Introduction of Fermented food
Fermented foods are an extremely important part of human
diet and worldwide may contribute to as much as one
third of human diet. Different types of fermented food is
used in butter, cheese, bread, fermented vegetables,
fermented meats etc.
The scope of food fermentation ranged from producing
alcoholic beverages, fermented milk and vegetable
products to genetically engineered super bugs to carry out
efficient fermentation to treatment and utilization of waste
and overall producing nutritious and safe products with
Fermented foods are those food produced by
modification of raw material of either animal or
vegetable origin by the activities of micro
organisms. Bacteria , yeast and moulds can be used
to produce a diverse range of products that differ in
flavor, texture and stability from the original raw
Fermented foods are those foods which are subjected
to action of microorganisms or enzymes to get
desirable biochemical changes and cause
significant modification to food.
Concept of fermentation
In biochemical sense the term fermentation refers to the
metabolic process in which organic compounds(particularly
carbohydrates) are broken down to release energy without
the involvement of terminal electron acceptor such as
oxygen. Partial oxidation of the substrate occurs so that only
relatively small amount of ATP energy is released compared
with the energy generated if a terminal electron acceptor is
involved. Partial oxidation of a carbohydrate can give rise to
a variety of organic compounds. The compounds produced
by microorganisms vary from organism to organism and are
produced via different metabolic pathways. The term
fermentation can also be applied to any industrial process
Produces a material that is useful to humans and if the
process depends on the activity of one or more
microorganisms. These processes, known as industrial
fermentations, are usually carried out on large scale and
in vessels in which organism are normally grown in
liquid media. Some industrial fermentations in
biochemical sense but the majority are aerobic
processes in which the microorganisms use oxygen and
metabolize carbohydrates completely.
Benefits of fermented foods : Fermented foods are an
extremely valuable addition to human diet for variety of
Benefits of fermented foods
Increase in variety: Fermented foods increase the
variety of foods that are available, adding to our diet a
group of highly nutritious products with unique
characteristics. There are, for example, about 1000
different types of cheeses.
Use as ingredients: Fermented foods form important
ingredients for a wide variety of dishes and are often
used to impact special flavors, e.g pepperoni in pizzas,
yogurts in curries, cheeses in a whole range of dishes,
including soups, and soy sauce in stir fry dishes.
Improvement in nutritional quality: The fermentation
process may improve the nutritional quality of raw
material. Here are some examples:
Tape fermentation double the protein content of cassava
and increases the level of essential amino acids.
The presence of yeasts in fermented food will increase
the vitamin B content.
Anti nutritional factors such as phytase, glucosinolates
and lectins may be removed by fermentation process.
Fermentation may produce an increase in the
availability of minerals.
Preservation: Fermentation often preserves a raw
material, improving safety with regard to food borne
pathogens and increasing shelf life; compare the shelf
of raw milk(only a few days) with the shelf life of
yoghurt (several weeks).
Health benefits : Some fermented foods are said to
have definite health benefits although the scientific
evidences for this is limited. Reports suggested that
fermented milk products such as yoghurt can reduce
serum cholesterol levels and help avoid cancers,
particularly those associated with the colon. Bio
yoghurts (AB and ABT yoghurts) are said to have a
restorative effects on the gut micro flora, assisting
recovery of a normal balanced flora after oral antibiotic
Improve digestibility: Some fermented food are most
easily digested than the original raw material. People
who can not digest lactose properly (show lactose in
tolerance) can often consume some types of fermented
yoghurts) without harmful effects. Lactose in tolerance is
due to the absence of enzyme galactosidase in digestive
juices, which converts lactose to glucose and glactose.
Ingestion of dairy products leaves unabsorbed lactose in
gut which is fermented by normal gut flora giving
flatulence, abdominal pain and dirrhoea. The
fermentation of milk converts the harmful lactose to
more easily digested lactate, and theβ galactosidase in
liver starter culture organisms appears to assist in the
digestion of any residual lactose. Legume, e.g
soyabean, contain oligosaccharides such as stachyose
which are fermented in the gut to give gas and the
associated socially embarrassing flatus.
The oligosaccharides are broken down to readily
digestible monosaccharides and disaccharides during
mould fermentations of legumes, thus removing the
Detoxification of raw materials: The fermentation
process may remove toxic chemicals present in the raw
material. Cassava fermentation for example, removes a
cynogenic (cyanide producing) glycoside; cassava is
toxic if eaten raw.
Table 1 History and origins of some fermented foods
Food Approximate year
China, Korea, Japan
North Africa, Europe
North Africa, China
Southeast Asia, North Africa
Table 2 Worldwide production of some fermented foods
Food Quantity (t) Beverage Quantity (hl)
Table 3 Individual consumption of some fermented foods: average per
person per year
Soy sauce (I)
Microflora in fermented foods: By tradition, lactic
acid bacteria are the commonly used
microorganism for preservation of foods. Their
importance is associated mainly with their safe
metabolic activity while growing in food utilizing
available sugar for the production of organic acids
and other metabolites. Their common occurrence in
the foods and feeds coupled with their long lived
use contributes to their natural acceptance as
GRAS (Generally regarded as safe) for human
There are many kinds of fermented foods in which the
dominating processes and end products are contributed
by a mixture of endogenous enzymes and other
microorganisms like yeast and mould. Very often, a
mixed culture originating from the native micro flora of
the raw materials is in action in most of the food
fermentation processes. However, in an industrial scale
a particular defined starter culture, which has been
developed under controlled conditions, is first
preference so that the qualities of finished product
could be consistently maintained day after day.
Modern methods of gene technology makes it possible
for the microbiologist to design and develop starter
cultures with specific qualities. Many microbiologists
studies deal with identification of organisms isolated
from various fermented foods. Lactic acid bacteria
isolated from tomatoes that are naturally fermented
under partial anaerobic conditions. These are
Leuonostoc mesenteroides, Lactobacillus brevis and
In Asia mainly moulds of the genera Aspergillus,
Mucor, Actinomucor. Amyomyces, Neurospora and
Monascus are used in the manufacture of fermented
In Europe, mould ripened foods are primarily cheese and
meats, usually using a Penicillium species. Gari made
by fermenting cassava slurry was found to contain
Bacillus, Aspergillus and Penicillium spp. as
Lactic acid bacteria:
Major group of Fermentative organisms.
This group is comprised of 11 genera of gram-positive
○ Carnobacterium, Oenococcus, Enterococcus,
Pediococcus, Lactococcus, Streptococcus,
Lactobacillus, Vagococcus, Lactosphaera,
Weissells and Lecconostoc
Related to this group are genera such as Aerococcus,
Microbacterium, and Propionbacterium.
While this is a loosely defined group with no precise
boundaries all members share the property of producing
lactic acid from hexoses.
As fermenting organisms, they lack functional heme-
linked electron transport systems or cytochromes, they
do not have a functional Krebs cycle.
Energy is obtained by substrate-level phosphorylation
while oxidising carbohydrates.
The lactic acid bacteria can be divided into two groups
based on the end products of glucose metabolism.
Those that produce lactic acid as the major or sole
product of glucose fermentation are designated
Those that produce equal amounts of lactic acid,
ethanol and CO2 are termed heterofermentative.
The homolactics are able to extract about twice as much
energy from a given quantity of glucose as the
All members of Pediococcus, Lactococcus,
Streptococcus, Vagococcus, along with some
lactobacilli are homofermenters.
Carnobacterium, Oenococcus, Enterococcus,
Lactosphaera, Weissells and Lecconostoc and some
Lactobacilli are heterofermenters
The heterolactics are more important than the
homolactics in producing flavour and aroma
components such as acetylaldehyde and diacetyl.
Lactic Acid Bacteria – Growth:
The lactic acid bacteria are mesophiles:
they generally grow over a temperature range of
about 10 to 40oC,
an optimum between 25 and 35oC.
Some can grow below 5 and as high as 4oC.
Most can grow in the pH range from 4 to 8. Though
some as low as 3.2 and as high as 9.6.
Starter Cultures :
Traditionally the fermenting organisms came from the
natural micro flora or a portion of the previous
In many cases the natural micro flora is either
inefficient, uncontrollable, and unpredictable, or is
destroyed during preparation of the sample prior to
fermentation (e.g. pasteurization).
A starter culture can provide particular characteristics in
a more controlled and predictable fermentation.
Lactic starters always include bacteria that convert
sugars to lactic acid, usually:
Lactococcus lactis subsp. lactis,
Lactococcus lactis subsp. cremoris or
Lactococccus lactis subsp. lactis biovar
Where flavour and aroma compounds such as diacetyl
are desired the lactic acid starter will include
heterofermentative organisms such as:
Leuconostoc citrovorum or
The primary function of lactic starters is the production
of lactic acid from sugars
Other functions of starter cultures may include the
○ flavour, aroma, and alcohol production
○ proteolytic and lipolytic activities
○ inhibition of undesirable organisms
A good starter CULTURE will:
Convert most of the sugars to lactic acid
Increase the lactic acid concentration to 0.8 to 1.2 %
Drop the pH to between 4.3 to 4.5
Food scientists frequently use the ability of bacterial cells to
grow and form colonies on solid media to:
isolate bacteria from foods,
to determine what types and
how many bacteria are present.
A single bacterial colony
A single bacterial colony
The streak plate technique :
Bacteria are “streaked "over the surface of an agar plate
so as to obtain single colonies.
Obtaining single colonies is important as it enables;
colour of the individual colonies to be examined.
It can also highlight the presence of
Nutritional value of fermented
There is a significant increase in the soluble fraction of
food during fermentation. The quantity and quality of
food proteins is expressed by biological value, and
often the content of water soluble vitamins is increased,
while the anti nutritional factors show a decline during
fermentation. Fermentation also results in a lower
proportion of dry matter in food and concentrations of
vitamins, minerals and protein appear to increase when
measured on dry weight basis.
Single as well as mixed culture fermentation of pearl
millet flour with yeast and lactobacilli significantly
increased the total amount of soluble sugars, reducing
and non reducing sugar content of anti nutritional
factors to a safe level in comparison
With other methods of processing.
Proteins: The protein efficiency ratio (PER) of wheat
increases on fermentation, partly due to increase in
availability of lysine. A mixture of wheat and soyabeans
in equal amounts provides and improved pattern of
amino acids. The fermentation process raises the PER
value of mixture to a level which is comparable to that
Fermentation may not increase the content of protein and
amino acids unless ammonia or urea is added as
nitrogen source to the fermentation media. The relative
nutritional value (RNV) of maize increased from 65%
to 81% when it is germinated, and
fermentation of flour made of the germinated maize gives
a further increase in RNV to 87 % .
Vitamins: During fermentation certain microorganisms
produce vitamins at higher rate than others do.
Fermented milk products in general show an increase in
folic acid content and slight decrease in vitamin B12
while other B vitamins are affected only slightly in
comparison to raw milk. The levels of vitamin b12,
riboflavin and folacin are increased by lactic acid
fermentation of maize flour, while the level of
pyridoxin is decreased.
Minerals: The mineral content is not affected by
fermentation unless some salts are added to the product
during fermentation or by leaching when liquid portion
is separated from the fermented food. Some times,
when fermentation is carried out in metal containers
some minerals are solublised by the fermented product,
which may cause an increase in mineral content.
Phytate content in bread is lowered when the amount of
yeast or the fermentation time is raised.
Definition: In simple term cheese is the curd of milk
separated from the whey and pressed in to solid mass. It
is defined as a product made from the curd obtained
from the milk by coagulating the casein with the help of
rennet or similar enzymes in the presence of lactic acid
produced by added or adventious microorganisms, from
which part of moisture has been removed by cutting,
cooking and/ or pressing, which has been shaped in and
then ripened by holding it for sometime at suitable
temperatures and humilities.
Types of cheeses: The classification of cheese is based
on a number of factors like raw material, type of
consistency, appearance(interior and exterior), fat
content, moisture content
and ripening methods. However, the most commonly used
criteria are the moisture content of the finished product and
mode of ripening.
i) Types based on moisture content:
Very hard(maximum 34% moisture)
Hard (maximum 39% moisture)
Semi hard/ semi soft (39-50% moisture)
Soft (50-80% moisture)
ii) Type based on mode of ripening
Bacteria ripened: Ripening is brought about by different
bacteria like Lactococci, Lactobacilli, Pedococci,
Propionibacteria, and brevibacteria etc.
Mold ripened: Ripening is brought about by mold
species like Penicillium.
Unripened: Ripening is not done.
Basic processes involved in cheese production : The
cheese production involves the following three main
A. Coagulum formation
B. Separation of curd from whey, and
C. Ripening of cheese
Coagulum Formation: Milk coagulation occurs due to
Inoculation with bacterial cultures e.g. Streptococcus
lactis or S. cremoris(for incubating at 31 C) or S.
thermophilus combined with Lactobacillus lactis, L.
bulgaricus or L. helveticus (for incubation at 50C)
results in lactose degradation to produce lactic acid,
which lowers the pH to about 4.6.
Incubation with rennet cleaves k casein into para casein
and caseino macro peptides. This cleavage occurs at
specific peptide bonds between phenylalanine at
position105 and meithonine at position 106 and leads to
coagulation of α andβ caseins and k casein hydrolysis
k- casein stabilizes the colloidal nature of milk. The N
Region of k- casein is hydrophobic and it associates with
the lipophilic regions of α andβ casein, which are
insoluble. The C- terminal region of k-casein is
hydrophilic and associates with water molecules. Thus
an intact k casein molecule keeps the insoluble α andβ
casein in suspension and prevents their coagulation.
Hydrolysis of k casein by rennet separates its
hydrophobic and hydrophilic regions and thereby ,
eliminates its protective influence. As a result the α and
β caseins plus the k casein hydrolysis products
participate and form the coagulum. Calcium is essential
for coagulation, and the process is very temperature
Separation of curd: The coagulum is heated to 37 C and
cooled. This eliminates rennet activity and separates, to some
extent, the watery fluid called whey. The curd is separated
from whey, salted, and mixed with proteases and/ or lipases;
alternatively, bricks of cheese may be inoculated with
specific strains of fungi, e.g. Penicillium camembertii, etc.
The bricks are pressed to remove excess moisture to enable
Ripening : Ripening procedures will vary with the type of
cheese produced. The cheese bricks are inoculated with
specific strain of fungi (P. roquefortii and P. camembertii)
for the development of appropriate flavours through protease
and lipase activities. Alternatively , protease and lipase may
be used for this purpose
Protease from B. amyloliquefaciens are used to
enhance flavors in cheddar cheese.
Protease hydrolyze proteins to produce peptides of
variable sizes. Peptides having terminal acidic amino
acids residues produce meaty appetizing flavors. But
hydrophobic amino acids residues located non
terminally produce bitter flavors; the flavors are
strongest in medium sized peptides are absent in longer
peptides and they decrease with decrease in peptide
size. Therefore, the kind and degree of flavor in cheese
can be controlled by regulating protein hydrolysis.
Common Cheese Making Steps
Cutting and Cooking
Milling and Salting Forming and Pressing Curing or Ripening
Draining, Matting and Washing
Starter and Rennet Addition
Coagulation- Change from a fluid to a thickened mass;
Whey- The watery part of milk that separates after the
milk sours and thickens.
Brine- Water strongly saturated with salt.
Rennin- A stomach enzyme that coagulates casein and is
used to commercially curdle milk in the making of cheese.
But now microbial rennin are used.
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