Download Ch.3 Fermentation File

Chapter 3 . Fermentation
By: M.Sc. Mohammed Sabah
Book of Food Processing Technology page. 194-217
2013
Fermentation Food
 Fermentation consists of the transformation of
simple raw materials into a range of value-added
products by utilizing the phenomena of the growth
of microorganisms and their activities on various
substrates.
 Fermentation in food processing typically is the
conversion of carbohydrates to alcohols and
carbon dioxide or organic acids using yeasts,
bacteria, or a combination there of, under
anaerobic conditions. Fermentation in simple
terms is the chemical conversion of sugars into
ethanol.
1. History of Fermented Foods
 After drying, fermentation is the oldest food
preservation method. Fermentation became
popular with the dawn of civilization because it
not only preserved food but also gave it a variety
of tastes, forms, and other sensory sensations.
 Today they continue to form major sectors of the
food processing industry, including baked
products, alcoholic drinks, yoghurt, cheese and soy
products among many others.
 During food fermentations, the controlled action
of selected micro-organisms is used to alter the
texture of foods, preserve foods by production of
acids or alcohol, or to produce subtle flavours and
aromas which increase the quality and value of
raw materials.
The main advantages of fermentation as a method of
food processing are:
 the use of mild conditions of pH and temperature
which maintain (and often improve) the nutritional
properties and sensory characteristics of the food.
 the production of foods which have flavours or
textures that cannot be achieved by other
methods.
 low energy consumption due to the mild
operating conditions.
 relatively low capital and operating costs
 relatively simple technologies.
2. Theory
The main factors that control the growth and activity of
micro- organisms in food fermentations are:
• availability of carbon and nitrogen sources, and any
specific nutrients required by individual microorganisms.
• substrate pH
• moisture content
• incubation temperature
• redox potential
• stage of growth of micro-organisms
• presence of other competing micro-organisms.
The final quality and safety of the fermented product
are dependent on factors such as:
(i) Quality of the raw material
(ii) Initial level of contamination (which in turn
depends on local conditions)
(iii) Levels of hygiene and sanitation
(iv) Quality of the starter culture
(v) Conditions of fermentation (e.g. temperature)
(vi) Degree of acidity achieved.
Quality and Safety of the Fermented Product
BENEFITS OF FERMENTED FOODS
3. Types of food fermentations
Micro-organisms that produce a single main byproduct are termed homofermentative whereas those
that produce mixed products are heterofermentative.
Fermentations can be classified into those in which the
main products are organic acids and those in which
ethanol and carbon dioxide are the primary products.
4. Classification
Classified foods in 7 classes:
(1) beverages
(2) cereal products
(3) dairy products
(4) fish products
(5) fruit and vegetable Products
(6) Legumes
(7) meat products
5. MICROORGANISMS ASSOCIATED WITH FERMENTED
FOODS
Fermented foods may be produced with the use of
starter microorganisms or by the action of natural
fermentative microorganisms present in the raw
materials or production environment.
5.1 Yeast
 Yeasts are widely distributed in nature, with their
natural habitats usually being nutritionally rich and
high in carbohydrates. They are regularly associated
with plant nectars and fruits.
 Consequently, in fermentations they are frequently
used for beverages and foods based on fruit or
vegetable substrates. Yeasts are ideal agents for
fermentation of food products as they are generally
acceptable to consumers and are rarely toxic or
pathogenic.
 All strains ferment glucose and many ferment other
plant-associated carbohydrates such as sucrose,
maltose and raffinose, although none ferment
lactose. In general, yeasts do not ferment starch in
nature.
 Yeasts are used to produce ethanol, CO2, flavour
and aroma. The important reaction of yeasts can be
represented by the following equations:
C6H12O6 → 2C2H5OH + 2CO2
glucose → ethyl alcohol and carbon dioxide
5.2 Lactic acid bacteria
 Lactic acid bacteria are a group of bacteria that
predominate in many fermented foods. These
bacteria are grouped together based on a set of
common properties.
 Lactic acid bacteria are subdivided based on their
end products from glucose metabolism. Two
distinct groups known as homofermenters and
heterofermenters are identified.
 The homofermenters produce lactic acid. The
heterofermenters produce equimolar amounts of
lactate, carbon dioxide, and ethanol/acetate from
hexoses.
 Lactic acid bacteria perform an essential role in the
preservation and production of wholesome foods.
Examples of lactic acid fermentations include: a)
fermented vegetables such as: sauerkraut, pickled
cucumbers, radishes, carrots, olives, b) fermented
milks such as: yogurt, kefir, cheeses, c) fermented
breads such as sourdough breads and d) fermented
sausages.
Figure 2 Major fermentation pathways of glucose: (A) homolactic fermentation (glycolysis, EmbdenMeyerhof-Parnas pathway); (B) heterolactic fermentation (6-phosphogluconate/phosphoketolase
pathway). Selected enzymes are numbered: 1. Glucokinase; 2. fructose-1,6-diphosphate aldolase; 3.
glyceradehyde-3-phosphate dehydrogenase; 4. pyruvate kinase; 5. lactate dehydrogenase; 6.
glucose-6-phosphate dehydrogenase; 7. 6-phosphogluconate dehydrogenase; 8. phosphoketolase;
9. acetaldehyde dehydrogenase; 10. alcohol dehydrogenase.
 The benefits may arise from the growth and activity
of the lactic acid bacteria during food fermentation
or during colonisation of the gastrointestinal tract.
6. Dairy Products
6. 1- Yogurt
 Yogurt is a fermented milk product produced with
a yogurt starter culture consisting of Streptococcus
thermophilus and L. dulbrueckii subsp bulgariecus
in a 1:1 ratio. The symbiotic growth of the two
organisms results in lactic acid production at a rate
greater than that produced by either when
growing alone, as well as the production of various
metabolites.
Figure 7. Relationship between Starter Bacteria in Milk Fermentation (Celik, 2007).
Steps of Manufacturing Yogurt
4- Acidophilus milk
 Acidophilus milk is produced by the inoculation of a strain of
Lactobacillus acidophilus into sterile milk. The inoculum of 1–
2% is added. Acidophilus milk contains from 1.5 to 2.0% acid (as
lactic) and no alcohol.
5- cheese
 Cheese is commonly made from cow, ewe, goat, or buffalo
milk.
Fermented breads
1. Sourdough
Sourdough is a bread product made by a long fermentation
of dough using
naturally
occurring yeasts and lactobacilli.
In
comparison with breads made quickly with cultivated yeast, it usually
has a mildly sour taste because of the lactic acid produced by the
lactobacilli.
Fermented fruits and vegetables
1.1. Sauerkraut
 Sauerkraut is the product resulting from the natural lactic acid
fermentation of shredded fresh cabbage to which salt is added
at a concentration of 2.25–2.5%.
 The fermentation yields lactic acid
as the major product. The salt
extracts liquid from the vegetable
which serves as a substrate for
growth of lactic acid bacteria.
 Anaerobic conditions should be
maintained to prevent growth of
microorganisms that might spoil
the sauerkraut
Meat and fish products
 Fermented sausages (for example salami, pepperoni, medwurst and
bologna) are produced from a mixture of finely chopped meats, spice
mixtures, curing salts (sodium nitrite/nitrate), salt and sugar.
 The meat is filled into sausage casings, fermented and then pasteurised
at 65–68ºC for 4–8 h, dried and stored at 4–7ºC.
 In Southeast Asia, small fish, shrimp or waste fish are mixed with dry
salt and fermented by bacteria including L. mesenteroides,
Pediococcus cerevisiae and L. plantarum to produce a range of sauces
and pastes.
 Proteins in the fish are broken down by the combined action of bacterial
enzymes, acidic conditions and autolytic action of the natural fish
enzymes
Preservation is due to:
• the antimicrobial action of nitrite-spice mixtures and to a lesser
extent from added salt.
• 0.84–1.2% lactic acid from the fermentation.
• heat during pasteurization and/or smoking (and antimicrobial
components in smoke when the product is smoked).
• reduction in water activity due to salt and drying.
• low storage temperature.
Beverages
1. Kombucha Tea
Kombucha tea is made by fermenting sweetened black tea with a
flat, pancake-like culture of yeasts and bacteria called the
"Kombucha mushroom". It is not actually a mushroom, but is called
one because of the shape and color of the sac that forms on top of
the tea after it ferments.
The culture used in Kombucha tea varies, but consists of several
species of yeast and bacteria. It may include Saccharomycodes
ludwigii, Schizosaccharomyces pombe, Brettanomyces bruxellensis,
Bacterium xylinum, Bacterium gluconicum, Bacterium xylinoides,
Bacterium katogenum, Pichia fermentans, Candida stellata, and
Torula species, among others.
For the beginning it is necessary to make tea. Take a mug or a
brewing teapot, put tea into it, pour it with boiled water and leave
for brewing. While tea is brewing, it is necessary to solve sugar in
water. Be attentive and do not put sugar into the infusion with
Kombucha – it may be burned and fall ill. It is more convenient to
take a small pan, to put sugar into it and solve it in a small amount
of hot water (on a cooker is possible). As a result we have sugar
syrup of a very high density.
1
3
2
4
Make sure that the jar is not full and it still has some space for
Kombucha and air. Accurately immerse the Kombucha into the
infusion obtained (Picture 5, Picture 6).
5
6
Cover the jar with pure gauze in order that dust may not get on it and at the
same time it can breathe (Picture 5).
Put the jar with the Kombucha in a silent place out of direct sun, for
example on a kitchen cupboard or a shelf (Picture 8). Leave it for a
minimum of 1 week.
In Market