fermentation class lecture
TRANSCRIPT
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Fermentation
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Fermentation involves the action of desirable microorganisms, or
their enzymes, on food ingredients to make biochemical changes,which cause significant modification to the food.
Often lactic-acid bacteria convert the carbohydrate energy source
of food, such as lactose in milk, to lactic acid; examples are yogurt
and cheeses from milk, and pickles from fruits and vegetables.
Alternatively, yeasts, often of the Saccharomyces species, may
convert the glucose to ethanol and carbon dioxide in leavened
breads, or the sugars in grain or fruit beverages to beers and wines.
It is estimated that about one-third of all the food we consume is
fermented. World estimates for beer consumption are about 22
million gallons, and a total of 15 million tons of some one thousand
varieties of cheese are eaten annually.
What is Fermentation
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Alcoholic fermentation
Two stages:
Step 1: Glycolysis Results in the production of2 molecules of ATP
Step 2: Pyruvic acid is broken down into CO2 and alcohol
No ATP is produced in this stage
Total energy produced in both stages is 2 molecules of ATP
End products are CO2, alcohol, and 2 molecules of ATP
Used in the baking and brewing industry.
This is the process which for example yeast use. When there is a
lack of oxygen, the cells start to produce CO2 and alcohol as waste.
This is the reason why yeast is used in baking. Bread for example,
wouldn't rise without yeast, but it does rise because yeast creates CO2
which makes it rise.
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The smell that you get from baking, is from the alcohol burning
off. The reason we do not get intoxicated when eating bread
(because of the alcohol that is made from the fermentation) is
because the alcohol is burned off during baking because of high
temperatures.
LacticAcid Fermentation
Process occurs in two stages: Stage 1. Glycolysis
Stage 2. Pyruvic acidis broken down into lactic acid
Occurs in the cytoplasm
Total products are 2 molecules of lactic acid and 2 molecules ofATP
Occurs in humans during periods of prolonged physical activity
Oxygen levels become very low in the muscles involved and lactic
acid fermentation occurs
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Yogurt fermentation
Yogurt is made by fermenting milk with friendly bacteria, mainly
Lactobacillus bulgaricus and Streptococcus thermophilus. Yogurt fermentation was invented probably by accident by Balkan
tribes thousands of years ago. Yogurt remained mainly a food of
eastern Europe until the 1900s, when the biologist Mechnikov
created the theory that lactobacillus bacteria in yogurt are
responsible for the unusually long lifespan of the Bulgar people.
The milk sugar or lactose is fermented by these bacteria to lactic
acid which causes the characteristic curd to form. The acid also
restricts the growth of food poisoning bacteria. During the yogurt
fermentation some flavors are produced, which give yogurt its
characteristic flavor.
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KefirYogurt
Kefir means to froth and Yogurt in Turkish means dense or
thick.
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Kefir fermentation
Kefir is a fermented milk drink
Kefir fermentation is similar to yogurt fermentation.
Yogurt is only fermented by bacteria but kefir fermentation
involves the help of bacteria as well as yeasts.
These yeast produce some alcohol and carbon dioxide, whichgives kefir its typical fizzy aspect.
Kefir is inoculated with special kefir grains. These grains are
mixtures of bacteria and yeasts in a matrix of proteins, lipids and
carbohydrates.Kefir fermentation is done at room temperature, which makes the
process easier. On the other hand, not everyone likes the taste of
kefir.
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Considering the digestion, Kefir is easily digested than Yogurt.
As the Kefir curd size is smaller to that ofYogurt, it becomes
easier to get digested.
Another difference that can be noticed is that Kefirs yeast and
bacteria combination has more nutritional value than Yogurt. Kefir
also helps to keep the colon clean and healthy.
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What types of microorganisms cause fermentation to
occur?
The primary purpose of fermentation is to furnish
energy for metabolism and growth to
microorganisms including bacteria, yeast, and
mold.
A. Bacteria are typically one-celled organisms
that multiply by simple division and can be seenonly with a microscope; necessary for some
types of fermentation.
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B. Yeasts are any of various unicellular (single-celled)
fungi in which little or no mycelium develops and that
ordinarily reproduce by budding; they live on sugary
solutions. The dry granules of yeast that are bought at
the store become active when they become moist.
C. Molds are a fungus that grows in a tangled mass of
filaments containing cells. Fungi are not plants and
therefore do not photosynthesize. They are eukaryotic
(have a cell membrane and membrane bound
organelles) heterotrophs (obtain energy by consumingother organisms). Fungi break down their food outside of
their bodies and then consume it.
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What food and non-food products are created by
fermentation?
A. Foods that undergo fermentation include
yogurt, cheese, wine, cider, bread, sauerkraut,flavorings, candy, fruit juice, silage, and beer.
Pickling involves fermentation. Foods that are
frequently pickled include beans, onions,
cauliflower, cucumbers, tomatoes, and cabbage.
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Yeast
Yeast is a unicellular fungi.
Yeast flourish in habitats where sugar is
present e.g. flowers, fruit and bark of trees.A few are pathogenic for animals and
humans.
The most important commercially are
bakers or brewers yeast which are spp. of
Saccharomyces.
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Bread and Yeast
Leavened bread is made from a
combinations offlour, sugar, milk or water,
yeast, and sometimes butter or oil.Yeast (Sacchromyces) ferments the sugar
to ethanol and CO2.
The
CO2 causes the bread to riseproducing the characteristic texture.
The ethanol evaporates during baking.
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1. Bread is made through alcoholic fermentation. Yeasts
eat the sugar from the granulated sugar and the maltose
(disaccharide or double sugar; made up of two glucose
molecules) from the flour. ATP is created helping the
yeast to multiply. One yeast cell can consume its weight
in glucose in one hour. The yeast initially uses oxygen to
obtain energy and reproduce. As the oxygen is used upthey undergo alcoholic fermentation and produce alcohol
and carbon dioxide as by-products.
The alcohol burns off during baking, but leaves a good
flavor in the bread. When flour is mixed with water and
then kneaded, an elastic dough is created because of
gluten. Gluten is a protein found in wheat. This elastic
dough holds in the carbon dioxide forming small air
pockets or bubbles causing the bread to rise.
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Wine
Produced from the fermentation of fruit juice,usually from grapes
The grapes are crushed to form a must
For white wines, white grapes are usually used,
and the skins are removed from the must(pressing) before fermentation
For red wines, red or black grapes are used, andthe skin is allowed to remain during
fermentationFor ros wines, red grapes are used and the juice
is allowed to remain in contact with the skins just long enough for a rose or pink color to
develop
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Wine Production
Grapes are crushed and thejuice extracted(Must).
Depending on the grapes used and its treatment,
white or red wine is produced.White wine: white grapes with skin removed.
Red wine: pomace (skin, seed and pieces of
stem) is left during fermentation.Yeast used are 2 types:
Wild yeast present on grapes
Cultivated yeast (S. ellipsoideus)
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Wine Making
Before fermentation the wild yeast is killed by
SO2 (100 ppm).
S. ellipsoideus is added as a starter culture.
Large amounts of CO2 produced during
fermentation escapes through a one-way valve.
With red wine after 3-5 days of fermentationthe pomace is separated from the wine and
allowed to ferment for another week or two.
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Wine Making
During racking the wine is separated from the
yeast cells etc. and stored at a high temperature
foraging, flavour development and
clarification. The final clarification is aided by the addition of
fining agents such as casein, tannins and
bentonite clay or the wine is filtered.
The wine is bottled and left for aging.
Red wine: age for several years.
White wine: sold without much aging.
Wine is 6-14% alcohol.
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Fermented Foods
Beer
Produced by the fermentation of malted grain
Malted grain: Grain that has been allowed to
germinate, then dried in a kiln & perhaps roastedGerminating the grain causes the production of a
number of enzymes, most notably - and -
amylase
Malted grains that may be used are barley, rye, or
wheat
Unmalted grains, such as rice or corn, may also be
used
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Brewing
Brewing is the manufacture of alcohol
beverage from malted grains e.g. beer,
ale and stout.Beer making can be divided 3 basic
stages:
Wort making
Fermentation
Bottling and aging
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Wort Making
Malt is prepared from geminating barley
seeds.
Natural enzymes in the seed convert starch
to sugar (yeast cannot digest starch).
Mixed in with the malt are other grains e.g.
corn, rice and wheat.
The mixture is cooked and steeped. Theheat and enzyme convert starch to sugar.
After cooking the wort is filtered and hops
(female flower of the hop plant) is added.
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Hops
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Wort Making/Fermentation
The hops add flavour and has antimicrobial
properties.
Wort and hop is boiled for several hours toextract flavour from the hops and the
coagulated proteins are removed.
Fermentation
There are 2 types of brewing yeast
Top (S. carlsbergenis)
Bottom (S. cerevisiae)
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Fermentation/Bottling
Yeast is added to the wort and
fermented (6-23 C) for 5-14 days.
After this the beer is removed to largetanks and stored at a lower temperature
for several days to weeks.
Beer is taken from the storage tank andbottled.
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Beer Making
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What are some advantages and disadvantages of
fermentation in food processing?
A. Advantages include:
1. Fermentation can increase the shelf life of foods by
inhibiting the enzymatic deterioration of plant tissues.
2. Fermentation improves the dough handlingcharacteristics of bread by softening the gluten because
the gluten proteins are hydrated. This allows the dough to
be handled easier, especially by machines.
3. It can enhance the texture, flavor and odor of foods. For
example, the compound diacetyl is produced by variouslactic acid bacteria during dairy fermentations (i.e.
cottage cheese, sour cream, buttermilk). This compound is
responsible for the buttery aroma and taste typically
associated with these products.
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4. Fermentation helps food to be stored safely.
5. Fermentation allows humans to enjoy their favorite foods
in a different way by creating a variety of flavors, textures,
color, and appearance of some foods.
6. Fermentation is also used to create new energy sources
such as ethanol.
7. The vitamin content of some foods can be increased.
8. Digestibility can be improved.
9. The toxicity of some foods (particularly oriental) may be
decreased.
10. Some scientists believe that particular types of
fermented milk products (i.e. acidophilus milk, yogurt) havea therapeutic value and can be beneficial in cases of
alimentary disorders (i.e. constipation, diarrhea, etc.) and
may even preclude the development and outgrowth of
harmful bacteria.
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What factors can affect the fermentation process?
A. Fermentation time determines how long the yeast has to
act on the sugars. As time passes the rate of fermentation
decreases, but never stops under favorable conditions.
B. Yeast cells can tolerate a pH of4.08.5 with the optimum
pH between 4.0 and 6.0. Before fermentation begins in
bread dough, the pH is around 5.5 5.8. As fermentation
begins the pH drops to around 5.0. This is caused by the
production of organic acids including carbonic acid (carbondioxide dissolved in water; H2CO3 ). Carbonic acid is more
acidic than the dough. Flour and milk act as buffers to help
maintain the pH level. Calcium carbonate is a common
additive that bakeries use to buffer the pH.
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C. The presence of air affects fermentation and is
probably the most critical factor in producing somefood products. Since fermentation is anaerobic, the
presence of air will allow for yeast/mold growth and
result in softening, off flavors and darkening of the
product.
D. Optimum fermentation occurs at 75-85F for
yeast. The higher the temperature, the faster
fermentation will occur, but the flavor can be inferior
and the product will darken readily. Scientistsestimate that for every one degree increase in
temperature that fermentation of yeast will increase
three to five percent.
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E. The presence of salts affects the fermentation
process. The salt withdraws water and nutrients from
vegetative tissue in order to enable lacticmicroorganisms to grow. It also inhibits the growth of
undesirable microorganisms and delays enzymatic
spoilage.
The proper concentration of salt (2.5% for sauerkraut)favors lactics, while low salt results in softening of the
tissue because not enough water is pulled form the
tissues. High salt (over 3.5% for sauerkraut) inhibits all
lactics, including the desirable ones, slows anaerobiosis,
and results in undesirable yeast growth. Also, high saltconcentration favors lactic microorganisms that produce
only lactic acid, resulting in a rather bland product.
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