the product of visible light absorption - color we see is complementary to the color(s) absorbed
Molecules without an extensive delocalized pi bond network (conjugated system) lack color as orbitals are further apart and only higher energy light promotes e-s (ex the anthocyanin carbinol)
Color Some pigments are water soluble because the
structures contain a large amount of -OH groups (H-bonding) Anthocyanins
Some pigments are fat soluble (ie not water soluble) because their structures contain little or no -OH groups (no H-bonding) carotenoids
Color
Many synthetic dyes are biochemically active and could be potentially harmful
Short-term toxicity easy to test and categorize but long-term effects are more difficult to study
Use of dyes in foods must be regulated but regulations are not standardized internationally posing issues in trade
Color Cooking foods often leads to browning
Two processes responsible Maillard reactions ndash combination of sugars and
proteins Caramelization ndash dehydration of sugar
Both involve removal of water molecule(s)
Color Maillard reactions
Sugars and proteins within the food combine in a condensation reaction
Aldehyde group in sugar (O atom) combines with amino group in protein (2 H atoms)
Initial condensation products polymerize to form brown-colored melanoidins
Maillard reactions only happen gt 140deg C Rate depends on amino acid present (ex lysine
reacts faster than cysteine)
initialcondensationproduct
Color Caramelization
Happens in foods high in carbohydrates Sugars dehydrate (lose H2O) at high temperatures
leaving behind C (dark brown color)
Browning intensifies the longer food is cooked eventually burning it (pure carbon is black)
Rate depends on Sugar type (fructose in fruits caramelizes very quickly) pH ndash extremes (high and low) promote caramelization
Genetically Modified Foods
Produced when organisms with modified DNA are used in food production Used to
Provide pest or disease resistance Bt corn contains toxin from bacillis thuringiensis that kills
insect pests Fungal-resistant potatoes Nematode-resistant bananas (nematode = worm)
Improve quality and range of crop Development of higher-yielding rice varieties Development of corn that can grow in dryer environments
Produce medicines or other products in large quantities Use of chickens that have been modified to lay eggs
containing human interferon (combats tumors and viruses) Use of cows to produce milk rich in omega-3 fatty acids
(polyunsaturated fats essential to growth development brain function)
Moth larva
Genetically Modified Foods
Drawbacks Are GM foods safe Will GM food production alter the natural ecosystem Do we understand enough about genetic
modification GM foods
Can cause allergic reactions in some people Have a slightly different composition from natural foods ndash
alters diet Produce altered pollen ndash might escape and cross with natural
species Long-term effects might be catastrophic unknown so far
Texture Food texture is related to physical properties
Hardness Elasticity Viscosity
These properties can be altered by Cooking Use of dispersed systems
Dispersed system = a stabilized macroscopically homogeneous mixture of two immiscible phases
(this means two substances that would not ordinarily mix ldquoappear tordquo on a macroscopic level (although at the molecular level they are still separate)
Texture Many types of dispersed systems name depends on
the physical states of the substances mixed LiquidSolid or SolidLiquid
Solid particles suspended in a liquid is called a suspension
Ex Blood (blood cells suspended in plasma) Liquid dispersed throughout a solid medium is called a
gel Ex Fruit Jelly (water trapped in a solid protein matrix)
LiquidLiquid Stable blend of two liquids that donrsquot mix is called an
emulsion Ex Mayonaisse (oil droplets suspended in aqueous system)
LiquidGas or GasLiquid Gas bubbles trapped in liquid medium is called a foam
Ex Whipped cream or egg whites Liquid droplets suspended in gas are called aerosols
Ex Aromas from food carried through the air
Texture Dispersed systems will slowly separate over
time Separation can be slowed by adding emulsifiers
Emulsifiers are stabilizers used to keep immiscible substance together
Have surfactant capability (can bind to both substances in suspension)
Similar to micelles in the action of soaps
Ex Lecithin Found commonly in egg
yolks One end is highly charged
and water soluble (bonds toaqueous phase) the otheris not (bonds to non-aqueous phase)
Texture Lecithin in mayonnaise
Lecithin is the emulsifier Mayonnaise made by beating eggs with
vinegar and oil Lecithin is found in eggs ndash charged
hydrophilic end bonds well to vinegar uncharged hydrophobic end bonds to oil
Vigorous beating produces many small oil droplets maximizing surface area for lecithin to act on and produce a stable emulsion
Stabilizers like sodium phosphate or metals are added to prevent separation (chefs use metal bowls)
hydrophilic
hydrophobic
Stereochemistry in Food Many food-specific compounds have a chiral
carbon atom and thus exist as two different enantiomers (optical isomers) Optical isomers are mirror images of one another ldquoOptical activityrdquo refers to the fact that the two mirror
image isomers rotate the direction of plane-polarized light in opposite directions
Enantiomers that rotate polarized light in a clockwise direction are said to be dextrorotatory (dex-tro-rota-tory) and have a + rotational value (d +) ndash In Latin dexter means ldquoright siderdquo
Enantiomers that rotate polarized light in an anti-clockwise direction are said to be laevorotatory (lay-vo-rota-tory) and have a ndash rotational value (l -) ndash In Latin laevus means ldquoleft siderdquo
There are two systems used to provide specific names to each enantiomeric form
Stereochemistry in Food Older system used for naming sugars and amino
acids Enantiomeric forms are labeled ldquoLrdquo and ldquoDrdquo
Again Laevus for left and Dexter for right Based off a compound called glyceraldehyde
chiral carbon
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Color Some of the most common natural pigment
groups are Anthocyanins
Ex Cyanidin Carotenoids
Ex Beta-carotene Chlorophyll
Ex Chlorophyll-A Heme
Ex Heme B group
heme B groupchlorophyll-A
cyanidin
β-carotene
Color Anthocyanins
Responsible for reds pinks blues in berries beets flowers (Flavonones which give color to red grapes and berries are closely related to anthocyanins)
3-ring structures with varying numbers of OH groups in varying positions
Structure and therefore color is related to pH
predominantly red at low pH (acidic) blue at high pH (basic) and colorlesspale yellow at neutral pH
Temperature May break down at high temperatures and cause browning
Exposure to metal Form complexes with iron and aluminum and can change color
Color also affected when anthocyanins bond to sugars
Color Color of anthocyanins is pH dependent (they are
acidbase indicators)
Color Carotenes
Responsible for orange yellow and red colors in foods like carrots bananas tomatoes and saffron
Characterized by long hydrocarbon chains that often have carbon rings on the ends
Have nutritional value precursors to vitamin A (important in vision) act as antioxidants
Relatively stable during food processing but presence of C=C double bonds in hydrocarbon chain opens them up to oxidative degradation as seen in fats
Causes discoloration Prevents carotenoids from being able to be converted to
vitamin A
Color
β-carotene
Color Astaxanthin is a red pigment similar to
carotenoids found in lobster crab and salmon Bonds to proteins in the live animal and gives a
bluegreen color When heated bond to protein is broken which modifies
the structure and frequency of light absorbed appears bright red
Also an antioxidant
Color Chlorophyll
Green pigment responsible for plant photosynthesis Found in green vegetables Structure is centered around a porphyrin ring ndash a
planar ring system with 4 nitrogen atoms surrounding a central metal atom (magnesium in the case of chlorophyll)
Two forms chlorophyll A and chlorophyll B In chlorophyll B an aldehyde side chain replaces a
methyl side chain When cooked plant cells release acids
Causes an H+ ion to replace magnesium atom in center of structure causing a color change to an olivebrown
Opens the possibility for photodegradation (breakdown by light)
Color
chlorophyll A
(replaced with an aldehyde in chlorophyll B)
Color Heme
Pigment found in red blood cells Structure is similar to chlorophyll but there is an iron
atom in the center of the porphyrin ring Found in the protein myoglobin responsible for
oxygen transport Bright red when bound to oxygen but slow process
of autoxidation converts iron from +2 to +3 changing color to brown (less desirable) (myoglobin metmyoglobin)
Color change can be prevented by vacuum packing or packing with an inert gas like CO2
Color
heme groupin myoglobin
Color Color in foods is a result of the structures seen in
anthocyanins carotenoids chlorophylls and hemes All of these structures include an extensive network of
delocalized pi-bonds Alternating single and double bonds is called a conjugated
system The greater the extent of pi bond delocalization the closer
together in energy bonding and antibonding orbitals become All molecules absorb light energy as it promotes e-s between
molecular orbitals (bonding and antibonding orbitals) ndash energy required is proportional to distance between orbitals (less distance = less energy)
As orbitals are close together in a conjugated system low energy light (in the visible region) is absorbed for e- promotion
Color in these groups is the product of visible light absorption - color we see is complementary to the color(s) absorbed
Molecules without an extensive delocalized pi bond network (conjugated system) lack color as orbitals are further apart and only higher energy light promotes e-s (ex the anthocyanin carbinol)
Color Some pigments are water soluble because the
structures contain a large amount of -OH groups (H-bonding) Anthocyanins
Some pigments are fat soluble (ie not water soluble) because their structures contain little or no -OH groups (no H-bonding) carotenoids
Color
Many synthetic dyes are biochemically active and could be potentially harmful
Short-term toxicity easy to test and categorize but long-term effects are more difficult to study
Use of dyes in foods must be regulated but regulations are not standardized internationally posing issues in trade
Color Cooking foods often leads to browning
Two processes responsible Maillard reactions ndash combination of sugars and
proteins Caramelization ndash dehydration of sugar
Both involve removal of water molecule(s)
Color Maillard reactions
Sugars and proteins within the food combine in a condensation reaction
Aldehyde group in sugar (O atom) combines with amino group in protein (2 H atoms)
Initial condensation products polymerize to form brown-colored melanoidins
Maillard reactions only happen gt 140deg C Rate depends on amino acid present (ex lysine
reacts faster than cysteine)
initialcondensationproduct
Color Caramelization
Happens in foods high in carbohydrates Sugars dehydrate (lose H2O) at high temperatures
leaving behind C (dark brown color)
Browning intensifies the longer food is cooked eventually burning it (pure carbon is black)
Rate depends on Sugar type (fructose in fruits caramelizes very quickly) pH ndash extremes (high and low) promote caramelization
Genetically Modified Foods
Produced when organisms with modified DNA are used in food production Used to
Provide pest or disease resistance Bt corn contains toxin from bacillis thuringiensis that kills
insect pests Fungal-resistant potatoes Nematode-resistant bananas (nematode = worm)
Improve quality and range of crop Development of higher-yielding rice varieties Development of corn that can grow in dryer environments
Produce medicines or other products in large quantities Use of chickens that have been modified to lay eggs
containing human interferon (combats tumors and viruses) Use of cows to produce milk rich in omega-3 fatty acids
(polyunsaturated fats essential to growth development brain function)
Moth larva
Genetically Modified Foods
Drawbacks Are GM foods safe Will GM food production alter the natural ecosystem Do we understand enough about genetic
modification GM foods
Can cause allergic reactions in some people Have a slightly different composition from natural foods ndash
alters diet Produce altered pollen ndash might escape and cross with natural
species Long-term effects might be catastrophic unknown so far
Texture Food texture is related to physical properties
Hardness Elasticity Viscosity
These properties can be altered by Cooking Use of dispersed systems
Dispersed system = a stabilized macroscopically homogeneous mixture of two immiscible phases
(this means two substances that would not ordinarily mix ldquoappear tordquo on a macroscopic level (although at the molecular level they are still separate)
Texture Many types of dispersed systems name depends on
the physical states of the substances mixed LiquidSolid or SolidLiquid
Solid particles suspended in a liquid is called a suspension
Ex Blood (blood cells suspended in plasma) Liquid dispersed throughout a solid medium is called a
gel Ex Fruit Jelly (water trapped in a solid protein matrix)
LiquidLiquid Stable blend of two liquids that donrsquot mix is called an
emulsion Ex Mayonaisse (oil droplets suspended in aqueous system)
LiquidGas or GasLiquid Gas bubbles trapped in liquid medium is called a foam
Ex Whipped cream or egg whites Liquid droplets suspended in gas are called aerosols
Ex Aromas from food carried through the air
Texture Dispersed systems will slowly separate over
time Separation can be slowed by adding emulsifiers
Emulsifiers are stabilizers used to keep immiscible substance together
Have surfactant capability (can bind to both substances in suspension)
Similar to micelles in the action of soaps
Ex Lecithin Found commonly in egg
yolks One end is highly charged
and water soluble (bonds toaqueous phase) the otheris not (bonds to non-aqueous phase)
Texture Lecithin in mayonnaise
Lecithin is the emulsifier Mayonnaise made by beating eggs with
vinegar and oil Lecithin is found in eggs ndash charged
hydrophilic end bonds well to vinegar uncharged hydrophobic end bonds to oil
Vigorous beating produces many small oil droplets maximizing surface area for lecithin to act on and produce a stable emulsion
Stabilizers like sodium phosphate or metals are added to prevent separation (chefs use metal bowls)
hydrophilic
hydrophobic
Stereochemistry in Food Many food-specific compounds have a chiral
carbon atom and thus exist as two different enantiomers (optical isomers) Optical isomers are mirror images of one another ldquoOptical activityrdquo refers to the fact that the two mirror
image isomers rotate the direction of plane-polarized light in opposite directions
Enantiomers that rotate polarized light in a clockwise direction are said to be dextrorotatory (dex-tro-rota-tory) and have a + rotational value (d +) ndash In Latin dexter means ldquoright siderdquo
Enantiomers that rotate polarized light in an anti-clockwise direction are said to be laevorotatory (lay-vo-rota-tory) and have a ndash rotational value (l -) ndash In Latin laevus means ldquoleft siderdquo
There are two systems used to provide specific names to each enantiomeric form
Stereochemistry in Food Older system used for naming sugars and amino
acids Enantiomeric forms are labeled ldquoLrdquo and ldquoDrdquo
Again Laevus for left and Dexter for right Based off a compound called glyceraldehyde
chiral carbon
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Color Anthocyanins
Responsible for reds pinks blues in berries beets flowers (Flavonones which give color to red grapes and berries are closely related to anthocyanins)
3-ring structures with varying numbers of OH groups in varying positions
Structure and therefore color is related to pH
predominantly red at low pH (acidic) blue at high pH (basic) and colorlesspale yellow at neutral pH
Temperature May break down at high temperatures and cause browning
Exposure to metal Form complexes with iron and aluminum and can change color
Color also affected when anthocyanins bond to sugars
Color Color of anthocyanins is pH dependent (they are
acidbase indicators)
Color Carotenes
Responsible for orange yellow and red colors in foods like carrots bananas tomatoes and saffron
Characterized by long hydrocarbon chains that often have carbon rings on the ends
Have nutritional value precursors to vitamin A (important in vision) act as antioxidants
Relatively stable during food processing but presence of C=C double bonds in hydrocarbon chain opens them up to oxidative degradation as seen in fats
Causes discoloration Prevents carotenoids from being able to be converted to
vitamin A
Color
β-carotene
Color Astaxanthin is a red pigment similar to
carotenoids found in lobster crab and salmon Bonds to proteins in the live animal and gives a
bluegreen color When heated bond to protein is broken which modifies
the structure and frequency of light absorbed appears bright red
Also an antioxidant
Color Chlorophyll
Green pigment responsible for plant photosynthesis Found in green vegetables Structure is centered around a porphyrin ring ndash a
planar ring system with 4 nitrogen atoms surrounding a central metal atom (magnesium in the case of chlorophyll)
Two forms chlorophyll A and chlorophyll B In chlorophyll B an aldehyde side chain replaces a
methyl side chain When cooked plant cells release acids
Causes an H+ ion to replace magnesium atom in center of structure causing a color change to an olivebrown
Opens the possibility for photodegradation (breakdown by light)
Color
chlorophyll A
(replaced with an aldehyde in chlorophyll B)
Color Heme
Pigment found in red blood cells Structure is similar to chlorophyll but there is an iron
atom in the center of the porphyrin ring Found in the protein myoglobin responsible for
oxygen transport Bright red when bound to oxygen but slow process
of autoxidation converts iron from +2 to +3 changing color to brown (less desirable) (myoglobin metmyoglobin)
Color change can be prevented by vacuum packing or packing with an inert gas like CO2
Color
heme groupin myoglobin
Color Color in foods is a result of the structures seen in
anthocyanins carotenoids chlorophylls and hemes All of these structures include an extensive network of
delocalized pi-bonds Alternating single and double bonds is called a conjugated
system The greater the extent of pi bond delocalization the closer
together in energy bonding and antibonding orbitals become All molecules absorb light energy as it promotes e-s between
molecular orbitals (bonding and antibonding orbitals) ndash energy required is proportional to distance between orbitals (less distance = less energy)
As orbitals are close together in a conjugated system low energy light (in the visible region) is absorbed for e- promotion
Color in these groups is the product of visible light absorption - color we see is complementary to the color(s) absorbed
Molecules without an extensive delocalized pi bond network (conjugated system) lack color as orbitals are further apart and only higher energy light promotes e-s (ex the anthocyanin carbinol)
Color Some pigments are water soluble because the
structures contain a large amount of -OH groups (H-bonding) Anthocyanins
Some pigments are fat soluble (ie not water soluble) because their structures contain little or no -OH groups (no H-bonding) carotenoids
Color
Many synthetic dyes are biochemically active and could be potentially harmful
Short-term toxicity easy to test and categorize but long-term effects are more difficult to study
Use of dyes in foods must be regulated but regulations are not standardized internationally posing issues in trade
Color Cooking foods often leads to browning
Two processes responsible Maillard reactions ndash combination of sugars and
proteins Caramelization ndash dehydration of sugar
Both involve removal of water molecule(s)
Color Maillard reactions
Sugars and proteins within the food combine in a condensation reaction
Aldehyde group in sugar (O atom) combines with amino group in protein (2 H atoms)
Initial condensation products polymerize to form brown-colored melanoidins
Maillard reactions only happen gt 140deg C Rate depends on amino acid present (ex lysine
reacts faster than cysteine)
initialcondensationproduct
Color Caramelization
Happens in foods high in carbohydrates Sugars dehydrate (lose H2O) at high temperatures
leaving behind C (dark brown color)
Browning intensifies the longer food is cooked eventually burning it (pure carbon is black)
Rate depends on Sugar type (fructose in fruits caramelizes very quickly) pH ndash extremes (high and low) promote caramelization
Genetically Modified Foods
Produced when organisms with modified DNA are used in food production Used to
Provide pest or disease resistance Bt corn contains toxin from bacillis thuringiensis that kills
insect pests Fungal-resistant potatoes Nematode-resistant bananas (nematode = worm)
Improve quality and range of crop Development of higher-yielding rice varieties Development of corn that can grow in dryer environments
Produce medicines or other products in large quantities Use of chickens that have been modified to lay eggs
containing human interferon (combats tumors and viruses) Use of cows to produce milk rich in omega-3 fatty acids
(polyunsaturated fats essential to growth development brain function)
Moth larva
Genetically Modified Foods
Drawbacks Are GM foods safe Will GM food production alter the natural ecosystem Do we understand enough about genetic
modification GM foods
Can cause allergic reactions in some people Have a slightly different composition from natural foods ndash
alters diet Produce altered pollen ndash might escape and cross with natural
species Long-term effects might be catastrophic unknown so far
Texture Food texture is related to physical properties
Hardness Elasticity Viscosity
These properties can be altered by Cooking Use of dispersed systems
Dispersed system = a stabilized macroscopically homogeneous mixture of two immiscible phases
(this means two substances that would not ordinarily mix ldquoappear tordquo on a macroscopic level (although at the molecular level they are still separate)
Texture Many types of dispersed systems name depends on
the physical states of the substances mixed LiquidSolid or SolidLiquid
Solid particles suspended in a liquid is called a suspension
Ex Blood (blood cells suspended in plasma) Liquid dispersed throughout a solid medium is called a
gel Ex Fruit Jelly (water trapped in a solid protein matrix)
LiquidLiquid Stable blend of two liquids that donrsquot mix is called an
emulsion Ex Mayonaisse (oil droplets suspended in aqueous system)
LiquidGas or GasLiquid Gas bubbles trapped in liquid medium is called a foam
Ex Whipped cream or egg whites Liquid droplets suspended in gas are called aerosols
Ex Aromas from food carried through the air
Texture Dispersed systems will slowly separate over
time Separation can be slowed by adding emulsifiers
Emulsifiers are stabilizers used to keep immiscible substance together
Have surfactant capability (can bind to both substances in suspension)
Similar to micelles in the action of soaps
Ex Lecithin Found commonly in egg
yolks One end is highly charged
and water soluble (bonds toaqueous phase) the otheris not (bonds to non-aqueous phase)
Texture Lecithin in mayonnaise
Lecithin is the emulsifier Mayonnaise made by beating eggs with
vinegar and oil Lecithin is found in eggs ndash charged
hydrophilic end bonds well to vinegar uncharged hydrophobic end bonds to oil
Vigorous beating produces many small oil droplets maximizing surface area for lecithin to act on and produce a stable emulsion
Stabilizers like sodium phosphate or metals are added to prevent separation (chefs use metal bowls)
hydrophilic
hydrophobic
Stereochemistry in Food Many food-specific compounds have a chiral
carbon atom and thus exist as two different enantiomers (optical isomers) Optical isomers are mirror images of one another ldquoOptical activityrdquo refers to the fact that the two mirror
image isomers rotate the direction of plane-polarized light in opposite directions
Enantiomers that rotate polarized light in a clockwise direction are said to be dextrorotatory (dex-tro-rota-tory) and have a + rotational value (d +) ndash In Latin dexter means ldquoright siderdquo
Enantiomers that rotate polarized light in an anti-clockwise direction are said to be laevorotatory (lay-vo-rota-tory) and have a ndash rotational value (l -) ndash In Latin laevus means ldquoleft siderdquo
There are two systems used to provide specific names to each enantiomeric form
Stereochemistry in Food Older system used for naming sugars and amino
acids Enantiomeric forms are labeled ldquoLrdquo and ldquoDrdquo
Again Laevus for left and Dexter for right Based off a compound called glyceraldehyde
chiral carbon
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Color Color of anthocyanins is pH dependent (they are
acidbase indicators)
Color Carotenes
Responsible for orange yellow and red colors in foods like carrots bananas tomatoes and saffron
Characterized by long hydrocarbon chains that often have carbon rings on the ends
Have nutritional value precursors to vitamin A (important in vision) act as antioxidants
Relatively stable during food processing but presence of C=C double bonds in hydrocarbon chain opens them up to oxidative degradation as seen in fats
Causes discoloration Prevents carotenoids from being able to be converted to
vitamin A
Color
β-carotene
Color Astaxanthin is a red pigment similar to
carotenoids found in lobster crab and salmon Bonds to proteins in the live animal and gives a
bluegreen color When heated bond to protein is broken which modifies
the structure and frequency of light absorbed appears bright red
Also an antioxidant
Color Chlorophyll
Green pigment responsible for plant photosynthesis Found in green vegetables Structure is centered around a porphyrin ring ndash a
planar ring system with 4 nitrogen atoms surrounding a central metal atom (magnesium in the case of chlorophyll)
Two forms chlorophyll A and chlorophyll B In chlorophyll B an aldehyde side chain replaces a
methyl side chain When cooked plant cells release acids
Causes an H+ ion to replace magnesium atom in center of structure causing a color change to an olivebrown
Opens the possibility for photodegradation (breakdown by light)
Color
chlorophyll A
(replaced with an aldehyde in chlorophyll B)
Color Heme
Pigment found in red blood cells Structure is similar to chlorophyll but there is an iron
atom in the center of the porphyrin ring Found in the protein myoglobin responsible for
oxygen transport Bright red when bound to oxygen but slow process
of autoxidation converts iron from +2 to +3 changing color to brown (less desirable) (myoglobin metmyoglobin)
Color change can be prevented by vacuum packing or packing with an inert gas like CO2
Color
heme groupin myoglobin
Color Color in foods is a result of the structures seen in
anthocyanins carotenoids chlorophylls and hemes All of these structures include an extensive network of
delocalized pi-bonds Alternating single and double bonds is called a conjugated
system The greater the extent of pi bond delocalization the closer
together in energy bonding and antibonding orbitals become All molecules absorb light energy as it promotes e-s between
molecular orbitals (bonding and antibonding orbitals) ndash energy required is proportional to distance between orbitals (less distance = less energy)
As orbitals are close together in a conjugated system low energy light (in the visible region) is absorbed for e- promotion
Color in these groups is the product of visible light absorption - color we see is complementary to the color(s) absorbed
Molecules without an extensive delocalized pi bond network (conjugated system) lack color as orbitals are further apart and only higher energy light promotes e-s (ex the anthocyanin carbinol)
Color Some pigments are water soluble because the
structures contain a large amount of -OH groups (H-bonding) Anthocyanins
Some pigments are fat soluble (ie not water soluble) because their structures contain little or no -OH groups (no H-bonding) carotenoids
Color
Many synthetic dyes are biochemically active and could be potentially harmful
Short-term toxicity easy to test and categorize but long-term effects are more difficult to study
Use of dyes in foods must be regulated but regulations are not standardized internationally posing issues in trade
Color Cooking foods often leads to browning
Two processes responsible Maillard reactions ndash combination of sugars and
proteins Caramelization ndash dehydration of sugar
Both involve removal of water molecule(s)
Color Maillard reactions
Sugars and proteins within the food combine in a condensation reaction
Aldehyde group in sugar (O atom) combines with amino group in protein (2 H atoms)
Initial condensation products polymerize to form brown-colored melanoidins
Maillard reactions only happen gt 140deg C Rate depends on amino acid present (ex lysine
reacts faster than cysteine)
initialcondensationproduct
Color Caramelization
Happens in foods high in carbohydrates Sugars dehydrate (lose H2O) at high temperatures
leaving behind C (dark brown color)
Browning intensifies the longer food is cooked eventually burning it (pure carbon is black)
Rate depends on Sugar type (fructose in fruits caramelizes very quickly) pH ndash extremes (high and low) promote caramelization
Genetically Modified Foods
Produced when organisms with modified DNA are used in food production Used to
Provide pest or disease resistance Bt corn contains toxin from bacillis thuringiensis that kills
insect pests Fungal-resistant potatoes Nematode-resistant bananas (nematode = worm)
Improve quality and range of crop Development of higher-yielding rice varieties Development of corn that can grow in dryer environments
Produce medicines or other products in large quantities Use of chickens that have been modified to lay eggs
containing human interferon (combats tumors and viruses) Use of cows to produce milk rich in omega-3 fatty acids
(polyunsaturated fats essential to growth development brain function)
Moth larva
Genetically Modified Foods
Drawbacks Are GM foods safe Will GM food production alter the natural ecosystem Do we understand enough about genetic
modification GM foods
Can cause allergic reactions in some people Have a slightly different composition from natural foods ndash
alters diet Produce altered pollen ndash might escape and cross with natural
species Long-term effects might be catastrophic unknown so far
Texture Food texture is related to physical properties
Hardness Elasticity Viscosity
These properties can be altered by Cooking Use of dispersed systems
Dispersed system = a stabilized macroscopically homogeneous mixture of two immiscible phases
(this means two substances that would not ordinarily mix ldquoappear tordquo on a macroscopic level (although at the molecular level they are still separate)
Texture Many types of dispersed systems name depends on
the physical states of the substances mixed LiquidSolid or SolidLiquid
Solid particles suspended in a liquid is called a suspension
Ex Blood (blood cells suspended in plasma) Liquid dispersed throughout a solid medium is called a
gel Ex Fruit Jelly (water trapped in a solid protein matrix)
LiquidLiquid Stable blend of two liquids that donrsquot mix is called an
emulsion Ex Mayonaisse (oil droplets suspended in aqueous system)
LiquidGas or GasLiquid Gas bubbles trapped in liquid medium is called a foam
Ex Whipped cream or egg whites Liquid droplets suspended in gas are called aerosols
Ex Aromas from food carried through the air
Texture Dispersed systems will slowly separate over
time Separation can be slowed by adding emulsifiers
Emulsifiers are stabilizers used to keep immiscible substance together
Have surfactant capability (can bind to both substances in suspension)
Similar to micelles in the action of soaps
Ex Lecithin Found commonly in egg
yolks One end is highly charged
and water soluble (bonds toaqueous phase) the otheris not (bonds to non-aqueous phase)
Texture Lecithin in mayonnaise
Lecithin is the emulsifier Mayonnaise made by beating eggs with
vinegar and oil Lecithin is found in eggs ndash charged
hydrophilic end bonds well to vinegar uncharged hydrophobic end bonds to oil
Vigorous beating produces many small oil droplets maximizing surface area for lecithin to act on and produce a stable emulsion
Stabilizers like sodium phosphate or metals are added to prevent separation (chefs use metal bowls)
hydrophilic
hydrophobic
Stereochemistry in Food Many food-specific compounds have a chiral
carbon atom and thus exist as two different enantiomers (optical isomers) Optical isomers are mirror images of one another ldquoOptical activityrdquo refers to the fact that the two mirror
image isomers rotate the direction of plane-polarized light in opposite directions
Enantiomers that rotate polarized light in a clockwise direction are said to be dextrorotatory (dex-tro-rota-tory) and have a + rotational value (d +) ndash In Latin dexter means ldquoright siderdquo
Enantiomers that rotate polarized light in an anti-clockwise direction are said to be laevorotatory (lay-vo-rota-tory) and have a ndash rotational value (l -) ndash In Latin laevus means ldquoleft siderdquo
There are two systems used to provide specific names to each enantiomeric form
Stereochemistry in Food Older system used for naming sugars and amino
acids Enantiomeric forms are labeled ldquoLrdquo and ldquoDrdquo
Again Laevus for left and Dexter for right Based off a compound called glyceraldehyde
chiral carbon
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Color Carotenes
Responsible for orange yellow and red colors in foods like carrots bananas tomatoes and saffron
Characterized by long hydrocarbon chains that often have carbon rings on the ends
Have nutritional value precursors to vitamin A (important in vision) act as antioxidants
Relatively stable during food processing but presence of C=C double bonds in hydrocarbon chain opens them up to oxidative degradation as seen in fats
Causes discoloration Prevents carotenoids from being able to be converted to
vitamin A
Color
β-carotene
Color Astaxanthin is a red pigment similar to
carotenoids found in lobster crab and salmon Bonds to proteins in the live animal and gives a
bluegreen color When heated bond to protein is broken which modifies
the structure and frequency of light absorbed appears bright red
Also an antioxidant
Color Chlorophyll
Green pigment responsible for plant photosynthesis Found in green vegetables Structure is centered around a porphyrin ring ndash a
planar ring system with 4 nitrogen atoms surrounding a central metal atom (magnesium in the case of chlorophyll)
Two forms chlorophyll A and chlorophyll B In chlorophyll B an aldehyde side chain replaces a
methyl side chain When cooked plant cells release acids
Causes an H+ ion to replace magnesium atom in center of structure causing a color change to an olivebrown
Opens the possibility for photodegradation (breakdown by light)
Color
chlorophyll A
(replaced with an aldehyde in chlorophyll B)
Color Heme
Pigment found in red blood cells Structure is similar to chlorophyll but there is an iron
atom in the center of the porphyrin ring Found in the protein myoglobin responsible for
oxygen transport Bright red when bound to oxygen but slow process
of autoxidation converts iron from +2 to +3 changing color to brown (less desirable) (myoglobin metmyoglobin)
Color change can be prevented by vacuum packing or packing with an inert gas like CO2
Color
heme groupin myoglobin
Color Color in foods is a result of the structures seen in
anthocyanins carotenoids chlorophylls and hemes All of these structures include an extensive network of
delocalized pi-bonds Alternating single and double bonds is called a conjugated
system The greater the extent of pi bond delocalization the closer
together in energy bonding and antibonding orbitals become All molecules absorb light energy as it promotes e-s between
molecular orbitals (bonding and antibonding orbitals) ndash energy required is proportional to distance between orbitals (less distance = less energy)
As orbitals are close together in a conjugated system low energy light (in the visible region) is absorbed for e- promotion
Color in these groups is the product of visible light absorption - color we see is complementary to the color(s) absorbed
Molecules without an extensive delocalized pi bond network (conjugated system) lack color as orbitals are further apart and only higher energy light promotes e-s (ex the anthocyanin carbinol)
Color Some pigments are water soluble because the
structures contain a large amount of -OH groups (H-bonding) Anthocyanins
Some pigments are fat soluble (ie not water soluble) because their structures contain little or no -OH groups (no H-bonding) carotenoids
Color
Many synthetic dyes are biochemically active and could be potentially harmful
Short-term toxicity easy to test and categorize but long-term effects are more difficult to study
Use of dyes in foods must be regulated but regulations are not standardized internationally posing issues in trade
Color Cooking foods often leads to browning
Two processes responsible Maillard reactions ndash combination of sugars and
proteins Caramelization ndash dehydration of sugar
Both involve removal of water molecule(s)
Color Maillard reactions
Sugars and proteins within the food combine in a condensation reaction
Aldehyde group in sugar (O atom) combines with amino group in protein (2 H atoms)
Initial condensation products polymerize to form brown-colored melanoidins
Maillard reactions only happen gt 140deg C Rate depends on amino acid present (ex lysine
reacts faster than cysteine)
initialcondensationproduct
Color Caramelization
Happens in foods high in carbohydrates Sugars dehydrate (lose H2O) at high temperatures
leaving behind C (dark brown color)
Browning intensifies the longer food is cooked eventually burning it (pure carbon is black)
Rate depends on Sugar type (fructose in fruits caramelizes very quickly) pH ndash extremes (high and low) promote caramelization
Genetically Modified Foods
Produced when organisms with modified DNA are used in food production Used to
Provide pest or disease resistance Bt corn contains toxin from bacillis thuringiensis that kills
insect pests Fungal-resistant potatoes Nematode-resistant bananas (nematode = worm)
Improve quality and range of crop Development of higher-yielding rice varieties Development of corn that can grow in dryer environments
Produce medicines or other products in large quantities Use of chickens that have been modified to lay eggs
containing human interferon (combats tumors and viruses) Use of cows to produce milk rich in omega-3 fatty acids
(polyunsaturated fats essential to growth development brain function)
Moth larva
Genetically Modified Foods
Drawbacks Are GM foods safe Will GM food production alter the natural ecosystem Do we understand enough about genetic
modification GM foods
Can cause allergic reactions in some people Have a slightly different composition from natural foods ndash
alters diet Produce altered pollen ndash might escape and cross with natural
species Long-term effects might be catastrophic unknown so far
Texture Food texture is related to physical properties
Hardness Elasticity Viscosity
These properties can be altered by Cooking Use of dispersed systems
Dispersed system = a stabilized macroscopically homogeneous mixture of two immiscible phases
(this means two substances that would not ordinarily mix ldquoappear tordquo on a macroscopic level (although at the molecular level they are still separate)
Texture Many types of dispersed systems name depends on
the physical states of the substances mixed LiquidSolid or SolidLiquid
Solid particles suspended in a liquid is called a suspension
Ex Blood (blood cells suspended in plasma) Liquid dispersed throughout a solid medium is called a
gel Ex Fruit Jelly (water trapped in a solid protein matrix)
LiquidLiquid Stable blend of two liquids that donrsquot mix is called an
emulsion Ex Mayonaisse (oil droplets suspended in aqueous system)
LiquidGas or GasLiquid Gas bubbles trapped in liquid medium is called a foam
Ex Whipped cream or egg whites Liquid droplets suspended in gas are called aerosols
Ex Aromas from food carried through the air
Texture Dispersed systems will slowly separate over
time Separation can be slowed by adding emulsifiers
Emulsifiers are stabilizers used to keep immiscible substance together
Have surfactant capability (can bind to both substances in suspension)
Similar to micelles in the action of soaps
Ex Lecithin Found commonly in egg
yolks One end is highly charged
and water soluble (bonds toaqueous phase) the otheris not (bonds to non-aqueous phase)
Texture Lecithin in mayonnaise
Lecithin is the emulsifier Mayonnaise made by beating eggs with
vinegar and oil Lecithin is found in eggs ndash charged
hydrophilic end bonds well to vinegar uncharged hydrophobic end bonds to oil
Vigorous beating produces many small oil droplets maximizing surface area for lecithin to act on and produce a stable emulsion
Stabilizers like sodium phosphate or metals are added to prevent separation (chefs use metal bowls)
hydrophilic
hydrophobic
Stereochemistry in Food Many food-specific compounds have a chiral
carbon atom and thus exist as two different enantiomers (optical isomers) Optical isomers are mirror images of one another ldquoOptical activityrdquo refers to the fact that the two mirror
image isomers rotate the direction of plane-polarized light in opposite directions
Enantiomers that rotate polarized light in a clockwise direction are said to be dextrorotatory (dex-tro-rota-tory) and have a + rotational value (d +) ndash In Latin dexter means ldquoright siderdquo
Enantiomers that rotate polarized light in an anti-clockwise direction are said to be laevorotatory (lay-vo-rota-tory) and have a ndash rotational value (l -) ndash In Latin laevus means ldquoleft siderdquo
There are two systems used to provide specific names to each enantiomeric form
Stereochemistry in Food Older system used for naming sugars and amino
acids Enantiomeric forms are labeled ldquoLrdquo and ldquoDrdquo
Again Laevus for left and Dexter for right Based off a compound called glyceraldehyde
chiral carbon
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Color
β-carotene
Color Astaxanthin is a red pigment similar to
carotenoids found in lobster crab and salmon Bonds to proteins in the live animal and gives a
bluegreen color When heated bond to protein is broken which modifies
the structure and frequency of light absorbed appears bright red
Also an antioxidant
Color Chlorophyll
Green pigment responsible for plant photosynthesis Found in green vegetables Structure is centered around a porphyrin ring ndash a
planar ring system with 4 nitrogen atoms surrounding a central metal atom (magnesium in the case of chlorophyll)
Two forms chlorophyll A and chlorophyll B In chlorophyll B an aldehyde side chain replaces a
methyl side chain When cooked plant cells release acids
Causes an H+ ion to replace magnesium atom in center of structure causing a color change to an olivebrown
Opens the possibility for photodegradation (breakdown by light)
Color
chlorophyll A
(replaced with an aldehyde in chlorophyll B)
Color Heme
Pigment found in red blood cells Structure is similar to chlorophyll but there is an iron
atom in the center of the porphyrin ring Found in the protein myoglobin responsible for
oxygen transport Bright red when bound to oxygen but slow process
of autoxidation converts iron from +2 to +3 changing color to brown (less desirable) (myoglobin metmyoglobin)
Color change can be prevented by vacuum packing or packing with an inert gas like CO2
Color
heme groupin myoglobin
Color Color in foods is a result of the structures seen in
anthocyanins carotenoids chlorophylls and hemes All of these structures include an extensive network of
delocalized pi-bonds Alternating single and double bonds is called a conjugated
system The greater the extent of pi bond delocalization the closer
together in energy bonding and antibonding orbitals become All molecules absorb light energy as it promotes e-s between
molecular orbitals (bonding and antibonding orbitals) ndash energy required is proportional to distance between orbitals (less distance = less energy)
As orbitals are close together in a conjugated system low energy light (in the visible region) is absorbed for e- promotion
Color in these groups is the product of visible light absorption - color we see is complementary to the color(s) absorbed
Molecules without an extensive delocalized pi bond network (conjugated system) lack color as orbitals are further apart and only higher energy light promotes e-s (ex the anthocyanin carbinol)
Color Some pigments are water soluble because the
structures contain a large amount of -OH groups (H-bonding) Anthocyanins
Some pigments are fat soluble (ie not water soluble) because their structures contain little or no -OH groups (no H-bonding) carotenoids
Color
Many synthetic dyes are biochemically active and could be potentially harmful
Short-term toxicity easy to test and categorize but long-term effects are more difficult to study
Use of dyes in foods must be regulated but regulations are not standardized internationally posing issues in trade
Color Cooking foods often leads to browning
Two processes responsible Maillard reactions ndash combination of sugars and
proteins Caramelization ndash dehydration of sugar
Both involve removal of water molecule(s)
Color Maillard reactions
Sugars and proteins within the food combine in a condensation reaction
Aldehyde group in sugar (O atom) combines with amino group in protein (2 H atoms)
Initial condensation products polymerize to form brown-colored melanoidins
Maillard reactions only happen gt 140deg C Rate depends on amino acid present (ex lysine
reacts faster than cysteine)
initialcondensationproduct
Color Caramelization
Happens in foods high in carbohydrates Sugars dehydrate (lose H2O) at high temperatures
leaving behind C (dark brown color)
Browning intensifies the longer food is cooked eventually burning it (pure carbon is black)
Rate depends on Sugar type (fructose in fruits caramelizes very quickly) pH ndash extremes (high and low) promote caramelization
Genetically Modified Foods
Produced when organisms with modified DNA are used in food production Used to
Provide pest or disease resistance Bt corn contains toxin from bacillis thuringiensis that kills
insect pests Fungal-resistant potatoes Nematode-resistant bananas (nematode = worm)
Improve quality and range of crop Development of higher-yielding rice varieties Development of corn that can grow in dryer environments
Produce medicines or other products in large quantities Use of chickens that have been modified to lay eggs
containing human interferon (combats tumors and viruses) Use of cows to produce milk rich in omega-3 fatty acids
(polyunsaturated fats essential to growth development brain function)
Moth larva
Genetically Modified Foods
Drawbacks Are GM foods safe Will GM food production alter the natural ecosystem Do we understand enough about genetic
modification GM foods
Can cause allergic reactions in some people Have a slightly different composition from natural foods ndash
alters diet Produce altered pollen ndash might escape and cross with natural
species Long-term effects might be catastrophic unknown so far
Texture Food texture is related to physical properties
Hardness Elasticity Viscosity
These properties can be altered by Cooking Use of dispersed systems
Dispersed system = a stabilized macroscopically homogeneous mixture of two immiscible phases
(this means two substances that would not ordinarily mix ldquoappear tordquo on a macroscopic level (although at the molecular level they are still separate)
Texture Many types of dispersed systems name depends on
the physical states of the substances mixed LiquidSolid or SolidLiquid
Solid particles suspended in a liquid is called a suspension
Ex Blood (blood cells suspended in plasma) Liquid dispersed throughout a solid medium is called a
gel Ex Fruit Jelly (water trapped in a solid protein matrix)
LiquidLiquid Stable blend of two liquids that donrsquot mix is called an
emulsion Ex Mayonaisse (oil droplets suspended in aqueous system)
LiquidGas or GasLiquid Gas bubbles trapped in liquid medium is called a foam
Ex Whipped cream or egg whites Liquid droplets suspended in gas are called aerosols
Ex Aromas from food carried through the air
Texture Dispersed systems will slowly separate over
time Separation can be slowed by adding emulsifiers
Emulsifiers are stabilizers used to keep immiscible substance together
Have surfactant capability (can bind to both substances in suspension)
Similar to micelles in the action of soaps
Ex Lecithin Found commonly in egg
yolks One end is highly charged
and water soluble (bonds toaqueous phase) the otheris not (bonds to non-aqueous phase)
Texture Lecithin in mayonnaise
Lecithin is the emulsifier Mayonnaise made by beating eggs with
vinegar and oil Lecithin is found in eggs ndash charged
hydrophilic end bonds well to vinegar uncharged hydrophobic end bonds to oil
Vigorous beating produces many small oil droplets maximizing surface area for lecithin to act on and produce a stable emulsion
Stabilizers like sodium phosphate or metals are added to prevent separation (chefs use metal bowls)
hydrophilic
hydrophobic
Stereochemistry in Food Many food-specific compounds have a chiral
carbon atom and thus exist as two different enantiomers (optical isomers) Optical isomers are mirror images of one another ldquoOptical activityrdquo refers to the fact that the two mirror
image isomers rotate the direction of plane-polarized light in opposite directions
Enantiomers that rotate polarized light in a clockwise direction are said to be dextrorotatory (dex-tro-rota-tory) and have a + rotational value (d +) ndash In Latin dexter means ldquoright siderdquo
Enantiomers that rotate polarized light in an anti-clockwise direction are said to be laevorotatory (lay-vo-rota-tory) and have a ndash rotational value (l -) ndash In Latin laevus means ldquoleft siderdquo
There are two systems used to provide specific names to each enantiomeric form
Stereochemistry in Food Older system used for naming sugars and amino
acids Enantiomeric forms are labeled ldquoLrdquo and ldquoDrdquo
Again Laevus for left and Dexter for right Based off a compound called glyceraldehyde
chiral carbon
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Color Astaxanthin is a red pigment similar to
carotenoids found in lobster crab and salmon Bonds to proteins in the live animal and gives a
bluegreen color When heated bond to protein is broken which modifies
the structure and frequency of light absorbed appears bright red
Also an antioxidant
Color Chlorophyll
Green pigment responsible for plant photosynthesis Found in green vegetables Structure is centered around a porphyrin ring ndash a
planar ring system with 4 nitrogen atoms surrounding a central metal atom (magnesium in the case of chlorophyll)
Two forms chlorophyll A and chlorophyll B In chlorophyll B an aldehyde side chain replaces a
methyl side chain When cooked plant cells release acids
Causes an H+ ion to replace magnesium atom in center of structure causing a color change to an olivebrown
Opens the possibility for photodegradation (breakdown by light)
Color
chlorophyll A
(replaced with an aldehyde in chlorophyll B)
Color Heme
Pigment found in red blood cells Structure is similar to chlorophyll but there is an iron
atom in the center of the porphyrin ring Found in the protein myoglobin responsible for
oxygen transport Bright red when bound to oxygen but slow process
of autoxidation converts iron from +2 to +3 changing color to brown (less desirable) (myoglobin metmyoglobin)
Color change can be prevented by vacuum packing or packing with an inert gas like CO2
Color
heme groupin myoglobin
Color Color in foods is a result of the structures seen in
anthocyanins carotenoids chlorophylls and hemes All of these structures include an extensive network of
delocalized pi-bonds Alternating single and double bonds is called a conjugated
system The greater the extent of pi bond delocalization the closer
together in energy bonding and antibonding orbitals become All molecules absorb light energy as it promotes e-s between
molecular orbitals (bonding and antibonding orbitals) ndash energy required is proportional to distance between orbitals (less distance = less energy)
As orbitals are close together in a conjugated system low energy light (in the visible region) is absorbed for e- promotion
Color in these groups is the product of visible light absorption - color we see is complementary to the color(s) absorbed
Molecules without an extensive delocalized pi bond network (conjugated system) lack color as orbitals are further apart and only higher energy light promotes e-s (ex the anthocyanin carbinol)
Color Some pigments are water soluble because the
structures contain a large amount of -OH groups (H-bonding) Anthocyanins
Some pigments are fat soluble (ie not water soluble) because their structures contain little or no -OH groups (no H-bonding) carotenoids
Color
Many synthetic dyes are biochemically active and could be potentially harmful
Short-term toxicity easy to test and categorize but long-term effects are more difficult to study
Use of dyes in foods must be regulated but regulations are not standardized internationally posing issues in trade
Color Cooking foods often leads to browning
Two processes responsible Maillard reactions ndash combination of sugars and
proteins Caramelization ndash dehydration of sugar
Both involve removal of water molecule(s)
Color Maillard reactions
Sugars and proteins within the food combine in a condensation reaction
Aldehyde group in sugar (O atom) combines with amino group in protein (2 H atoms)
Initial condensation products polymerize to form brown-colored melanoidins
Maillard reactions only happen gt 140deg C Rate depends on amino acid present (ex lysine
reacts faster than cysteine)
initialcondensationproduct
Color Caramelization
Happens in foods high in carbohydrates Sugars dehydrate (lose H2O) at high temperatures
leaving behind C (dark brown color)
Browning intensifies the longer food is cooked eventually burning it (pure carbon is black)
Rate depends on Sugar type (fructose in fruits caramelizes very quickly) pH ndash extremes (high and low) promote caramelization
Genetically Modified Foods
Produced when organisms with modified DNA are used in food production Used to
Provide pest or disease resistance Bt corn contains toxin from bacillis thuringiensis that kills
insect pests Fungal-resistant potatoes Nematode-resistant bananas (nematode = worm)
Improve quality and range of crop Development of higher-yielding rice varieties Development of corn that can grow in dryer environments
Produce medicines or other products in large quantities Use of chickens that have been modified to lay eggs
containing human interferon (combats tumors and viruses) Use of cows to produce milk rich in omega-3 fatty acids
(polyunsaturated fats essential to growth development brain function)
Moth larva
Genetically Modified Foods
Drawbacks Are GM foods safe Will GM food production alter the natural ecosystem Do we understand enough about genetic
modification GM foods
Can cause allergic reactions in some people Have a slightly different composition from natural foods ndash
alters diet Produce altered pollen ndash might escape and cross with natural
species Long-term effects might be catastrophic unknown so far
Texture Food texture is related to physical properties
Hardness Elasticity Viscosity
These properties can be altered by Cooking Use of dispersed systems
Dispersed system = a stabilized macroscopically homogeneous mixture of two immiscible phases
(this means two substances that would not ordinarily mix ldquoappear tordquo on a macroscopic level (although at the molecular level they are still separate)
Texture Many types of dispersed systems name depends on
the physical states of the substances mixed LiquidSolid or SolidLiquid
Solid particles suspended in a liquid is called a suspension
Ex Blood (blood cells suspended in plasma) Liquid dispersed throughout a solid medium is called a
gel Ex Fruit Jelly (water trapped in a solid protein matrix)
LiquidLiquid Stable blend of two liquids that donrsquot mix is called an
emulsion Ex Mayonaisse (oil droplets suspended in aqueous system)
LiquidGas or GasLiquid Gas bubbles trapped in liquid medium is called a foam
Ex Whipped cream or egg whites Liquid droplets suspended in gas are called aerosols
Ex Aromas from food carried through the air
Texture Dispersed systems will slowly separate over
time Separation can be slowed by adding emulsifiers
Emulsifiers are stabilizers used to keep immiscible substance together
Have surfactant capability (can bind to both substances in suspension)
Similar to micelles in the action of soaps
Ex Lecithin Found commonly in egg
yolks One end is highly charged
and water soluble (bonds toaqueous phase) the otheris not (bonds to non-aqueous phase)
Texture Lecithin in mayonnaise
Lecithin is the emulsifier Mayonnaise made by beating eggs with
vinegar and oil Lecithin is found in eggs ndash charged
hydrophilic end bonds well to vinegar uncharged hydrophobic end bonds to oil
Vigorous beating produces many small oil droplets maximizing surface area for lecithin to act on and produce a stable emulsion
Stabilizers like sodium phosphate or metals are added to prevent separation (chefs use metal bowls)
hydrophilic
hydrophobic
Stereochemistry in Food Many food-specific compounds have a chiral
carbon atom and thus exist as two different enantiomers (optical isomers) Optical isomers are mirror images of one another ldquoOptical activityrdquo refers to the fact that the two mirror
image isomers rotate the direction of plane-polarized light in opposite directions
Enantiomers that rotate polarized light in a clockwise direction are said to be dextrorotatory (dex-tro-rota-tory) and have a + rotational value (d +) ndash In Latin dexter means ldquoright siderdquo
Enantiomers that rotate polarized light in an anti-clockwise direction are said to be laevorotatory (lay-vo-rota-tory) and have a ndash rotational value (l -) ndash In Latin laevus means ldquoleft siderdquo
There are two systems used to provide specific names to each enantiomeric form
Stereochemistry in Food Older system used for naming sugars and amino
acids Enantiomeric forms are labeled ldquoLrdquo and ldquoDrdquo
Again Laevus for left and Dexter for right Based off a compound called glyceraldehyde
chiral carbon
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Color Chlorophyll
Green pigment responsible for plant photosynthesis Found in green vegetables Structure is centered around a porphyrin ring ndash a
planar ring system with 4 nitrogen atoms surrounding a central metal atom (magnesium in the case of chlorophyll)
Two forms chlorophyll A and chlorophyll B In chlorophyll B an aldehyde side chain replaces a
methyl side chain When cooked plant cells release acids
Causes an H+ ion to replace magnesium atom in center of structure causing a color change to an olivebrown
Opens the possibility for photodegradation (breakdown by light)
Color
chlorophyll A
(replaced with an aldehyde in chlorophyll B)
Color Heme
Pigment found in red blood cells Structure is similar to chlorophyll but there is an iron
atom in the center of the porphyrin ring Found in the protein myoglobin responsible for
oxygen transport Bright red when bound to oxygen but slow process
of autoxidation converts iron from +2 to +3 changing color to brown (less desirable) (myoglobin metmyoglobin)
Color change can be prevented by vacuum packing or packing with an inert gas like CO2
Color
heme groupin myoglobin
Color Color in foods is a result of the structures seen in
anthocyanins carotenoids chlorophylls and hemes All of these structures include an extensive network of
delocalized pi-bonds Alternating single and double bonds is called a conjugated
system The greater the extent of pi bond delocalization the closer
together in energy bonding and antibonding orbitals become All molecules absorb light energy as it promotes e-s between
molecular orbitals (bonding and antibonding orbitals) ndash energy required is proportional to distance between orbitals (less distance = less energy)
As orbitals are close together in a conjugated system low energy light (in the visible region) is absorbed for e- promotion
Color in these groups is the product of visible light absorption - color we see is complementary to the color(s) absorbed
Molecules without an extensive delocalized pi bond network (conjugated system) lack color as orbitals are further apart and only higher energy light promotes e-s (ex the anthocyanin carbinol)
Color Some pigments are water soluble because the
structures contain a large amount of -OH groups (H-bonding) Anthocyanins
Some pigments are fat soluble (ie not water soluble) because their structures contain little or no -OH groups (no H-bonding) carotenoids
Color
Many synthetic dyes are biochemically active and could be potentially harmful
Short-term toxicity easy to test and categorize but long-term effects are more difficult to study
Use of dyes in foods must be regulated but regulations are not standardized internationally posing issues in trade
Color Cooking foods often leads to browning
Two processes responsible Maillard reactions ndash combination of sugars and
proteins Caramelization ndash dehydration of sugar
Both involve removal of water molecule(s)
Color Maillard reactions
Sugars and proteins within the food combine in a condensation reaction
Aldehyde group in sugar (O atom) combines with amino group in protein (2 H atoms)
Initial condensation products polymerize to form brown-colored melanoidins
Maillard reactions only happen gt 140deg C Rate depends on amino acid present (ex lysine
reacts faster than cysteine)
initialcondensationproduct
Color Caramelization
Happens in foods high in carbohydrates Sugars dehydrate (lose H2O) at high temperatures
leaving behind C (dark brown color)
Browning intensifies the longer food is cooked eventually burning it (pure carbon is black)
Rate depends on Sugar type (fructose in fruits caramelizes very quickly) pH ndash extremes (high and low) promote caramelization
Genetically Modified Foods
Produced when organisms with modified DNA are used in food production Used to
Provide pest or disease resistance Bt corn contains toxin from bacillis thuringiensis that kills
insect pests Fungal-resistant potatoes Nematode-resistant bananas (nematode = worm)
Improve quality and range of crop Development of higher-yielding rice varieties Development of corn that can grow in dryer environments
Produce medicines or other products in large quantities Use of chickens that have been modified to lay eggs
containing human interferon (combats tumors and viruses) Use of cows to produce milk rich in omega-3 fatty acids
(polyunsaturated fats essential to growth development brain function)
Moth larva
Genetically Modified Foods
Drawbacks Are GM foods safe Will GM food production alter the natural ecosystem Do we understand enough about genetic
modification GM foods
Can cause allergic reactions in some people Have a slightly different composition from natural foods ndash
alters diet Produce altered pollen ndash might escape and cross with natural
species Long-term effects might be catastrophic unknown so far
Texture Food texture is related to physical properties
Hardness Elasticity Viscosity
These properties can be altered by Cooking Use of dispersed systems
Dispersed system = a stabilized macroscopically homogeneous mixture of two immiscible phases
(this means two substances that would not ordinarily mix ldquoappear tordquo on a macroscopic level (although at the molecular level they are still separate)
Texture Many types of dispersed systems name depends on
the physical states of the substances mixed LiquidSolid or SolidLiquid
Solid particles suspended in a liquid is called a suspension
Ex Blood (blood cells suspended in plasma) Liquid dispersed throughout a solid medium is called a
gel Ex Fruit Jelly (water trapped in a solid protein matrix)
LiquidLiquid Stable blend of two liquids that donrsquot mix is called an
emulsion Ex Mayonaisse (oil droplets suspended in aqueous system)
LiquidGas or GasLiquid Gas bubbles trapped in liquid medium is called a foam
Ex Whipped cream or egg whites Liquid droplets suspended in gas are called aerosols
Ex Aromas from food carried through the air
Texture Dispersed systems will slowly separate over
time Separation can be slowed by adding emulsifiers
Emulsifiers are stabilizers used to keep immiscible substance together
Have surfactant capability (can bind to both substances in suspension)
Similar to micelles in the action of soaps
Ex Lecithin Found commonly in egg
yolks One end is highly charged
and water soluble (bonds toaqueous phase) the otheris not (bonds to non-aqueous phase)
Texture Lecithin in mayonnaise
Lecithin is the emulsifier Mayonnaise made by beating eggs with
vinegar and oil Lecithin is found in eggs ndash charged
hydrophilic end bonds well to vinegar uncharged hydrophobic end bonds to oil
Vigorous beating produces many small oil droplets maximizing surface area for lecithin to act on and produce a stable emulsion
Stabilizers like sodium phosphate or metals are added to prevent separation (chefs use metal bowls)
hydrophilic
hydrophobic
Stereochemistry in Food Many food-specific compounds have a chiral
carbon atom and thus exist as two different enantiomers (optical isomers) Optical isomers are mirror images of one another ldquoOptical activityrdquo refers to the fact that the two mirror
image isomers rotate the direction of plane-polarized light in opposite directions
Enantiomers that rotate polarized light in a clockwise direction are said to be dextrorotatory (dex-tro-rota-tory) and have a + rotational value (d +) ndash In Latin dexter means ldquoright siderdquo
Enantiomers that rotate polarized light in an anti-clockwise direction are said to be laevorotatory (lay-vo-rota-tory) and have a ndash rotational value (l -) ndash In Latin laevus means ldquoleft siderdquo
There are two systems used to provide specific names to each enantiomeric form
Stereochemistry in Food Older system used for naming sugars and amino
acids Enantiomeric forms are labeled ldquoLrdquo and ldquoDrdquo
Again Laevus for left and Dexter for right Based off a compound called glyceraldehyde
chiral carbon
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Color
chlorophyll A
(replaced with an aldehyde in chlorophyll B)
Color Heme
Pigment found in red blood cells Structure is similar to chlorophyll but there is an iron
atom in the center of the porphyrin ring Found in the protein myoglobin responsible for
oxygen transport Bright red when bound to oxygen but slow process
of autoxidation converts iron from +2 to +3 changing color to brown (less desirable) (myoglobin metmyoglobin)
Color change can be prevented by vacuum packing or packing with an inert gas like CO2
Color
heme groupin myoglobin
Color Color in foods is a result of the structures seen in
anthocyanins carotenoids chlorophylls and hemes All of these structures include an extensive network of
delocalized pi-bonds Alternating single and double bonds is called a conjugated
system The greater the extent of pi bond delocalization the closer
together in energy bonding and antibonding orbitals become All molecules absorb light energy as it promotes e-s between
molecular orbitals (bonding and antibonding orbitals) ndash energy required is proportional to distance between orbitals (less distance = less energy)
As orbitals are close together in a conjugated system low energy light (in the visible region) is absorbed for e- promotion
Color in these groups is the product of visible light absorption - color we see is complementary to the color(s) absorbed
Molecules without an extensive delocalized pi bond network (conjugated system) lack color as orbitals are further apart and only higher energy light promotes e-s (ex the anthocyanin carbinol)
Color Some pigments are water soluble because the
structures contain a large amount of -OH groups (H-bonding) Anthocyanins
Some pigments are fat soluble (ie not water soluble) because their structures contain little or no -OH groups (no H-bonding) carotenoids
Color
Many synthetic dyes are biochemically active and could be potentially harmful
Short-term toxicity easy to test and categorize but long-term effects are more difficult to study
Use of dyes in foods must be regulated but regulations are not standardized internationally posing issues in trade
Color Cooking foods often leads to browning
Two processes responsible Maillard reactions ndash combination of sugars and
proteins Caramelization ndash dehydration of sugar
Both involve removal of water molecule(s)
Color Maillard reactions
Sugars and proteins within the food combine in a condensation reaction
Aldehyde group in sugar (O atom) combines with amino group in protein (2 H atoms)
Initial condensation products polymerize to form brown-colored melanoidins
Maillard reactions only happen gt 140deg C Rate depends on amino acid present (ex lysine
reacts faster than cysteine)
initialcondensationproduct
Color Caramelization
Happens in foods high in carbohydrates Sugars dehydrate (lose H2O) at high temperatures
leaving behind C (dark brown color)
Browning intensifies the longer food is cooked eventually burning it (pure carbon is black)
Rate depends on Sugar type (fructose in fruits caramelizes very quickly) pH ndash extremes (high and low) promote caramelization
Genetically Modified Foods
Produced when organisms with modified DNA are used in food production Used to
Provide pest or disease resistance Bt corn contains toxin from bacillis thuringiensis that kills
insect pests Fungal-resistant potatoes Nematode-resistant bananas (nematode = worm)
Improve quality and range of crop Development of higher-yielding rice varieties Development of corn that can grow in dryer environments
Produce medicines or other products in large quantities Use of chickens that have been modified to lay eggs
containing human interferon (combats tumors and viruses) Use of cows to produce milk rich in omega-3 fatty acids
(polyunsaturated fats essential to growth development brain function)
Moth larva
Genetically Modified Foods
Drawbacks Are GM foods safe Will GM food production alter the natural ecosystem Do we understand enough about genetic
modification GM foods
Can cause allergic reactions in some people Have a slightly different composition from natural foods ndash
alters diet Produce altered pollen ndash might escape and cross with natural
species Long-term effects might be catastrophic unknown so far
Texture Food texture is related to physical properties
Hardness Elasticity Viscosity
These properties can be altered by Cooking Use of dispersed systems
Dispersed system = a stabilized macroscopically homogeneous mixture of two immiscible phases
(this means two substances that would not ordinarily mix ldquoappear tordquo on a macroscopic level (although at the molecular level they are still separate)
Texture Many types of dispersed systems name depends on
the physical states of the substances mixed LiquidSolid or SolidLiquid
Solid particles suspended in a liquid is called a suspension
Ex Blood (blood cells suspended in plasma) Liquid dispersed throughout a solid medium is called a
gel Ex Fruit Jelly (water trapped in a solid protein matrix)
LiquidLiquid Stable blend of two liquids that donrsquot mix is called an
emulsion Ex Mayonaisse (oil droplets suspended in aqueous system)
LiquidGas or GasLiquid Gas bubbles trapped in liquid medium is called a foam
Ex Whipped cream or egg whites Liquid droplets suspended in gas are called aerosols
Ex Aromas from food carried through the air
Texture Dispersed systems will slowly separate over
time Separation can be slowed by adding emulsifiers
Emulsifiers are stabilizers used to keep immiscible substance together
Have surfactant capability (can bind to both substances in suspension)
Similar to micelles in the action of soaps
Ex Lecithin Found commonly in egg
yolks One end is highly charged
and water soluble (bonds toaqueous phase) the otheris not (bonds to non-aqueous phase)
Texture Lecithin in mayonnaise
Lecithin is the emulsifier Mayonnaise made by beating eggs with
vinegar and oil Lecithin is found in eggs ndash charged
hydrophilic end bonds well to vinegar uncharged hydrophobic end bonds to oil
Vigorous beating produces many small oil droplets maximizing surface area for lecithin to act on and produce a stable emulsion
Stabilizers like sodium phosphate or metals are added to prevent separation (chefs use metal bowls)
hydrophilic
hydrophobic
Stereochemistry in Food Many food-specific compounds have a chiral
carbon atom and thus exist as two different enantiomers (optical isomers) Optical isomers are mirror images of one another ldquoOptical activityrdquo refers to the fact that the two mirror
image isomers rotate the direction of plane-polarized light in opposite directions
Enantiomers that rotate polarized light in a clockwise direction are said to be dextrorotatory (dex-tro-rota-tory) and have a + rotational value (d +) ndash In Latin dexter means ldquoright siderdquo
Enantiomers that rotate polarized light in an anti-clockwise direction are said to be laevorotatory (lay-vo-rota-tory) and have a ndash rotational value (l -) ndash In Latin laevus means ldquoleft siderdquo
There are two systems used to provide specific names to each enantiomeric form
Stereochemistry in Food Older system used for naming sugars and amino
acids Enantiomeric forms are labeled ldquoLrdquo and ldquoDrdquo
Again Laevus for left and Dexter for right Based off a compound called glyceraldehyde
chiral carbon
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Color Heme
Pigment found in red blood cells Structure is similar to chlorophyll but there is an iron
atom in the center of the porphyrin ring Found in the protein myoglobin responsible for
oxygen transport Bright red when bound to oxygen but slow process
of autoxidation converts iron from +2 to +3 changing color to brown (less desirable) (myoglobin metmyoglobin)
Color change can be prevented by vacuum packing or packing with an inert gas like CO2
Color
heme groupin myoglobin
Color Color in foods is a result of the structures seen in
anthocyanins carotenoids chlorophylls and hemes All of these structures include an extensive network of
delocalized pi-bonds Alternating single and double bonds is called a conjugated
system The greater the extent of pi bond delocalization the closer
together in energy bonding and antibonding orbitals become All molecules absorb light energy as it promotes e-s between
molecular orbitals (bonding and antibonding orbitals) ndash energy required is proportional to distance between orbitals (less distance = less energy)
As orbitals are close together in a conjugated system low energy light (in the visible region) is absorbed for e- promotion
Color in these groups is the product of visible light absorption - color we see is complementary to the color(s) absorbed
Molecules without an extensive delocalized pi bond network (conjugated system) lack color as orbitals are further apart and only higher energy light promotes e-s (ex the anthocyanin carbinol)
Color Some pigments are water soluble because the
structures contain a large amount of -OH groups (H-bonding) Anthocyanins
Some pigments are fat soluble (ie not water soluble) because their structures contain little or no -OH groups (no H-bonding) carotenoids
Color
Many synthetic dyes are biochemically active and could be potentially harmful
Short-term toxicity easy to test and categorize but long-term effects are more difficult to study
Use of dyes in foods must be regulated but regulations are not standardized internationally posing issues in trade
Color Cooking foods often leads to browning
Two processes responsible Maillard reactions ndash combination of sugars and
proteins Caramelization ndash dehydration of sugar
Both involve removal of water molecule(s)
Color Maillard reactions
Sugars and proteins within the food combine in a condensation reaction
Aldehyde group in sugar (O atom) combines with amino group in protein (2 H atoms)
Initial condensation products polymerize to form brown-colored melanoidins
Maillard reactions only happen gt 140deg C Rate depends on amino acid present (ex lysine
reacts faster than cysteine)
initialcondensationproduct
Color Caramelization
Happens in foods high in carbohydrates Sugars dehydrate (lose H2O) at high temperatures
leaving behind C (dark brown color)
Browning intensifies the longer food is cooked eventually burning it (pure carbon is black)
Rate depends on Sugar type (fructose in fruits caramelizes very quickly) pH ndash extremes (high and low) promote caramelization
Genetically Modified Foods
Produced when organisms with modified DNA are used in food production Used to
Provide pest or disease resistance Bt corn contains toxin from bacillis thuringiensis that kills
insect pests Fungal-resistant potatoes Nematode-resistant bananas (nematode = worm)
Improve quality and range of crop Development of higher-yielding rice varieties Development of corn that can grow in dryer environments
Produce medicines or other products in large quantities Use of chickens that have been modified to lay eggs
containing human interferon (combats tumors and viruses) Use of cows to produce milk rich in omega-3 fatty acids
(polyunsaturated fats essential to growth development brain function)
Moth larva
Genetically Modified Foods
Drawbacks Are GM foods safe Will GM food production alter the natural ecosystem Do we understand enough about genetic
modification GM foods
Can cause allergic reactions in some people Have a slightly different composition from natural foods ndash
alters diet Produce altered pollen ndash might escape and cross with natural
species Long-term effects might be catastrophic unknown so far
Texture Food texture is related to physical properties
Hardness Elasticity Viscosity
These properties can be altered by Cooking Use of dispersed systems
Dispersed system = a stabilized macroscopically homogeneous mixture of two immiscible phases
(this means two substances that would not ordinarily mix ldquoappear tordquo on a macroscopic level (although at the molecular level they are still separate)
Texture Many types of dispersed systems name depends on
the physical states of the substances mixed LiquidSolid or SolidLiquid
Solid particles suspended in a liquid is called a suspension
Ex Blood (blood cells suspended in plasma) Liquid dispersed throughout a solid medium is called a
gel Ex Fruit Jelly (water trapped in a solid protein matrix)
LiquidLiquid Stable blend of two liquids that donrsquot mix is called an
emulsion Ex Mayonaisse (oil droplets suspended in aqueous system)
LiquidGas or GasLiquid Gas bubbles trapped in liquid medium is called a foam
Ex Whipped cream or egg whites Liquid droplets suspended in gas are called aerosols
Ex Aromas from food carried through the air
Texture Dispersed systems will slowly separate over
time Separation can be slowed by adding emulsifiers
Emulsifiers are stabilizers used to keep immiscible substance together
Have surfactant capability (can bind to both substances in suspension)
Similar to micelles in the action of soaps
Ex Lecithin Found commonly in egg
yolks One end is highly charged
and water soluble (bonds toaqueous phase) the otheris not (bonds to non-aqueous phase)
Texture Lecithin in mayonnaise
Lecithin is the emulsifier Mayonnaise made by beating eggs with
vinegar and oil Lecithin is found in eggs ndash charged
hydrophilic end bonds well to vinegar uncharged hydrophobic end bonds to oil
Vigorous beating produces many small oil droplets maximizing surface area for lecithin to act on and produce a stable emulsion
Stabilizers like sodium phosphate or metals are added to prevent separation (chefs use metal bowls)
hydrophilic
hydrophobic
Stereochemistry in Food Many food-specific compounds have a chiral
carbon atom and thus exist as two different enantiomers (optical isomers) Optical isomers are mirror images of one another ldquoOptical activityrdquo refers to the fact that the two mirror
image isomers rotate the direction of plane-polarized light in opposite directions
Enantiomers that rotate polarized light in a clockwise direction are said to be dextrorotatory (dex-tro-rota-tory) and have a + rotational value (d +) ndash In Latin dexter means ldquoright siderdquo
Enantiomers that rotate polarized light in an anti-clockwise direction are said to be laevorotatory (lay-vo-rota-tory) and have a ndash rotational value (l -) ndash In Latin laevus means ldquoleft siderdquo
There are two systems used to provide specific names to each enantiomeric form
Stereochemistry in Food Older system used for naming sugars and amino
acids Enantiomeric forms are labeled ldquoLrdquo and ldquoDrdquo
Again Laevus for left and Dexter for right Based off a compound called glyceraldehyde
chiral carbon
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Color
heme groupin myoglobin
Color Color in foods is a result of the structures seen in
anthocyanins carotenoids chlorophylls and hemes All of these structures include an extensive network of
delocalized pi-bonds Alternating single and double bonds is called a conjugated
system The greater the extent of pi bond delocalization the closer
together in energy bonding and antibonding orbitals become All molecules absorb light energy as it promotes e-s between
molecular orbitals (bonding and antibonding orbitals) ndash energy required is proportional to distance between orbitals (less distance = less energy)
As orbitals are close together in a conjugated system low energy light (in the visible region) is absorbed for e- promotion
Color in these groups is the product of visible light absorption - color we see is complementary to the color(s) absorbed
Molecules without an extensive delocalized pi bond network (conjugated system) lack color as orbitals are further apart and only higher energy light promotes e-s (ex the anthocyanin carbinol)
Color Some pigments are water soluble because the
structures contain a large amount of -OH groups (H-bonding) Anthocyanins
Some pigments are fat soluble (ie not water soluble) because their structures contain little or no -OH groups (no H-bonding) carotenoids
Color
Many synthetic dyes are biochemically active and could be potentially harmful
Short-term toxicity easy to test and categorize but long-term effects are more difficult to study
Use of dyes in foods must be regulated but regulations are not standardized internationally posing issues in trade
Color Cooking foods often leads to browning
Two processes responsible Maillard reactions ndash combination of sugars and
proteins Caramelization ndash dehydration of sugar
Both involve removal of water molecule(s)
Color Maillard reactions
Sugars and proteins within the food combine in a condensation reaction
Aldehyde group in sugar (O atom) combines with amino group in protein (2 H atoms)
Initial condensation products polymerize to form brown-colored melanoidins
Maillard reactions only happen gt 140deg C Rate depends on amino acid present (ex lysine
reacts faster than cysteine)
initialcondensationproduct
Color Caramelization
Happens in foods high in carbohydrates Sugars dehydrate (lose H2O) at high temperatures
leaving behind C (dark brown color)
Browning intensifies the longer food is cooked eventually burning it (pure carbon is black)
Rate depends on Sugar type (fructose in fruits caramelizes very quickly) pH ndash extremes (high and low) promote caramelization
Genetically Modified Foods
Produced when organisms with modified DNA are used in food production Used to
Provide pest or disease resistance Bt corn contains toxin from bacillis thuringiensis that kills
insect pests Fungal-resistant potatoes Nematode-resistant bananas (nematode = worm)
Improve quality and range of crop Development of higher-yielding rice varieties Development of corn that can grow in dryer environments
Produce medicines or other products in large quantities Use of chickens that have been modified to lay eggs
containing human interferon (combats tumors and viruses) Use of cows to produce milk rich in omega-3 fatty acids
(polyunsaturated fats essential to growth development brain function)
Moth larva
Genetically Modified Foods
Drawbacks Are GM foods safe Will GM food production alter the natural ecosystem Do we understand enough about genetic
modification GM foods
Can cause allergic reactions in some people Have a slightly different composition from natural foods ndash
alters diet Produce altered pollen ndash might escape and cross with natural
species Long-term effects might be catastrophic unknown so far
Texture Food texture is related to physical properties
Hardness Elasticity Viscosity
These properties can be altered by Cooking Use of dispersed systems
Dispersed system = a stabilized macroscopically homogeneous mixture of two immiscible phases
(this means two substances that would not ordinarily mix ldquoappear tordquo on a macroscopic level (although at the molecular level they are still separate)
Texture Many types of dispersed systems name depends on
the physical states of the substances mixed LiquidSolid or SolidLiquid
Solid particles suspended in a liquid is called a suspension
Ex Blood (blood cells suspended in plasma) Liquid dispersed throughout a solid medium is called a
gel Ex Fruit Jelly (water trapped in a solid protein matrix)
LiquidLiquid Stable blend of two liquids that donrsquot mix is called an
emulsion Ex Mayonaisse (oil droplets suspended in aqueous system)
LiquidGas or GasLiquid Gas bubbles trapped in liquid medium is called a foam
Ex Whipped cream or egg whites Liquid droplets suspended in gas are called aerosols
Ex Aromas from food carried through the air
Texture Dispersed systems will slowly separate over
time Separation can be slowed by adding emulsifiers
Emulsifiers are stabilizers used to keep immiscible substance together
Have surfactant capability (can bind to both substances in suspension)
Similar to micelles in the action of soaps
Ex Lecithin Found commonly in egg
yolks One end is highly charged
and water soluble (bonds toaqueous phase) the otheris not (bonds to non-aqueous phase)
Texture Lecithin in mayonnaise
Lecithin is the emulsifier Mayonnaise made by beating eggs with
vinegar and oil Lecithin is found in eggs ndash charged
hydrophilic end bonds well to vinegar uncharged hydrophobic end bonds to oil
Vigorous beating produces many small oil droplets maximizing surface area for lecithin to act on and produce a stable emulsion
Stabilizers like sodium phosphate or metals are added to prevent separation (chefs use metal bowls)
hydrophilic
hydrophobic
Stereochemistry in Food Many food-specific compounds have a chiral
carbon atom and thus exist as two different enantiomers (optical isomers) Optical isomers are mirror images of one another ldquoOptical activityrdquo refers to the fact that the two mirror
image isomers rotate the direction of plane-polarized light in opposite directions
Enantiomers that rotate polarized light in a clockwise direction are said to be dextrorotatory (dex-tro-rota-tory) and have a + rotational value (d +) ndash In Latin dexter means ldquoright siderdquo
Enantiomers that rotate polarized light in an anti-clockwise direction are said to be laevorotatory (lay-vo-rota-tory) and have a ndash rotational value (l -) ndash In Latin laevus means ldquoleft siderdquo
There are two systems used to provide specific names to each enantiomeric form
Stereochemistry in Food Older system used for naming sugars and amino
acids Enantiomeric forms are labeled ldquoLrdquo and ldquoDrdquo
Again Laevus for left and Dexter for right Based off a compound called glyceraldehyde
chiral carbon
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Color Color in foods is a result of the structures seen in
anthocyanins carotenoids chlorophylls and hemes All of these structures include an extensive network of
delocalized pi-bonds Alternating single and double bonds is called a conjugated
system The greater the extent of pi bond delocalization the closer
together in energy bonding and antibonding orbitals become All molecules absorb light energy as it promotes e-s between
molecular orbitals (bonding and antibonding orbitals) ndash energy required is proportional to distance between orbitals (less distance = less energy)
As orbitals are close together in a conjugated system low energy light (in the visible region) is absorbed for e- promotion
Color in these groups is the product of visible light absorption - color we see is complementary to the color(s) absorbed
Molecules without an extensive delocalized pi bond network (conjugated system) lack color as orbitals are further apart and only higher energy light promotes e-s (ex the anthocyanin carbinol)
Color Some pigments are water soluble because the
structures contain a large amount of -OH groups (H-bonding) Anthocyanins
Some pigments are fat soluble (ie not water soluble) because their structures contain little or no -OH groups (no H-bonding) carotenoids
Color
Many synthetic dyes are biochemically active and could be potentially harmful
Short-term toxicity easy to test and categorize but long-term effects are more difficult to study
Use of dyes in foods must be regulated but regulations are not standardized internationally posing issues in trade
Color Cooking foods often leads to browning
Two processes responsible Maillard reactions ndash combination of sugars and
proteins Caramelization ndash dehydration of sugar
Both involve removal of water molecule(s)
Color Maillard reactions
Sugars and proteins within the food combine in a condensation reaction
Aldehyde group in sugar (O atom) combines with amino group in protein (2 H atoms)
Initial condensation products polymerize to form brown-colored melanoidins
Maillard reactions only happen gt 140deg C Rate depends on amino acid present (ex lysine
reacts faster than cysteine)
initialcondensationproduct
Color Caramelization
Happens in foods high in carbohydrates Sugars dehydrate (lose H2O) at high temperatures
leaving behind C (dark brown color)
Browning intensifies the longer food is cooked eventually burning it (pure carbon is black)
Rate depends on Sugar type (fructose in fruits caramelizes very quickly) pH ndash extremes (high and low) promote caramelization
Genetically Modified Foods
Produced when organisms with modified DNA are used in food production Used to
Provide pest or disease resistance Bt corn contains toxin from bacillis thuringiensis that kills
insect pests Fungal-resistant potatoes Nematode-resistant bananas (nematode = worm)
Improve quality and range of crop Development of higher-yielding rice varieties Development of corn that can grow in dryer environments
Produce medicines or other products in large quantities Use of chickens that have been modified to lay eggs
containing human interferon (combats tumors and viruses) Use of cows to produce milk rich in omega-3 fatty acids
(polyunsaturated fats essential to growth development brain function)
Moth larva
Genetically Modified Foods
Drawbacks Are GM foods safe Will GM food production alter the natural ecosystem Do we understand enough about genetic
modification GM foods
Can cause allergic reactions in some people Have a slightly different composition from natural foods ndash
alters diet Produce altered pollen ndash might escape and cross with natural
species Long-term effects might be catastrophic unknown so far
Texture Food texture is related to physical properties
Hardness Elasticity Viscosity
These properties can be altered by Cooking Use of dispersed systems
Dispersed system = a stabilized macroscopically homogeneous mixture of two immiscible phases
(this means two substances that would not ordinarily mix ldquoappear tordquo on a macroscopic level (although at the molecular level they are still separate)
Texture Many types of dispersed systems name depends on
the physical states of the substances mixed LiquidSolid or SolidLiquid
Solid particles suspended in a liquid is called a suspension
Ex Blood (blood cells suspended in plasma) Liquid dispersed throughout a solid medium is called a
gel Ex Fruit Jelly (water trapped in a solid protein matrix)
LiquidLiquid Stable blend of two liquids that donrsquot mix is called an
emulsion Ex Mayonaisse (oil droplets suspended in aqueous system)
LiquidGas or GasLiquid Gas bubbles trapped in liquid medium is called a foam
Ex Whipped cream or egg whites Liquid droplets suspended in gas are called aerosols
Ex Aromas from food carried through the air
Texture Dispersed systems will slowly separate over
time Separation can be slowed by adding emulsifiers
Emulsifiers are stabilizers used to keep immiscible substance together
Have surfactant capability (can bind to both substances in suspension)
Similar to micelles in the action of soaps
Ex Lecithin Found commonly in egg
yolks One end is highly charged
and water soluble (bonds toaqueous phase) the otheris not (bonds to non-aqueous phase)
Texture Lecithin in mayonnaise
Lecithin is the emulsifier Mayonnaise made by beating eggs with
vinegar and oil Lecithin is found in eggs ndash charged
hydrophilic end bonds well to vinegar uncharged hydrophobic end bonds to oil
Vigorous beating produces many small oil droplets maximizing surface area for lecithin to act on and produce a stable emulsion
Stabilizers like sodium phosphate or metals are added to prevent separation (chefs use metal bowls)
hydrophilic
hydrophobic
Stereochemistry in Food Many food-specific compounds have a chiral
carbon atom and thus exist as two different enantiomers (optical isomers) Optical isomers are mirror images of one another ldquoOptical activityrdquo refers to the fact that the two mirror
image isomers rotate the direction of plane-polarized light in opposite directions
Enantiomers that rotate polarized light in a clockwise direction are said to be dextrorotatory (dex-tro-rota-tory) and have a + rotational value (d +) ndash In Latin dexter means ldquoright siderdquo
Enantiomers that rotate polarized light in an anti-clockwise direction are said to be laevorotatory (lay-vo-rota-tory) and have a ndash rotational value (l -) ndash In Latin laevus means ldquoleft siderdquo
There are two systems used to provide specific names to each enantiomeric form
Stereochemistry in Food Older system used for naming sugars and amino
acids Enantiomeric forms are labeled ldquoLrdquo and ldquoDrdquo
Again Laevus for left and Dexter for right Based off a compound called glyceraldehyde
chiral carbon
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Color Some pigments are water soluble because the
structures contain a large amount of -OH groups (H-bonding) Anthocyanins
Some pigments are fat soluble (ie not water soluble) because their structures contain little or no -OH groups (no H-bonding) carotenoids
Color
Many synthetic dyes are biochemically active and could be potentially harmful
Short-term toxicity easy to test and categorize but long-term effects are more difficult to study
Use of dyes in foods must be regulated but regulations are not standardized internationally posing issues in trade
Color Cooking foods often leads to browning
Two processes responsible Maillard reactions ndash combination of sugars and
proteins Caramelization ndash dehydration of sugar
Both involve removal of water molecule(s)
Color Maillard reactions
Sugars and proteins within the food combine in a condensation reaction
Aldehyde group in sugar (O atom) combines with amino group in protein (2 H atoms)
Initial condensation products polymerize to form brown-colored melanoidins
Maillard reactions only happen gt 140deg C Rate depends on amino acid present (ex lysine
reacts faster than cysteine)
initialcondensationproduct
Color Caramelization
Happens in foods high in carbohydrates Sugars dehydrate (lose H2O) at high temperatures
leaving behind C (dark brown color)
Browning intensifies the longer food is cooked eventually burning it (pure carbon is black)
Rate depends on Sugar type (fructose in fruits caramelizes very quickly) pH ndash extremes (high and low) promote caramelization
Genetically Modified Foods
Produced when organisms with modified DNA are used in food production Used to
Provide pest or disease resistance Bt corn contains toxin from bacillis thuringiensis that kills
insect pests Fungal-resistant potatoes Nematode-resistant bananas (nematode = worm)
Improve quality and range of crop Development of higher-yielding rice varieties Development of corn that can grow in dryer environments
Produce medicines or other products in large quantities Use of chickens that have been modified to lay eggs
containing human interferon (combats tumors and viruses) Use of cows to produce milk rich in omega-3 fatty acids
(polyunsaturated fats essential to growth development brain function)
Moth larva
Genetically Modified Foods
Drawbacks Are GM foods safe Will GM food production alter the natural ecosystem Do we understand enough about genetic
modification GM foods
Can cause allergic reactions in some people Have a slightly different composition from natural foods ndash
alters diet Produce altered pollen ndash might escape and cross with natural
species Long-term effects might be catastrophic unknown so far
Texture Food texture is related to physical properties
Hardness Elasticity Viscosity
These properties can be altered by Cooking Use of dispersed systems
Dispersed system = a stabilized macroscopically homogeneous mixture of two immiscible phases
(this means two substances that would not ordinarily mix ldquoappear tordquo on a macroscopic level (although at the molecular level they are still separate)
Texture Many types of dispersed systems name depends on
the physical states of the substances mixed LiquidSolid or SolidLiquid
Solid particles suspended in a liquid is called a suspension
Ex Blood (blood cells suspended in plasma) Liquid dispersed throughout a solid medium is called a
gel Ex Fruit Jelly (water trapped in a solid protein matrix)
LiquidLiquid Stable blend of two liquids that donrsquot mix is called an
emulsion Ex Mayonaisse (oil droplets suspended in aqueous system)
LiquidGas or GasLiquid Gas bubbles trapped in liquid medium is called a foam
Ex Whipped cream or egg whites Liquid droplets suspended in gas are called aerosols
Ex Aromas from food carried through the air
Texture Dispersed systems will slowly separate over
time Separation can be slowed by adding emulsifiers
Emulsifiers are stabilizers used to keep immiscible substance together
Have surfactant capability (can bind to both substances in suspension)
Similar to micelles in the action of soaps
Ex Lecithin Found commonly in egg
yolks One end is highly charged
and water soluble (bonds toaqueous phase) the otheris not (bonds to non-aqueous phase)
Texture Lecithin in mayonnaise
Lecithin is the emulsifier Mayonnaise made by beating eggs with
vinegar and oil Lecithin is found in eggs ndash charged
hydrophilic end bonds well to vinegar uncharged hydrophobic end bonds to oil
Vigorous beating produces many small oil droplets maximizing surface area for lecithin to act on and produce a stable emulsion
Stabilizers like sodium phosphate or metals are added to prevent separation (chefs use metal bowls)
hydrophilic
hydrophobic
Stereochemistry in Food Many food-specific compounds have a chiral
carbon atom and thus exist as two different enantiomers (optical isomers) Optical isomers are mirror images of one another ldquoOptical activityrdquo refers to the fact that the two mirror
image isomers rotate the direction of plane-polarized light in opposite directions
Enantiomers that rotate polarized light in a clockwise direction are said to be dextrorotatory (dex-tro-rota-tory) and have a + rotational value (d +) ndash In Latin dexter means ldquoright siderdquo
Enantiomers that rotate polarized light in an anti-clockwise direction are said to be laevorotatory (lay-vo-rota-tory) and have a ndash rotational value (l -) ndash In Latin laevus means ldquoleft siderdquo
There are two systems used to provide specific names to each enantiomeric form
Stereochemistry in Food Older system used for naming sugars and amino
acids Enantiomeric forms are labeled ldquoLrdquo and ldquoDrdquo
Again Laevus for left and Dexter for right Based off a compound called glyceraldehyde
chiral carbon
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Color
Many synthetic dyes are biochemically active and could be potentially harmful
Short-term toxicity easy to test and categorize but long-term effects are more difficult to study
Use of dyes in foods must be regulated but regulations are not standardized internationally posing issues in trade
Color Cooking foods often leads to browning
Two processes responsible Maillard reactions ndash combination of sugars and
proteins Caramelization ndash dehydration of sugar
Both involve removal of water molecule(s)
Color Maillard reactions
Sugars and proteins within the food combine in a condensation reaction
Aldehyde group in sugar (O atom) combines with amino group in protein (2 H atoms)
Initial condensation products polymerize to form brown-colored melanoidins
Maillard reactions only happen gt 140deg C Rate depends on amino acid present (ex lysine
reacts faster than cysteine)
initialcondensationproduct
Color Caramelization
Happens in foods high in carbohydrates Sugars dehydrate (lose H2O) at high temperatures
leaving behind C (dark brown color)
Browning intensifies the longer food is cooked eventually burning it (pure carbon is black)
Rate depends on Sugar type (fructose in fruits caramelizes very quickly) pH ndash extremes (high and low) promote caramelization
Genetically Modified Foods
Produced when organisms with modified DNA are used in food production Used to
Provide pest or disease resistance Bt corn contains toxin from bacillis thuringiensis that kills
insect pests Fungal-resistant potatoes Nematode-resistant bananas (nematode = worm)
Improve quality and range of crop Development of higher-yielding rice varieties Development of corn that can grow in dryer environments
Produce medicines or other products in large quantities Use of chickens that have been modified to lay eggs
containing human interferon (combats tumors and viruses) Use of cows to produce milk rich in omega-3 fatty acids
(polyunsaturated fats essential to growth development brain function)
Moth larva
Genetically Modified Foods
Drawbacks Are GM foods safe Will GM food production alter the natural ecosystem Do we understand enough about genetic
modification GM foods
Can cause allergic reactions in some people Have a slightly different composition from natural foods ndash
alters diet Produce altered pollen ndash might escape and cross with natural
species Long-term effects might be catastrophic unknown so far
Texture Food texture is related to physical properties
Hardness Elasticity Viscosity
These properties can be altered by Cooking Use of dispersed systems
Dispersed system = a stabilized macroscopically homogeneous mixture of two immiscible phases
(this means two substances that would not ordinarily mix ldquoappear tordquo on a macroscopic level (although at the molecular level they are still separate)
Texture Many types of dispersed systems name depends on
the physical states of the substances mixed LiquidSolid or SolidLiquid
Solid particles suspended in a liquid is called a suspension
Ex Blood (blood cells suspended in plasma) Liquid dispersed throughout a solid medium is called a
gel Ex Fruit Jelly (water trapped in a solid protein matrix)
LiquidLiquid Stable blend of two liquids that donrsquot mix is called an
emulsion Ex Mayonaisse (oil droplets suspended in aqueous system)
LiquidGas or GasLiquid Gas bubbles trapped in liquid medium is called a foam
Ex Whipped cream or egg whites Liquid droplets suspended in gas are called aerosols
Ex Aromas from food carried through the air
Texture Dispersed systems will slowly separate over
time Separation can be slowed by adding emulsifiers
Emulsifiers are stabilizers used to keep immiscible substance together
Have surfactant capability (can bind to both substances in suspension)
Similar to micelles in the action of soaps
Ex Lecithin Found commonly in egg
yolks One end is highly charged
and water soluble (bonds toaqueous phase) the otheris not (bonds to non-aqueous phase)
Texture Lecithin in mayonnaise
Lecithin is the emulsifier Mayonnaise made by beating eggs with
vinegar and oil Lecithin is found in eggs ndash charged
hydrophilic end bonds well to vinegar uncharged hydrophobic end bonds to oil
Vigorous beating produces many small oil droplets maximizing surface area for lecithin to act on and produce a stable emulsion
Stabilizers like sodium phosphate or metals are added to prevent separation (chefs use metal bowls)
hydrophilic
hydrophobic
Stereochemistry in Food Many food-specific compounds have a chiral
carbon atom and thus exist as two different enantiomers (optical isomers) Optical isomers are mirror images of one another ldquoOptical activityrdquo refers to the fact that the two mirror
image isomers rotate the direction of plane-polarized light in opposite directions
Enantiomers that rotate polarized light in a clockwise direction are said to be dextrorotatory (dex-tro-rota-tory) and have a + rotational value (d +) ndash In Latin dexter means ldquoright siderdquo
Enantiomers that rotate polarized light in an anti-clockwise direction are said to be laevorotatory (lay-vo-rota-tory) and have a ndash rotational value (l -) ndash In Latin laevus means ldquoleft siderdquo
There are two systems used to provide specific names to each enantiomeric form
Stereochemistry in Food Older system used for naming sugars and amino
acids Enantiomeric forms are labeled ldquoLrdquo and ldquoDrdquo
Again Laevus for left and Dexter for right Based off a compound called glyceraldehyde
chiral carbon
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Color Cooking foods often leads to browning
Two processes responsible Maillard reactions ndash combination of sugars and
proteins Caramelization ndash dehydration of sugar
Both involve removal of water molecule(s)
Color Maillard reactions
Sugars and proteins within the food combine in a condensation reaction
Aldehyde group in sugar (O atom) combines with amino group in protein (2 H atoms)
Initial condensation products polymerize to form brown-colored melanoidins
Maillard reactions only happen gt 140deg C Rate depends on amino acid present (ex lysine
reacts faster than cysteine)
initialcondensationproduct
Color Caramelization
Happens in foods high in carbohydrates Sugars dehydrate (lose H2O) at high temperatures
leaving behind C (dark brown color)
Browning intensifies the longer food is cooked eventually burning it (pure carbon is black)
Rate depends on Sugar type (fructose in fruits caramelizes very quickly) pH ndash extremes (high and low) promote caramelization
Genetically Modified Foods
Produced when organisms with modified DNA are used in food production Used to
Provide pest or disease resistance Bt corn contains toxin from bacillis thuringiensis that kills
insect pests Fungal-resistant potatoes Nematode-resistant bananas (nematode = worm)
Improve quality and range of crop Development of higher-yielding rice varieties Development of corn that can grow in dryer environments
Produce medicines or other products in large quantities Use of chickens that have been modified to lay eggs
containing human interferon (combats tumors and viruses) Use of cows to produce milk rich in omega-3 fatty acids
(polyunsaturated fats essential to growth development brain function)
Moth larva
Genetically Modified Foods
Drawbacks Are GM foods safe Will GM food production alter the natural ecosystem Do we understand enough about genetic
modification GM foods
Can cause allergic reactions in some people Have a slightly different composition from natural foods ndash
alters diet Produce altered pollen ndash might escape and cross with natural
species Long-term effects might be catastrophic unknown so far
Texture Food texture is related to physical properties
Hardness Elasticity Viscosity
These properties can be altered by Cooking Use of dispersed systems
Dispersed system = a stabilized macroscopically homogeneous mixture of two immiscible phases
(this means two substances that would not ordinarily mix ldquoappear tordquo on a macroscopic level (although at the molecular level they are still separate)
Texture Many types of dispersed systems name depends on
the physical states of the substances mixed LiquidSolid or SolidLiquid
Solid particles suspended in a liquid is called a suspension
Ex Blood (blood cells suspended in plasma) Liquid dispersed throughout a solid medium is called a
gel Ex Fruit Jelly (water trapped in a solid protein matrix)
LiquidLiquid Stable blend of two liquids that donrsquot mix is called an
emulsion Ex Mayonaisse (oil droplets suspended in aqueous system)
LiquidGas or GasLiquid Gas bubbles trapped in liquid medium is called a foam
Ex Whipped cream or egg whites Liquid droplets suspended in gas are called aerosols
Ex Aromas from food carried through the air
Texture Dispersed systems will slowly separate over
time Separation can be slowed by adding emulsifiers
Emulsifiers are stabilizers used to keep immiscible substance together
Have surfactant capability (can bind to both substances in suspension)
Similar to micelles in the action of soaps
Ex Lecithin Found commonly in egg
yolks One end is highly charged
and water soluble (bonds toaqueous phase) the otheris not (bonds to non-aqueous phase)
Texture Lecithin in mayonnaise
Lecithin is the emulsifier Mayonnaise made by beating eggs with
vinegar and oil Lecithin is found in eggs ndash charged
hydrophilic end bonds well to vinegar uncharged hydrophobic end bonds to oil
Vigorous beating produces many small oil droplets maximizing surface area for lecithin to act on and produce a stable emulsion
Stabilizers like sodium phosphate or metals are added to prevent separation (chefs use metal bowls)
hydrophilic
hydrophobic
Stereochemistry in Food Many food-specific compounds have a chiral
carbon atom and thus exist as two different enantiomers (optical isomers) Optical isomers are mirror images of one another ldquoOptical activityrdquo refers to the fact that the two mirror
image isomers rotate the direction of plane-polarized light in opposite directions
Enantiomers that rotate polarized light in a clockwise direction are said to be dextrorotatory (dex-tro-rota-tory) and have a + rotational value (d +) ndash In Latin dexter means ldquoright siderdquo
Enantiomers that rotate polarized light in an anti-clockwise direction are said to be laevorotatory (lay-vo-rota-tory) and have a ndash rotational value (l -) ndash In Latin laevus means ldquoleft siderdquo
There are two systems used to provide specific names to each enantiomeric form
Stereochemistry in Food Older system used for naming sugars and amino
acids Enantiomeric forms are labeled ldquoLrdquo and ldquoDrdquo
Again Laevus for left and Dexter for right Based off a compound called glyceraldehyde
chiral carbon
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Color Maillard reactions
Sugars and proteins within the food combine in a condensation reaction
Aldehyde group in sugar (O atom) combines with amino group in protein (2 H atoms)
Initial condensation products polymerize to form brown-colored melanoidins
Maillard reactions only happen gt 140deg C Rate depends on amino acid present (ex lysine
reacts faster than cysteine)
initialcondensationproduct
Color Caramelization
Happens in foods high in carbohydrates Sugars dehydrate (lose H2O) at high temperatures
leaving behind C (dark brown color)
Browning intensifies the longer food is cooked eventually burning it (pure carbon is black)
Rate depends on Sugar type (fructose in fruits caramelizes very quickly) pH ndash extremes (high and low) promote caramelization
Genetically Modified Foods
Produced when organisms with modified DNA are used in food production Used to
Provide pest or disease resistance Bt corn contains toxin from bacillis thuringiensis that kills
insect pests Fungal-resistant potatoes Nematode-resistant bananas (nematode = worm)
Improve quality and range of crop Development of higher-yielding rice varieties Development of corn that can grow in dryer environments
Produce medicines or other products in large quantities Use of chickens that have been modified to lay eggs
containing human interferon (combats tumors and viruses) Use of cows to produce milk rich in omega-3 fatty acids
(polyunsaturated fats essential to growth development brain function)
Moth larva
Genetically Modified Foods
Drawbacks Are GM foods safe Will GM food production alter the natural ecosystem Do we understand enough about genetic
modification GM foods
Can cause allergic reactions in some people Have a slightly different composition from natural foods ndash
alters diet Produce altered pollen ndash might escape and cross with natural
species Long-term effects might be catastrophic unknown so far
Texture Food texture is related to physical properties
Hardness Elasticity Viscosity
These properties can be altered by Cooking Use of dispersed systems
Dispersed system = a stabilized macroscopically homogeneous mixture of two immiscible phases
(this means two substances that would not ordinarily mix ldquoappear tordquo on a macroscopic level (although at the molecular level they are still separate)
Texture Many types of dispersed systems name depends on
the physical states of the substances mixed LiquidSolid or SolidLiquid
Solid particles suspended in a liquid is called a suspension
Ex Blood (blood cells suspended in plasma) Liquid dispersed throughout a solid medium is called a
gel Ex Fruit Jelly (water trapped in a solid protein matrix)
LiquidLiquid Stable blend of two liquids that donrsquot mix is called an
emulsion Ex Mayonaisse (oil droplets suspended in aqueous system)
LiquidGas or GasLiquid Gas bubbles trapped in liquid medium is called a foam
Ex Whipped cream or egg whites Liquid droplets suspended in gas are called aerosols
Ex Aromas from food carried through the air
Texture Dispersed systems will slowly separate over
time Separation can be slowed by adding emulsifiers
Emulsifiers are stabilizers used to keep immiscible substance together
Have surfactant capability (can bind to both substances in suspension)
Similar to micelles in the action of soaps
Ex Lecithin Found commonly in egg
yolks One end is highly charged
and water soluble (bonds toaqueous phase) the otheris not (bonds to non-aqueous phase)
Texture Lecithin in mayonnaise
Lecithin is the emulsifier Mayonnaise made by beating eggs with
vinegar and oil Lecithin is found in eggs ndash charged
hydrophilic end bonds well to vinegar uncharged hydrophobic end bonds to oil
Vigorous beating produces many small oil droplets maximizing surface area for lecithin to act on and produce a stable emulsion
Stabilizers like sodium phosphate or metals are added to prevent separation (chefs use metal bowls)
hydrophilic
hydrophobic
Stereochemistry in Food Many food-specific compounds have a chiral
carbon atom and thus exist as two different enantiomers (optical isomers) Optical isomers are mirror images of one another ldquoOptical activityrdquo refers to the fact that the two mirror
image isomers rotate the direction of plane-polarized light in opposite directions
Enantiomers that rotate polarized light in a clockwise direction are said to be dextrorotatory (dex-tro-rota-tory) and have a + rotational value (d +) ndash In Latin dexter means ldquoright siderdquo
Enantiomers that rotate polarized light in an anti-clockwise direction are said to be laevorotatory (lay-vo-rota-tory) and have a ndash rotational value (l -) ndash In Latin laevus means ldquoleft siderdquo
There are two systems used to provide specific names to each enantiomeric form
Stereochemistry in Food Older system used for naming sugars and amino
acids Enantiomeric forms are labeled ldquoLrdquo and ldquoDrdquo
Again Laevus for left and Dexter for right Based off a compound called glyceraldehyde
chiral carbon
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Color Caramelization
Happens in foods high in carbohydrates Sugars dehydrate (lose H2O) at high temperatures
leaving behind C (dark brown color)
Browning intensifies the longer food is cooked eventually burning it (pure carbon is black)
Rate depends on Sugar type (fructose in fruits caramelizes very quickly) pH ndash extremes (high and low) promote caramelization
Genetically Modified Foods
Produced when organisms with modified DNA are used in food production Used to
Provide pest or disease resistance Bt corn contains toxin from bacillis thuringiensis that kills
insect pests Fungal-resistant potatoes Nematode-resistant bananas (nematode = worm)
Improve quality and range of crop Development of higher-yielding rice varieties Development of corn that can grow in dryer environments
Produce medicines or other products in large quantities Use of chickens that have been modified to lay eggs
containing human interferon (combats tumors and viruses) Use of cows to produce milk rich in omega-3 fatty acids
(polyunsaturated fats essential to growth development brain function)
Moth larva
Genetically Modified Foods
Drawbacks Are GM foods safe Will GM food production alter the natural ecosystem Do we understand enough about genetic
modification GM foods
Can cause allergic reactions in some people Have a slightly different composition from natural foods ndash
alters diet Produce altered pollen ndash might escape and cross with natural
species Long-term effects might be catastrophic unknown so far
Texture Food texture is related to physical properties
Hardness Elasticity Viscosity
These properties can be altered by Cooking Use of dispersed systems
Dispersed system = a stabilized macroscopically homogeneous mixture of two immiscible phases
(this means two substances that would not ordinarily mix ldquoappear tordquo on a macroscopic level (although at the molecular level they are still separate)
Texture Many types of dispersed systems name depends on
the physical states of the substances mixed LiquidSolid or SolidLiquid
Solid particles suspended in a liquid is called a suspension
Ex Blood (blood cells suspended in plasma) Liquid dispersed throughout a solid medium is called a
gel Ex Fruit Jelly (water trapped in a solid protein matrix)
LiquidLiquid Stable blend of two liquids that donrsquot mix is called an
emulsion Ex Mayonaisse (oil droplets suspended in aqueous system)
LiquidGas or GasLiquid Gas bubbles trapped in liquid medium is called a foam
Ex Whipped cream or egg whites Liquid droplets suspended in gas are called aerosols
Ex Aromas from food carried through the air
Texture Dispersed systems will slowly separate over
time Separation can be slowed by adding emulsifiers
Emulsifiers are stabilizers used to keep immiscible substance together
Have surfactant capability (can bind to both substances in suspension)
Similar to micelles in the action of soaps
Ex Lecithin Found commonly in egg
yolks One end is highly charged
and water soluble (bonds toaqueous phase) the otheris not (bonds to non-aqueous phase)
Texture Lecithin in mayonnaise
Lecithin is the emulsifier Mayonnaise made by beating eggs with
vinegar and oil Lecithin is found in eggs ndash charged
hydrophilic end bonds well to vinegar uncharged hydrophobic end bonds to oil
Vigorous beating produces many small oil droplets maximizing surface area for lecithin to act on and produce a stable emulsion
Stabilizers like sodium phosphate or metals are added to prevent separation (chefs use metal bowls)
hydrophilic
hydrophobic
Stereochemistry in Food Many food-specific compounds have a chiral
carbon atom and thus exist as two different enantiomers (optical isomers) Optical isomers are mirror images of one another ldquoOptical activityrdquo refers to the fact that the two mirror
image isomers rotate the direction of plane-polarized light in opposite directions
Enantiomers that rotate polarized light in a clockwise direction are said to be dextrorotatory (dex-tro-rota-tory) and have a + rotational value (d +) ndash In Latin dexter means ldquoright siderdquo
Enantiomers that rotate polarized light in an anti-clockwise direction are said to be laevorotatory (lay-vo-rota-tory) and have a ndash rotational value (l -) ndash In Latin laevus means ldquoleft siderdquo
There are two systems used to provide specific names to each enantiomeric form
Stereochemistry in Food Older system used for naming sugars and amino
acids Enantiomeric forms are labeled ldquoLrdquo and ldquoDrdquo
Again Laevus for left and Dexter for right Based off a compound called glyceraldehyde
chiral carbon
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Genetically Modified Foods
Produced when organisms with modified DNA are used in food production Used to
Provide pest or disease resistance Bt corn contains toxin from bacillis thuringiensis that kills
insect pests Fungal-resistant potatoes Nematode-resistant bananas (nematode = worm)
Improve quality and range of crop Development of higher-yielding rice varieties Development of corn that can grow in dryer environments
Produce medicines or other products in large quantities Use of chickens that have been modified to lay eggs
containing human interferon (combats tumors and viruses) Use of cows to produce milk rich in omega-3 fatty acids
(polyunsaturated fats essential to growth development brain function)
Moth larva
Genetically Modified Foods
Drawbacks Are GM foods safe Will GM food production alter the natural ecosystem Do we understand enough about genetic
modification GM foods
Can cause allergic reactions in some people Have a slightly different composition from natural foods ndash
alters diet Produce altered pollen ndash might escape and cross with natural
species Long-term effects might be catastrophic unknown so far
Texture Food texture is related to physical properties
Hardness Elasticity Viscosity
These properties can be altered by Cooking Use of dispersed systems
Dispersed system = a stabilized macroscopically homogeneous mixture of two immiscible phases
(this means two substances that would not ordinarily mix ldquoappear tordquo on a macroscopic level (although at the molecular level they are still separate)
Texture Many types of dispersed systems name depends on
the physical states of the substances mixed LiquidSolid or SolidLiquid
Solid particles suspended in a liquid is called a suspension
Ex Blood (blood cells suspended in plasma) Liquid dispersed throughout a solid medium is called a
gel Ex Fruit Jelly (water trapped in a solid protein matrix)
LiquidLiquid Stable blend of two liquids that donrsquot mix is called an
emulsion Ex Mayonaisse (oil droplets suspended in aqueous system)
LiquidGas or GasLiquid Gas bubbles trapped in liquid medium is called a foam
Ex Whipped cream or egg whites Liquid droplets suspended in gas are called aerosols
Ex Aromas from food carried through the air
Texture Dispersed systems will slowly separate over
time Separation can be slowed by adding emulsifiers
Emulsifiers are stabilizers used to keep immiscible substance together
Have surfactant capability (can bind to both substances in suspension)
Similar to micelles in the action of soaps
Ex Lecithin Found commonly in egg
yolks One end is highly charged
and water soluble (bonds toaqueous phase) the otheris not (bonds to non-aqueous phase)
Texture Lecithin in mayonnaise
Lecithin is the emulsifier Mayonnaise made by beating eggs with
vinegar and oil Lecithin is found in eggs ndash charged
hydrophilic end bonds well to vinegar uncharged hydrophobic end bonds to oil
Vigorous beating produces many small oil droplets maximizing surface area for lecithin to act on and produce a stable emulsion
Stabilizers like sodium phosphate or metals are added to prevent separation (chefs use metal bowls)
hydrophilic
hydrophobic
Stereochemistry in Food Many food-specific compounds have a chiral
carbon atom and thus exist as two different enantiomers (optical isomers) Optical isomers are mirror images of one another ldquoOptical activityrdquo refers to the fact that the two mirror
image isomers rotate the direction of plane-polarized light in opposite directions
Enantiomers that rotate polarized light in a clockwise direction are said to be dextrorotatory (dex-tro-rota-tory) and have a + rotational value (d +) ndash In Latin dexter means ldquoright siderdquo
Enantiomers that rotate polarized light in an anti-clockwise direction are said to be laevorotatory (lay-vo-rota-tory) and have a ndash rotational value (l -) ndash In Latin laevus means ldquoleft siderdquo
There are two systems used to provide specific names to each enantiomeric form
Stereochemistry in Food Older system used for naming sugars and amino
acids Enantiomeric forms are labeled ldquoLrdquo and ldquoDrdquo
Again Laevus for left and Dexter for right Based off a compound called glyceraldehyde
chiral carbon
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Genetically Modified Foods
Drawbacks Are GM foods safe Will GM food production alter the natural ecosystem Do we understand enough about genetic
modification GM foods
Can cause allergic reactions in some people Have a slightly different composition from natural foods ndash
alters diet Produce altered pollen ndash might escape and cross with natural
species Long-term effects might be catastrophic unknown so far
Texture Food texture is related to physical properties
Hardness Elasticity Viscosity
These properties can be altered by Cooking Use of dispersed systems
Dispersed system = a stabilized macroscopically homogeneous mixture of two immiscible phases
(this means two substances that would not ordinarily mix ldquoappear tordquo on a macroscopic level (although at the molecular level they are still separate)
Texture Many types of dispersed systems name depends on
the physical states of the substances mixed LiquidSolid or SolidLiquid
Solid particles suspended in a liquid is called a suspension
Ex Blood (blood cells suspended in plasma) Liquid dispersed throughout a solid medium is called a
gel Ex Fruit Jelly (water trapped in a solid protein matrix)
LiquidLiquid Stable blend of two liquids that donrsquot mix is called an
emulsion Ex Mayonaisse (oil droplets suspended in aqueous system)
LiquidGas or GasLiquid Gas bubbles trapped in liquid medium is called a foam
Ex Whipped cream or egg whites Liquid droplets suspended in gas are called aerosols
Ex Aromas from food carried through the air
Texture Dispersed systems will slowly separate over
time Separation can be slowed by adding emulsifiers
Emulsifiers are stabilizers used to keep immiscible substance together
Have surfactant capability (can bind to both substances in suspension)
Similar to micelles in the action of soaps
Ex Lecithin Found commonly in egg
yolks One end is highly charged
and water soluble (bonds toaqueous phase) the otheris not (bonds to non-aqueous phase)
Texture Lecithin in mayonnaise
Lecithin is the emulsifier Mayonnaise made by beating eggs with
vinegar and oil Lecithin is found in eggs ndash charged
hydrophilic end bonds well to vinegar uncharged hydrophobic end bonds to oil
Vigorous beating produces many small oil droplets maximizing surface area for lecithin to act on and produce a stable emulsion
Stabilizers like sodium phosphate or metals are added to prevent separation (chefs use metal bowls)
hydrophilic
hydrophobic
Stereochemistry in Food Many food-specific compounds have a chiral
carbon atom and thus exist as two different enantiomers (optical isomers) Optical isomers are mirror images of one another ldquoOptical activityrdquo refers to the fact that the two mirror
image isomers rotate the direction of plane-polarized light in opposite directions
Enantiomers that rotate polarized light in a clockwise direction are said to be dextrorotatory (dex-tro-rota-tory) and have a + rotational value (d +) ndash In Latin dexter means ldquoright siderdquo
Enantiomers that rotate polarized light in an anti-clockwise direction are said to be laevorotatory (lay-vo-rota-tory) and have a ndash rotational value (l -) ndash In Latin laevus means ldquoleft siderdquo
There are two systems used to provide specific names to each enantiomeric form
Stereochemistry in Food Older system used for naming sugars and amino
acids Enantiomeric forms are labeled ldquoLrdquo and ldquoDrdquo
Again Laevus for left and Dexter for right Based off a compound called glyceraldehyde
chiral carbon
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Texture Food texture is related to physical properties
Hardness Elasticity Viscosity
These properties can be altered by Cooking Use of dispersed systems
Dispersed system = a stabilized macroscopically homogeneous mixture of two immiscible phases
(this means two substances that would not ordinarily mix ldquoappear tordquo on a macroscopic level (although at the molecular level they are still separate)
Texture Many types of dispersed systems name depends on
the physical states of the substances mixed LiquidSolid or SolidLiquid
Solid particles suspended in a liquid is called a suspension
Ex Blood (blood cells suspended in plasma) Liquid dispersed throughout a solid medium is called a
gel Ex Fruit Jelly (water trapped in a solid protein matrix)
LiquidLiquid Stable blend of two liquids that donrsquot mix is called an
emulsion Ex Mayonaisse (oil droplets suspended in aqueous system)
LiquidGas or GasLiquid Gas bubbles trapped in liquid medium is called a foam
Ex Whipped cream or egg whites Liquid droplets suspended in gas are called aerosols
Ex Aromas from food carried through the air
Texture Dispersed systems will slowly separate over
time Separation can be slowed by adding emulsifiers
Emulsifiers are stabilizers used to keep immiscible substance together
Have surfactant capability (can bind to both substances in suspension)
Similar to micelles in the action of soaps
Ex Lecithin Found commonly in egg
yolks One end is highly charged
and water soluble (bonds toaqueous phase) the otheris not (bonds to non-aqueous phase)
Texture Lecithin in mayonnaise
Lecithin is the emulsifier Mayonnaise made by beating eggs with
vinegar and oil Lecithin is found in eggs ndash charged
hydrophilic end bonds well to vinegar uncharged hydrophobic end bonds to oil
Vigorous beating produces many small oil droplets maximizing surface area for lecithin to act on and produce a stable emulsion
Stabilizers like sodium phosphate or metals are added to prevent separation (chefs use metal bowls)
hydrophilic
hydrophobic
Stereochemistry in Food Many food-specific compounds have a chiral
carbon atom and thus exist as two different enantiomers (optical isomers) Optical isomers are mirror images of one another ldquoOptical activityrdquo refers to the fact that the two mirror
image isomers rotate the direction of plane-polarized light in opposite directions
Enantiomers that rotate polarized light in a clockwise direction are said to be dextrorotatory (dex-tro-rota-tory) and have a + rotational value (d +) ndash In Latin dexter means ldquoright siderdquo
Enantiomers that rotate polarized light in an anti-clockwise direction are said to be laevorotatory (lay-vo-rota-tory) and have a ndash rotational value (l -) ndash In Latin laevus means ldquoleft siderdquo
There are two systems used to provide specific names to each enantiomeric form
Stereochemistry in Food Older system used for naming sugars and amino
acids Enantiomeric forms are labeled ldquoLrdquo and ldquoDrdquo
Again Laevus for left and Dexter for right Based off a compound called glyceraldehyde
chiral carbon
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Texture Many types of dispersed systems name depends on
the physical states of the substances mixed LiquidSolid or SolidLiquid
Solid particles suspended in a liquid is called a suspension
Ex Blood (blood cells suspended in plasma) Liquid dispersed throughout a solid medium is called a
gel Ex Fruit Jelly (water trapped in a solid protein matrix)
LiquidLiquid Stable blend of two liquids that donrsquot mix is called an
emulsion Ex Mayonaisse (oil droplets suspended in aqueous system)
LiquidGas or GasLiquid Gas bubbles trapped in liquid medium is called a foam
Ex Whipped cream or egg whites Liquid droplets suspended in gas are called aerosols
Ex Aromas from food carried through the air
Texture Dispersed systems will slowly separate over
time Separation can be slowed by adding emulsifiers
Emulsifiers are stabilizers used to keep immiscible substance together
Have surfactant capability (can bind to both substances in suspension)
Similar to micelles in the action of soaps
Ex Lecithin Found commonly in egg
yolks One end is highly charged
and water soluble (bonds toaqueous phase) the otheris not (bonds to non-aqueous phase)
Texture Lecithin in mayonnaise
Lecithin is the emulsifier Mayonnaise made by beating eggs with
vinegar and oil Lecithin is found in eggs ndash charged
hydrophilic end bonds well to vinegar uncharged hydrophobic end bonds to oil
Vigorous beating produces many small oil droplets maximizing surface area for lecithin to act on and produce a stable emulsion
Stabilizers like sodium phosphate or metals are added to prevent separation (chefs use metal bowls)
hydrophilic
hydrophobic
Stereochemistry in Food Many food-specific compounds have a chiral
carbon atom and thus exist as two different enantiomers (optical isomers) Optical isomers are mirror images of one another ldquoOptical activityrdquo refers to the fact that the two mirror
image isomers rotate the direction of plane-polarized light in opposite directions
Enantiomers that rotate polarized light in a clockwise direction are said to be dextrorotatory (dex-tro-rota-tory) and have a + rotational value (d +) ndash In Latin dexter means ldquoright siderdquo
Enantiomers that rotate polarized light in an anti-clockwise direction are said to be laevorotatory (lay-vo-rota-tory) and have a ndash rotational value (l -) ndash In Latin laevus means ldquoleft siderdquo
There are two systems used to provide specific names to each enantiomeric form
Stereochemistry in Food Older system used for naming sugars and amino
acids Enantiomeric forms are labeled ldquoLrdquo and ldquoDrdquo
Again Laevus for left and Dexter for right Based off a compound called glyceraldehyde
chiral carbon
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Texture Dispersed systems will slowly separate over
time Separation can be slowed by adding emulsifiers
Emulsifiers are stabilizers used to keep immiscible substance together
Have surfactant capability (can bind to both substances in suspension)
Similar to micelles in the action of soaps
Ex Lecithin Found commonly in egg
yolks One end is highly charged
and water soluble (bonds toaqueous phase) the otheris not (bonds to non-aqueous phase)
Texture Lecithin in mayonnaise
Lecithin is the emulsifier Mayonnaise made by beating eggs with
vinegar and oil Lecithin is found in eggs ndash charged
hydrophilic end bonds well to vinegar uncharged hydrophobic end bonds to oil
Vigorous beating produces many small oil droplets maximizing surface area for lecithin to act on and produce a stable emulsion
Stabilizers like sodium phosphate or metals are added to prevent separation (chefs use metal bowls)
hydrophilic
hydrophobic
Stereochemistry in Food Many food-specific compounds have a chiral
carbon atom and thus exist as two different enantiomers (optical isomers) Optical isomers are mirror images of one another ldquoOptical activityrdquo refers to the fact that the two mirror
image isomers rotate the direction of plane-polarized light in opposite directions
Enantiomers that rotate polarized light in a clockwise direction are said to be dextrorotatory (dex-tro-rota-tory) and have a + rotational value (d +) ndash In Latin dexter means ldquoright siderdquo
Enantiomers that rotate polarized light in an anti-clockwise direction are said to be laevorotatory (lay-vo-rota-tory) and have a ndash rotational value (l -) ndash In Latin laevus means ldquoleft siderdquo
There are two systems used to provide specific names to each enantiomeric form
Stereochemistry in Food Older system used for naming sugars and amino
acids Enantiomeric forms are labeled ldquoLrdquo and ldquoDrdquo
Again Laevus for left and Dexter for right Based off a compound called glyceraldehyde
chiral carbon
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Texture Lecithin in mayonnaise
Lecithin is the emulsifier Mayonnaise made by beating eggs with
vinegar and oil Lecithin is found in eggs ndash charged
hydrophilic end bonds well to vinegar uncharged hydrophobic end bonds to oil
Vigorous beating produces many small oil droplets maximizing surface area for lecithin to act on and produce a stable emulsion
Stabilizers like sodium phosphate or metals are added to prevent separation (chefs use metal bowls)
hydrophilic
hydrophobic
Stereochemistry in Food Many food-specific compounds have a chiral
carbon atom and thus exist as two different enantiomers (optical isomers) Optical isomers are mirror images of one another ldquoOptical activityrdquo refers to the fact that the two mirror
image isomers rotate the direction of plane-polarized light in opposite directions
Enantiomers that rotate polarized light in a clockwise direction are said to be dextrorotatory (dex-tro-rota-tory) and have a + rotational value (d +) ndash In Latin dexter means ldquoright siderdquo
Enantiomers that rotate polarized light in an anti-clockwise direction are said to be laevorotatory (lay-vo-rota-tory) and have a ndash rotational value (l -) ndash In Latin laevus means ldquoleft siderdquo
There are two systems used to provide specific names to each enantiomeric form
Stereochemistry in Food Older system used for naming sugars and amino
acids Enantiomeric forms are labeled ldquoLrdquo and ldquoDrdquo
Again Laevus for left and Dexter for right Based off a compound called glyceraldehyde
chiral carbon
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Stereochemistry in Food Many food-specific compounds have a chiral
carbon atom and thus exist as two different enantiomers (optical isomers) Optical isomers are mirror images of one another ldquoOptical activityrdquo refers to the fact that the two mirror
image isomers rotate the direction of plane-polarized light in opposite directions
Enantiomers that rotate polarized light in a clockwise direction are said to be dextrorotatory (dex-tro-rota-tory) and have a + rotational value (d +) ndash In Latin dexter means ldquoright siderdquo
Enantiomers that rotate polarized light in an anti-clockwise direction are said to be laevorotatory (lay-vo-rota-tory) and have a ndash rotational value (l -) ndash In Latin laevus means ldquoleft siderdquo
There are two systems used to provide specific names to each enantiomeric form
Stereochemistry in Food Older system used for naming sugars and amino
acids Enantiomeric forms are labeled ldquoLrdquo and ldquoDrdquo
Again Laevus for left and Dexter for right Based off a compound called glyceraldehyde
chiral carbon
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Stereochemistry in Food Older system used for naming sugars and amino
acids Enantiomeric forms are labeled ldquoLrdquo and ldquoDrdquo
Again Laevus for left and Dexter for right Based off a compound called glyceraldehyde
chiral carbon
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Stereochemistry in Food When a 3D sketch of glyceraldehyde is viewed with the C=O
bond pointing away from the observer the ldquoLrdquo form will have the ndashOH group on the left the ldquoDrdquo form will have the ndashOH group on the right
Chiral sugars are named the same way by pointing the C=O group away and describing the location of the ndashOH group (ldquoLrdquo form ndashOH on left ldquoDrdquo form ndashOH on right
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Stereochemistry in Food ldquoLrdquo and ldquoDrdquo system is also used in naming
enantiomeric amino acids 19 of the 20 amino acids have a chiral carbon
The 4 substituents on this carbon are a COOH group an R group a hydrogen atom and a NH2 group
Naming follows the CORN rule Amino acid is positioned so that the C-H bond is facing
away from the observer ldquoDrdquo form has the remaining substituent groups COOH R
and NH2 arranged clockwise ldquoLrdquo form has the remaining substituent groups COOH R
and NH2 arranged anti-clockwise
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Stereochemistry in Food Ex CORN rule applied to alanine
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
- Shelf Life (10)
- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Stereochemistry in Food A more modern system exists where ldquoLrdquo and ldquoDrdquo are
replaced with ldquoRrdquo and ldquoSrdquo (R S system) Used for other compounds outside of sugars and
proteins Naming based off of a ldquorankingrdquo system of chiral carbon
substituent groups Each substituent is given a rank according to its molar mass
specifically the mass of the actual atom bound to the chiral carbon
In cases where there are two like atoms bound to the chiral carbon the mass of the next atom is used in the rank
Molecule is positioned with ldquolowest rankingrdquo substitutent pointed away from the observer remaining substituents will decrease in order of rank
If remaining substituentsrsquo ranks decrease in a clockwise direction ndash R enantiomer
If remaining substituentsrsquo ranks decrease in an anti-clockwise direction ndash S enantiomer
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
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-
Stereochemistry in Foods Ex 2-bromo butane
Substituents on the chiral carbon are CH3 C2H5 H and Br Ranks H lt CH3 lt C2H5 lt Br
Note that two substituents begin with a ldquoCrdquo atom ndash rank determined by next atom (3 H are lower mass than a C so CH3 ranks lower)
Not part of this example but count double bonds as two of that atom (Ex COOH rank determined by C then 3 O atoms as one of these O atoms is double bonded and counts as two O atoms)
chiral carbon
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
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- Shelf Life
- Shelf Life (2)
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- Color (6)
- Color (7)
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- Color (9)
- Color (10)
- Color (11)
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- Color (13)
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- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
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- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Stereochemistry in Foods
In ldquoRrdquo form remaining substituentsrsquo ranks decrease clockwise (Br C2H5 CH3)
In ldquoSrdquo form remaining substituentsrsquo ranks decrease anti-clockwise (Br C2H5 CH3)
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
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- Fats and Oils
- Shelf Life
- Shelf Life (2)
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- Color (2)
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- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-
Stereochemistry in Foods Two enantiomers of the same compound may have
different flavors R-carvone = spearmint flavor S-carvone ndash caraway seed
flavor R-limonene = orange flavor S-limonene = lemon flavor
Biosynthesis tends to be stereospecific ndash ie natural flavor compounds are 100 one enantiomer and not the other
Artifical flavors are produced as a racemic mixture (5050 mix of both enantiomers) as this is much cheaper which can affect flavor Care must be taken to ensure one
enantiomer is not toxic
- Food Chemistry
- Nutrients
- Food Groups
- Nutrients (carbohydrates)
- Nutrients (carbohydrates) (2)
- Nutrients (fats and oils)
- Nutrients (fats and oils)
- Nutrients (proteins)
- Nutrients (water and vitaminsminerals)
- Fats and Oils
- Fats and Oils (2)
- Fats and Oils (3)
- Fats and Oils (4)
- Fats and Oils (5)
- Fats and Oils (6)
- Fats and Oils (7)
- Fats and Oils
- Shelf Life
- Shelf Life (2)
- Shelf Life (3)
- Shelf Life (4)
- Shelf Life (5)
- Shelf Life (6)
- Shelf Life (7)
- Shelf Life (8)
- Shelf Life (9)
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- Shelf Life (11)
- Shelf Life
- Color
- Color (2)
- Color (3)
- Color (4)
- Color (5)
- Color (6)
- Color (7)
- Color (8)
- Color (9)
- Color (10)
- Color (11)
- Color (12)
- Color (13)
- Color (14)
- Color (15)
- Color (16)
- Color (17)
- Genetically Modified Foods
- Genetically Modified Foods (2)
- Texture
- Texture (2)
- Texture (3)
- Texture
- Stereochemistry in Food
- Stereochemistry in Food (2)
- Stereochemistry in Food (3)
- Stereochemistry in Food (4)
- Stereochemistry in Food (5)
- Stereochemistry in Food (6)
- Stereochemistry in Foods
- Stereochemistry in Foods (2)
- Stereochemistry in Foods (3)
-