is the intentional use of fermentation by microorganisms to produce products
helpful to humans in large quantities or numbers.The organisms used for
fermentation can be yeasts, molds, algae, animal cells, or plant cells. The
speed of fermentation depends on the concentration of microorganisms, cells,
cellular elements, and enzymes. Factors such as temperature and pH also affect
Nearly all commercially
created enzymes are created by fermentation with genetically changed microbes.
In some cases, production of biomass itself is the objective, as within the
case of yeast and carboxylic acid microorganism starter cultures for
fermentations will be divided into four types:
Production of biomass (viable cellular
Production of extracellular metabolites
Production of intracellular elements (enzymes and different proteins)
Transformation of substrate (in that the
reworked substrate is itself the product)
In most industrial
fermentations, the organisms or eukaroyotic cells are submerged in a liquid
medium; in others, like the fermentation of cocoa beans, cherries, and miso,
fermentation takes place on the dampish surface of the medium.
The naturally occurring phenomenon of fermentation precedes human history
and we have been exploiting this process since time immemorial. Research tells
us that the earliest evidence of alcoholic drink, made from fruit, rice and
honey, dates back to 7000 to 6000 BC, in the Neolithic Chinese village of
Jiahu. Winemaking dates from 6000 BC, in Georgia (Caucasus area).
Seven-thousand-year-old jars containing the remnants of wine have been
displayed at the University of Pennsylvania, which were excavated in the Zagros
Mountains in Iran. Evidences reveal that many people were fermenting alcoholic
drinks in Babylon 3000s BC, ancient Egypt 3150s BC, pre-Hispanic Mexico 2000s
BC and Sudan 1500s BC.
Louis Pasteur, the French chemist was instrumental in the development of
the field of zymology (study of biochemical process of fermentation and its
applications), when in 1856 he exploited yeast for fermentation. While studying
the fermentation of sugar to alcohol using yeast, Pasteur inferred that the
fermentation was catalyzed by a vital force called “ferments”, present within
the yeast cells. These “ferments” were thought to function only inside living
organisms. “Alcoholic fermentation is an act correlated with the life and
organization of the yeast cells, not with the death or putrefaction of the
cells”, he wrote.
Nevertheless, it was known that yeast extracts can ferment sugar even in
the absence of living yeast cells. While studying this process in 1897, Eduard
Buchner of Humboldt University of Berlin, Germany, found that sugar was
fermented even when there were no living yeast cells in the mixture, by a yeast
secreted enzyme complex that he termed ‘zymase’. In 1907 he received the Nobel
Prize in Chemistry for his research and discovery of “cell-free fermentation”.
The Biochemical Process
organisms need energy to grow. This energy comes from the reduction of
adenosine triphosphate (ATP) into adenosine diphosphate (ADP) and results in
the release of energy and a phosphate group. In this way ATP serves as a
storage molecule of energy which can be used by the cell.
Cells get their ATP
from the controlled chemical breakdown of glucose to form two molecules of
pyruvate. This process requires two molecules of ATP but results in the release
of four molecules or a net gain of two molecules of ATP. This process is
referred to as glycolysis.
Once pyruvate is
formed, it can be processed in several different ways. Mammalian cells usually
process pyruvate by putting it into the tricarboxylic or Kreb’s cycle. In the
presence of oxygen, oxidative phosphorylation produces more ATP from the
byproducts of the Kreb’s cycle reactions. This is referred to as aerobic
However, when oxygen is
limiting, other processes must be used in order to deal with pyruvate. This is
done through anaerobic respiration or fermentation and involves the breakdown
of pyruvate into simpler compounds. Two of the most important fermentation processes
which are used on an industrial scale are ethanol or lactic acid fermentation.
A fermenter is a large
vessel/tank that provides an environment for fermentation to take place. It
provides the appropriate conditions like, temperature, pH, humidity and so on,
for the micro organisms to convert the provided substrate to the desired
Fermenters are employed
in order to conduct the production many fermented products on a large scale in
the food industry among many other indisutries. Given below is a list of some
of most commonly used fermenters, which are used specifically for the type of
reaction to occur.
Stirred Tank Fermenter
fermentations received prominence during 1940’s namely for the production of
life saving antibiotics . Stirred tank reactor’s have the
following functions: homogenization, suspension of solids, dispersion of
gas-liquid mixtures, aeration of liquid and heat exchange. The stirred tank
reactor is provided with a baffle and a rotating stirrer is attached either at
the top or at the bottom of the bioreactor.
typical decision variables are: type, size, location and the number of
impellers; sparger size and location. These determine the hydrodynamic pattern
in the reactor, which in turn influence mixing times, mass and heat transfer
coefficients, shear rates etc. The conventional fermentation is carried out in
a batch mode. Since stirred tank reactors are commonly used for batch processes
with slight modifications, these reactors are simple in design and easier to
of the industrial bioprocesses even today are being carried out in batch
reactors though significant developments have taken place in the recent years
in reactor design, the industry, still prefers stirred tanks because in case of
contamination or any other substandard product formation the loss is minimal.
The batch stirred tanks generally suffer due to their low volumetric
productivity. The downtimes are quite large and unsteady state fermentation
imposes stress to the microbial cultures due to nutritional limitations. The
fed batch mode adopted in the recent years eliminates this limitation. The stirred
tank reactor’s offer excellent mixing and reasonably good mass transfer rates.
The cost of operation is lower and the reactors can be used with a variety of
microbial species. Since stirred tank reactor is commonly used in chemical
industry the mixing concepts are well developed. Stirred tank reactor with
immobilized cells is not favoured generally due to attrition problems; however
by separating the zone of mixing from the zone of cell culturing one can
successfully operate the system.
Airlift fermenter (ALF)
is generally classified as pneumatic reactors without any mechanical stirring
arrangements for mixing. The turbulence caused by the fluid flow ensures
adequate mixing of the liquid. The draft tube is provided in the central
section of the reactor. The introduction of the fluid (air/liquid) causes
upward motion and results in circulatory flow in the entire reactor. The
air/liquid velocities will be low and hence the energy consumption is also low.
ALFs can be used for both free and immobilized cells. There are very few
reports on ALFs for metabolite production. The advantages of Airlift reactors
are the elimination of attrition effects generally encountered in mechanical
agitated reactors. It is ideally suited for aerobic cultures since oxygen mass
transfer coefficient are quite high in comparison to stirred tank reactors.
This is ideal for SCP production from methanol as carbon substrate. This is
used mainly to avoid excess heat produced during mechanical agitation.
bioreactors (FBB) have received increased attention in the recent years due to
their advantages over other types of reactors. Most of the FBBs developed for
biological systems involving cells as biocatalysts are three phase systems
(solid, liquid & gas). The fundamentals of three phase fluidization
phenomena have been comprehensively covered in chemical engineering literature.
The FBBs are generally operated in co-current upflow with liquid as continuous
phase and other more unusual configurations like the inverse three phase
fluidized bed or gas solid fluidized bed are not of much importance. Usually
fluidization is obtained either by external liquid re-circulation or by gas fed
to the reactor. In the case of immobilized enzymes the usual situation is of
two-phase systems involving solid and liquid but the use of aerobic biocatalyst
necessitate introduction of gas (air) as the third phase. A differentiation
between the three phase fluidized bed and the airlift bioreactor would be made
on the basis that the latter have a physical internal arrangement (draft tube),
which provides aerating and non-aerating zones. The circulatory motion of the
liquid is induced due to the draft tube.
Packed bed or fixed bed
bioreactors are commonly used with attached biofilms especiallyin wastewater
engineering. The use of packed bed reactors gained importance after the
potential of whole cell immobilization technique has been demonstrated. The
immobilized biocatalyst is packed in the column and fed with nutrients either
from top or from bottom. One of the disadvantages of packed beds is the changed
flow characteristic due to alterations in the bed porosity during operation.
While working with soft gels like alginates, carragenan etc the bed compaction
which generally occurs during fermentation results in high pressure drop across
the bed. In many cases the bed compaction was so severe that the gel integrity
was severely hampered. In addition channeling may occur due to turbulence in
the bed. Though packed beds belong to the class of plug flow reactors in which
backmixing is absent in many of the packed beds slight amount of backmixing
occurs which changes the characteristics of fermentation. Packed beds arc
generally used where substrate inhibition governs the rate of reaction. The
packed bed reactors are widely used with immobilized cells. Several
modifications such as tapered beds to reduce the pressure drop across the
length of the reactor, inclined bed, horizontal bed, rotary horizontal reactors
have been tried with limited success.
Bubble column fermenter
is a simplest type of tower fermenter consisting of a tube which is air sparged
at the base. It is an elongated non-mechanically stirred fermenter with an
aspect ratio of 6:1. This type of fermenter was used for citric acid
Milk is an excellent
source of for humans and bacteria. It is full of vitamins, fats, minerals,
nutrients and carbohydrates. It is rich in the protein, casein, which gives
milk its characteristic white color. The most abundant carbohydrate is the
disaccharide lactose, “milk sugar.” At room temperature, milk undergoes natural
souring caused by lactic acid produced from fermentation of lactose by
fermentative lactic acid bacteria. This accumulation of acid (H+ ions)
decreases the pH of the milk and cause the casein to coagulate and curdle into
curds and whey. Curds are large, white clumps of casein and other proteins.
Whey is the yellow liquid that is left behind after the casein has formed
curds. Thus, bacteria obtain nutrients from the milk, inadvertently curdle it
and humans use it as the first step in making many dairy products.
The microbes important
for dairy product manufacturing can be divided into two groups, primary and
secondary microflora. Products undergoing fermentation by only primary
microflora are called unripened and those processed by both primary and
secondary microflora are called ripened. Primary microflora are fermentative
lactic acid bacteria which cause the milk to curdle. During dairy product
production, milk is first pasteurized to kill bacteria that cause unwanted
spoilage of the milk and of the downstream milk products.
consists of certain kinds of Lactococcus,Lactobacillus and Streptococcus that are intentionally added to pasteurized milk and
grown at 30°C or 37°C (temperature depends on the bacteria added).
include several different types of bacteria (Leuconstoc, Lactobacillus
and Propionibacterium), yeasts and
molds; they are only used for some types of surface ripened and mold ripened
cheeses. The various combinations of microflora determine what milk product you
will end up with.
milk products are created using various starting products and bacteria:
For buttermilk production, Lactobacillus bulgaris (named for its
country of discovery, Bulgaria) is added to skim milk to curdle it. Leuconosoc is then added to thicken it.
Sour cream making also involves the same
methodology as above, instead the starting material is cream instead of skim
To produce yogurt, dry milk protein is
added to milk to concentrate the milk before addition of actively growing Streptococci and Lactobacilli.
Butter is produced by the curdling and
slight souring due to Streptococci
growing in sweet cream. Leuconostocis
then added so it can synthesize the compound diacetyl which gives butter its
characteristic aroma and taste. Subsequently, the milk undergoes churning to
aggregate the fat globules into solidified butter.
Therefore, the type of
milk and the bacteria involved in fermentation will determine the dairy product
In this write up, we
are disscussing cheese as the fermened dairy product. Cheese is an important
product of fermentative lactic acid bacteria. Particularly in the past, cheese
was valued for its long shelf life. Due to its reduced water content, and
acidic pH, bacterial growth is severely inhibited. This causes cheese to spoil
much more slowly than other milk products. Consequently, the art of cheese
production has spread throughout Europe, each country manufacturing many
different types of cheeses.
cheese factories accept either morning milk (which is richer), evening milk, or
both. Because it is generally purchased from small dairies which don’t
pasteurize, this milk contains the bacteria necessary to produce lactic acid,
one of the agents that triggers curdling. The cheese makers let the milk sit
until enough lactic acid has formed to begin producing the particular type of
cheese they’re making. Depending on the type of cheese being produced, the
cheese makers may then heat the ripening milk. This process differs slightly at
large cheese factories, which purchase pasteurized milk and must consequently
add a culture of bacteria to produce lactic acid.
the Curds from the Whey
next step is to add animal or vegetable rennet to the milk, furthering its
separation into curds and whey. Once formed, the curds are cut both vertically
and horizontally with knives. In large factories, huge vats of curdled milk are
cut vertically using sharp, multi-bladed, wire knives reminiscent of oven
racks. The same machine then agitates the curds and slices them horizontally.
If the cutting is done manually, the curds are cut both ways using a large,
two-handled knife. Soft cheeses are cut into big chunks, while hard cheeses are
cut into tiny chunks. (For cheddar, for instance, the space between the knives
is about one-twentieth of an inch half a centimeter.) After cutting, the
curds may be heated to hasten the separation.
must then be removed from the curds, although the amount removed depends on the
type of cheese. For some types with high moisture contents, the whey-draining
process removes sufficient moisture. Other types require the curds to be cut, heated,
and/or filtered to get rid of excess moisture.
make cheddar cheese, for example, cheese makers cheddar, or finely chop, the curd. To make hard, dry
cheeses such as parmesan, cheese makers first cheddar and then cook the curd.
Regardless, if the curds are to be aged, they are then put into molds. Here,
they are pressed to give the proper shape and size. Soft cheeses such as
cottage cheese (paneer) are not aged.
4. Aging of
this stage the cheese may be inoculated with a flavoring mold, bathed in brine,
or wrapped in cloth or hay before being deposited in a place of the proper
temperature and humidity to age. Some cheeses are aged for a month, some for up
to several years. Ageing sharpens the flavor of the cheese; for example,
cheddar aged more than two years is appropriately labeled extra sharp.
cheeses may develop a rind naturally, as their surfaces dry. Other rinds may
form from the growth of bacteria that has been sprayed on the surface of the
cheese. Still other cheeses are washed, and this process encourages bacterial
growth. In place of or in addition to rinds, cheeses can be sealed in cloth or
wax. For local eating, this may be all the packaging that is necessary.
However, large quantities of cheese are packaged for sale in distant countries.
Such cheeses may be heavily salted for export (such as Roquefort) or sealed in
impermeable plastic or foil.
Making and Wrapping of Processed Cheese
yet inferior cheeses can be saved and made into processed cheese. Cheeses such
as Emmental (commonly called Swiss), Gruyere (similar to Swiss), Colby, or
cheddar are cut up and very finely ground. After this powder has been mixed
with water to form a paste, other ingredients such as salt, fillers,
emulsifiers, preservatives, and flavorings are added. The mixture is then
heated under controlled conditions. While still warm and soft, the cheese paste
is extruded into
long ribbons that are sliced. The small sheets of cheese are then put onto a
plastic or foil sheet and wrapped by a machine.
Advantages of Fermented Foods
Improves Digestion: Fermentation breaks down nutrients into
more easily digestible forms. When lactobacilli in fermented foods proliferate,
their vitamin levels increase and digestibility is enhanced..
Suppression of H. pylori: Helicobacter pylori infection is an
important risk factor for many gastrointestinal diseases. Some fermented foods
serve useful for suppressing H. pylori infection.An observational study
published in World Journal of Gastroenterologyinvolving 464
participants found lower prevalence of H. pylori seropositivity in those who
consumed yogurt more than once a week compared to those who did not. This
confirms other research findings that fermented milk improves gastrointestinal
symptoms in patients who tested positive for H. pylori.
Anticancer Effects: Researchers believe probiotic cultures and
fermented foods might decrease the exposure to chemical carcinogens by:
detoxifying the ingestion of carcinogens
altering the environment of the intestine and decreasing
metabolic activities or populations of bacteria that may generate carcinogenic
producing metabolic products that cause programmed cell death or
producing compounds that inhibit the growth of tumor cells
stimulating the immune system to defend itself against cancer
Reduces Symptoms of Lactose Intolerance: Lactobacillus consumes lactose in milk and transforms it into
lactic acid that may be easier for individuals to digest. Lactic acid in yogurt
reduces symptoms of lactose intolerance in individuals who are
lactase-deficient. The beneficial effect appears to be a result of the lactic
acid bacteria in fermented milk, increasing lactase in the small intestine.
Arthritis Symptoms: It
is thought that inflammation associated with rheumatoid arthritis may be
modulated by the consumption of fermented foods.
6. Nutritional Content: High protein and calcium content,
different varieties and hence different tastes for numerous dishes, contains
fat soluble vitamins such as A, D, E and K.
Disadvantages of fermented foods
1. Development of
gastric cancer: A study was published
in Cancer Science in January 2011 showing a connection between the consumption
of fermented foods and the risk of developing gastric cancer. The study was a
meta-analysis of reports showing the effects of fermented and non-fermented soy
food consumption on the risk of gastric cancer development. The study indicated
that a high intake of fermented soy foods increased the risk of gastric cancer
while a diet that was high in non-fermented soy foods reduced the risk of
2. Store-bought items lose beneficial
bacteria: Fermented foods sold in many stores are
processed differently than those that are traditionally fermented. They have
too much acid and have been pasteurized so they don’t spoil right away.
Research has also shown that fermented cheese products contain way too much
salt than water.
High Fat Content:High trans fat content leading to numerous
health problems like heart attacks, strokes due to its deposition on blood
vessels and even cause prostate and breast cancer when consumed in long term
eating fermented foods certainly has some disadvantages, it doesn’t mean that
we have to completely avoid it. A normal recommended intake is sure to provide
positive effects on health.