components of food chemistry project 2005-2006. carbohydrates chemistry and food
TRANSCRIPT
Components of Food
Chemistry Project 2005-2006
Carbohydrates
Chemistry and Food
What is Carbohydrates ?
Compounds composed of carbon and water General formula CxH2yOy
H:O = 2 : 1 Divided into 3 types ---Monosaccharides ---Disaccharides ---Polysaccharides
Monosaccharides
Eg.---Glucose Eg.---Fructose Basic unit of carbohydrates Sweet in taste, soluble in
water General formula C6H12O6
Disaccharides Formed from 2 monosaccharides 2C6H12O6 -----C12H22O11 + H2O Condensation
SucroseMaltose
Polysaccharides Condensation polymer of
monosaccharides nC6H12O6--(C6H10O5)n + n(H2O) Condensation Example: ---Starch ---Cellulose
Open Chain and Ring Structures of Glucose and Fructose
Glycosidic Linkage in Carbohydrates Bond formed between 2
monosaccharides Condensation---2 OH group Removal of H2O
Hydrolysis of Sucrose
Add water 2 simple sugars Dilute mineral acids
Hydrolysis of starch (1) With enzymes To maltose
Hydrolysis of Starch (2) Boiled with dilute H2SO4
To glucose (C6H10O5)n + nH2O-- nC6H12O6
Reducing and Non-reducing Sugars Reduces basic solution of Cu2+(aq) or Ag+
(aq)
Sugar converted to acid Aldehyde group Keto group
Fehling’s test
Reducing sugar and Non-reducing sugar
Reducing sugar and Non-reducing sugar
Reducing sugar and Non-reducing sugar
Proteins
Physical properties of proteins
Large Molecular mass ,typically several thousands. eg. hemoglobin :64 500 viral proteins :40 000 000
Not truly soluble on water,but form colloidal suspension
Constituent element: C,H,O,N may contain S and P
Limitless type of protein e.g. E.coli :800 types human:10 000 types
Vary form species to species
Therefore it determines the characteristics of a species
Rarely stored in organisms except in eggs or seeds.
Structure of amino acidsStructure of amino acids A group of over a hundred members
The commonest are the 20 essential ones,which cannot be synthesized by our bodies.While the rest are non-essential,and can be synthesized from the essential ones.
Zwitterions formationZwitterions formationBasic amino group : -NH2
Acidic carboxyl group : -COOH
Neutral Amino Acid:
no of amino group = no of carboxyl group
Basic Amino Acid:
no of amino group > no of carboxyl group
Acidic Amino Acid:
no of amino group < no of carboxyl group
Dipolar : with both positive and negative pole
Form zwitterions
Soluble in water but not in organic solvent
Non-volatile, crystalline organic compound with high melting point
Amphoteric : with both acidic and alkaline properties
Buffer
Biological significance : Constant Ph for enzymatic reaction
Polypeptide FormationPolypeptide FormationAmino acid (condensation)dipeptidepolypeptide
Structure of polypeptideStructure of polypeptide
Three dimension
Four types of bonding:
a) disulphide bond
b) hydrogen bond
c) hydrophobic interaction
d) ionic bond (broken by alternation in pH)
Level of proteinsLevel of proteins
DenaturationDenaturation
Change in shape but not the sequence
Factors:
- Heat
- Acid
- Alkali
- high electropositive eg.Ag+ Hg +
- high electronegative eg. CN-
- organic solvent
- Mechanical force
Function of proteinsFunction of proteins
1.cytoskeleton : cytoplasm consists of a network of fibrous
proteins
2. Membrane protein
3. Raw material for growth
4. Formation of enzymes, hormones, antibodies
5. Fibrous proteins for support and protection
6. Osmotic balance and buffering
7. Energy source
Source of proteinsSource of proteins
Egg
Milk
Daily products
Soya bean
meat
fish
etc…..
Site for protein digestionSite for protein digestion
Stomach & duodenum
Ileum
peptide
protein
Protease in intestinal juice
Protease in gastric juice and pancreatic juice
Amino Acid
Absorption of amino acidsAbsorption of amino acids
Amino acids
Capillaries in villi of small intestine
Liver
DeaminationDeamination
carbohydratesH2N-C-COOH
H
H
NH2
Urea Kidney for excretion
Deficient diseaseDeficient disease
Kwashiorkor
Symptoms of Kwashiorkor:
a) Inflammation of skin
b) Anaemia
c) Swelling of abdomen
Test for ProteinsTest for Proteins
1) Protein Turns Yellow Albustix paper green
2) Biuret test:
Protein + NaOH + CuSO4 purple colouration
(blue)
IdentificationIdentification
Paper chomatography
2 dimensioned 3 dimenstioned
Fats and Oils!!!
Foods containing Fat and Oils:
What are fats and oils?
Fats and Oils are different lipids.
Lipids are rather diverse class of organic
compounds of organic compounds that include
triglycerides, phospholipids, steriods, etc.
insoluble in water, soluble in organic solvents.
They are mainly composed of C, H, O but with a
very low proportion of oxygen in the molecules.
Structure of fats and oils:
Most natural fats and oils are mixed glycerides.
Glycerides are esters formed from propane-1,2,3-triol
(glycerol) and a mixture of different long chain
carboxylic acids.
The carboxylic acids(fatty acids) making up fats and
oils are usually unbranched, having 14 to 18 carbons.
There are three ester groups per glycerol and the three
R groups are usually different, fats and oils are often
called triglycerides.
Glycerol
A fatty acid
Triglycerides
Synthesis of Triglycerides
Microscopic views of fat cells
A more colourful one
Animal fats and Vegetable oils:
Fats and Oils are found in animals and plants.
Animal fats, such as lard and butter, are composed of glycerides rich in heavy chain, saturated fatty acids, Therefore they are solids at room temperatures.
Vegetable oils are liquids because of their high content of glycerides composed of light chain unsaturated fatty acids.
Hydrolytic and Oxidative Rancidity
Fats and Oils develop an unpleasant smell if they
are kept for too long.
They are liable to spoilage that produces an ‘off’
odour and a flavour described as rancidity.
Rancidity :
->(1) Hydrolytic (2) Oxidative
->Both of which release foul smelling aldehydes
and carboxylic acids.
Hydrolytic rancidity Presence of moisture in oils, which hydrolyzes the glyceride
molecules into propane-1,2,3-triol and free carboxylic acids.
This reaction is speeded up in the presence of certain
micro-organisms or in the presence of some enzymes.
Over a period of time, more molecules of carboxylic
acids are liberated which may be volatile and have
extremely unpleasant odours and flavours.
At room temperature, hydrolysis proceeds rapidly so that butter soon turns
rancid.
So, to duel with, butter is usually covered and refrigerated.
Oxidative Rancidity Oxidative spoilage occurs when fats/oils are exposed to
air and undergo oxidation.
It results in the production of flavours such as ‘tallowy’,
A taste of fatty according to “yahoo dictionary”.
Fats and oils with a high degree of unsaturation are
more susceptible to oxidation.
The oxidation has a free radical mechanism and is
accelerated by trace metals, light and free radical
initiators.
Autoxidation
C
H
H
C
H
C
H
C
H
H
O2 in the air
AutoxidationC
H
C
H
C
O
C
H
H
H
OH
segment of carboxylic acid in fat/oil hydroperoxide
Hydroperoxide
It is flavourless and odourless
It easily decomposes to form highly reactive
hydroperoxide free radicals
HydroperoxideHydroperoxide
free radical
cleavage of
double bonds and carboxylic acidsAldehydes,ketones
Autoxidation
Can be contolled, But not be eliminated
Can be slow down by antioxidants. Examples :
butylated hydroxyanisole (BHA)
butylated hydroxytoluene (BHT)
carotene (Pro-Vitamin A)
Vitamin E
Hydrolysis of Fats and oils
Hydrolysis is a chemical process in which a molecule is
cleaved into two parts by the addition of a molecule of
water.
Fats can be hydrolysed into carboxylic acids and
glycerol in an alkaline medium (NaOH).
It is a reversible reaction.
Saponification
Hardening of unsaturated fat An unsaturated fat is a fat in which there is one or
more double bond between carbon atoms of the
fatty acid chain.
Such fat molecules are monounsaturated if each
contains one double bond, and polyunsaturated if
each contain more than one.
Unsaturated fat cannot pack together closely,
because of their bent structure. As a result,
unsaturated oils exist as a liquid at room
temperature.
Saturation of fatty acid
Hydrogenation Hydrogenation is a chemical reaction which can convert an
oil to a semisolid fat by adding hydrogen to some of the
carboxylic acid C=C double bond , thus decreasing the
degree of unsaturation.
As a result , they can pack together closer and has a
higher melting point .
It is an important reaction to produce margarine.
Soft spread margarine are prepared by the catalytic partial
hydrogenation of vegetable oil .
Catalytic HydrogenationMargarine: An unsaturated fats
Solid forms of vegetable oil
Widely used as a substitute for butter
It is healthier than butter. (Why?)Use your brain to think…
Examples:
Corn oil
Soy bean oil
Cottonseed oil
Iodine value: Iodine value is used to measure the degree of
unsaturation in fats and oils.
It is determined by reacting fats or oils with excess
iodine which adds on across the double bonds in the
carboxylic acid side chains .
The degree of unsaturation is defined as the number of
grams of iodine needed to react with 100 grams of
fats/oils.
The greater the value is , the greater the degree of
unsaturation in the fat or oil.
Energy Source The energy yield of lipids is more than twice those of
carbohydrates and proteins, as shown in the below table.
On average, around 20-30% of the daily energy requirement of the human body comes from oxidation of lipids
Approximate amount of energy released on complete oxidation(kg g-1)
Carbohydrates 17Proteins 17Lipids 38
Energy Reserve
They provide much more energy per
gramme than carbohydrates and
proteins.
They are insoluble in water so that they
do not diffuse out of the cells and do not
upset the osmotic balance of the cells.
They can be stored in the animal body
in almost unlimited amount.
Triglycerides are common energy reserve in the adipose tissue of animals. They are an excellent storage form of energy because of the followings:
Component of cell membrane
The cell membrane is formed by two layers (bilayers) of
phospholipids, with the lipophilic hydrocarbon ends facing each
other and the hydrophilic phosphate ends pointing outward to
the aqueous environment.
Cholesterol in the cell membrane helps to limit the leakage of
small molecules, and hold the hydrocarbon chains of the
phospholipids together but not changing them into a solid form.
Regulatory components
Cholesterol is also the precursor for the synthesis of
steroid hormones. Some of them are sex hormones
that stimulate the development and maintenance of
secondary sexual characteristics.
Vitamin D, which regulates the absorption of calcium
inside the intestine, is derived from cholesterol.
Component of digestive juice
Bile salts are made in the liver with cholesterol as a raw
materials. They emulsify dietary lipids into small oil
droplets which increase the surface area for the
enzymes to work.
Heat insulation
Being a poor heat conductor, fats effectively reduce heat
loss from the bodies of many animals, such as human
beings, polar bears and penguins.
Protection Fats, being soft, light and
shock-absorbent, protect many
internal organs such as the
kidneys and the eyeball from
the mechanical injury by
cushioning them.
Cell Membrance
Credits
Ngo Yu Hin Chung Man Chuen Fung Ho On Yim Pui Kin Yeung Sheung Yai Chan Kai Hung