University of Diyala
College of Engineering
Department of Chemical
Engineering
Fermentation
Name: Hussein Ali Ibrahim
Stage: The third
Fermentation: _
Fermentation is a metabolic process that produces chemical changes
in organic substrates through the action of enzymes.
In biochemistry, it is narrowly defined as the extraction of energy
from carbohydrates in the absence of oxygen. In the context of food
production, it may more broadly refer to any process in which the
activity of microorganisms brings about a desirable change to a
foodstuff or beverage. The science of fermentation is known as
zymology.
In microorganisms, fermentation is the primary means of producing
adenosine triphosphate (ATP) by the degradation of organic
nutrients anaerobically. Humans have used fermentation to produce
foodstuffs and beverages since the Neolithic age.
For example, fermentation is used for preservation in a process that
produces lactic acid found in such sour foods as pickled cucumbers,
kombucha, kimchi, and yogurt, as well as for producing alcoholic
beverages such as wine and beer. Fermentation also occurs within
the gastrointestinal tracts of all animals, including humans.
Below are some definitions of fermentation.
1. Preservation methods for food via microorganisms (general
use).
2. Any large-scale microbial process occurring with or without air
(common definition used in industry).
3. Any process that produces alcoholic beverages or acidic dairy
products (general use).
4. Any energy-releasing metabolic process that takes place only
under anaerobic conditions (somewhat scientific).
5. Any metabolic process that releases energy from a sugar or other
organic molecule, does not require oxygen or an electron
transport system, and uses an organic molecule as the final
electron acceptor (most scientific).
IMPORTANCE OF FERMENTATION: _
Fermentation is important to cells that don't have oxygen or cells
that don't use oxygen because:
1- It allows the cells to get 2 ATP gain from one molecule of glucose,
even without oxygen.
2- Fermentation takes away the end products of glycolysis so
glycolysis can continue ... freeing up the electron carriers, and so
on.
3- Fermentation is important to the baking industry because it is the
process that yeast uses to produce the bubbles of carbon dioxide
that make the dough rise.
4- Fermentation is important in wineries and breweries because
yeast uses fermentation to produce alcohol.
5- Fermentation is important in muscles because it allows the
muscles to keep getting a little energy from glucose even when
the oxygen supply can't keep up with the demand.
Type of Fermentation: _
1. AEROBIC FERMENTATION
Aerobic respiration refers to the set of chemical reactions associated
with the production of energy by completely oxidizing food. It
releases carbon dioxide and water as by-products. Aerobic respiration
occurs mainly in animals and higher plants. It is the most efficient
process among different energy production processes. The three
steps of aerobic respiration are decomposition, the Krebs cycle, and
the electron transport chain.
A- Glycolysis is the first step in aerobic respiration, which takes place
in the cytoplasm. This process breaks down glucose into two
pyruvate molecules. Pyruvate molecules undergo oxidative
decarboxylation to form acetyl-CoA. 2ATP and 2 NADH are the
results of this process.
B- The Krebs cycle occurs within the mitochondrial matrix. The
complete breakdown of acetyl COA into carbon dioxide occurs in
the Krebs cycle, resulting in regeneration of the starting compound,
oxaloacetate. During the Krebs cycle, the release of energy from
acetyl-CoA results in 2 GTPs, 6 NADH, and 2 FADH2.
C- Electron transport chain ATP is used during the phosphorylation
process that consists of the temporary production of NADH and
FADH2. It occurs in the inner mitochondrial membrane.
C6H12O6 + 6O2 → 6CO2 + 6H2O + 36ATP
2- Anaerobic fermentation
Fermentation refers to the chemical decomposition of organic
substrates by microorganisms into ethanol or lactic acid in the
absence of oxygen. Fermentation occurs at the site of the cytoplasm
in microorganisms such as yeast, helminths and bacteria. Two steps
of fermentation are glycolysis and partial oxidation of pyruvate. Based
on the pyruvate oxidation pathway, fermentation consists of two
types; Ethanol fermentation and lactic acid fermentation. The net
yield of fermentation is only 2 ATPs.
A- Ethanol fermentation occurs mainly in yeast in the absence of
oxygen. In this process, the removal of carbon dioxide leads to the
decarboxylation of pyruvate to acetaldehyde. Then acetaldehyde
is converted to ethanol using the hydrogen atoms of NADH.
Exhaustion results from the release of carbon dioxide into the
medium. The balanced chemical equation for ethanol
fermentation is as follows:
C6H12O6 → 2C2H5OH + 2CO2 + 2ATP
Ethanol fermentation has used the production of beer, wine, and
bread. It's worth noting that fermentation in the presence of high
levels of pectin results in the production of small amounts of
methanol, which is toxic when consumed.
B- Lactic acid ( )حامض اللبنيكthe pyruvate molecules from glucose
metabolism (glycolysis) may be fermented into lactic acid. Lactic
acid fermentation is used to convert lactose into lactic acid in
yogurt production. It also occurs in animal muscles when the tissue
requires energy at a faster rate than oxygen can be supplied. The
next equation for lactic acid production from glucose is:
C6H12O6 → 2C3H6O3 + 2ATP
C6H12O6 (glucose) → 2 CH3CHOHCOOH (lactic acid)
C12H22O11 (lactose) + H2O (water) → 4 CH3CHOHCOOH (lactic acid)
c- Hydrogen and Methane Gas Production. The process of
fermentation may yield hydrogen gas and methane gas.
Methanogenic archaea undergo a disproportionation reaction in
which one electron is transferred from a carbonyl of a carboxylic acid
group to a methyl group of acetic acid to yield methane and carbon
dioxide gas. Many types of fermentation yield hydrogen gas. The
product may be used by the organism to regenerate NAD+ from
NADH. Hydrogen gas may be used as a substrate by sulfate reducers
and methanogens. Humans experience hydrogen gas production
from intestinal bacteria, producing flatus.
What Are the Different Stages of the Fermentation
Process?
Depending upon what you’re fermenting, the process can have
several stages.
Primary fermentation. In this brief phase, microbes begin rapidly
working on raw ingredients such as fruit, vegetables, or dairy. The
microbes present or in the surrounding liquid (such as brine for
fermented vegetables) prevent putrefying bacteria from colonizing
the food instead. Yeasts or other microbes convert carbohydrates
(sugars) into other substances such as alcohols and acids.
Secondary fermentation. A term often referred to in winemaking and
brewing circles, refers to a longer stage of fermentation that takes
place over several days or weeks. Secondary fermentation occurs
when many yeasts and microbes start to die off and their available
food source (the carbohydrates) becomes more scarce.
At this stage, the pH of the ferment may be significantly different from
when it started out, which also affects the chemical reactions taking
place between the microbes and their environment.
What Happens During the Fermentation Process?
Fermentation occurs in the absence of oxygen (anaerobic conditions),
and in the presence of beneficial microorganisms (yeasts, molds, and
bacteria) that obtain their energy through fermentation. If enough
sugar is available, some yeast cells, such as Saccharomyces cerevisiae,
prefer fermentation to aerobic respiration even when oxygen is
abundant.
-During the fermentation process, these beneficial microbes break
down sugars and starches into alcohols and acids, making food more
nutritious and preserving it so people can store it for longer periods
of time without it spoiling.
-Fermentation products provide enzymes necessary for digestion.
This is important because humans are born with a finite number of
enzymes, and they decrease with age. Fermented foods contain the
enzymes required to break them down.
-Fermentation also aids in pre-digestion. During the fermentation
process, the microbes feed on sugars and starches, breaking down
food before anyone’s even consumed it.
What Are the Advantages of Fermentation?
Fermented foods are rich in probiotics, beneficial microorganisms
that help maintain a healthy gut so it can extract nutrients from food.
1-Probiotics aid the immune system because the gut produces
antibiotic, anti-tumor, anti-viral, and antifungal substances, and
pathogens don’t do well in the acidic environment fermented foods
create.
2-Fermentation also helps neutralize anti-nutrients like phytic acid,
which occurs in grains, nuts, seeds, and legumes and can cause
mineral deficiencies. Phytates also make starches, proteins, and fats
less digestible, so neutralizing them is extremely beneficial.
3-Fermentation can increase the vitamins and minerals in food and
make them more available for absorption. Fermentation increases B
and C vitamins and enhances folic acid, riboflavin, niacin, thiamin, and
biotin. The probiotics, enzymes, and lactic acid in fermented foods
facilitate the absorption of these vitamins and minerals into the body.
4- Preserves and enriches food, improves digestibility, and enhances
the taste and flavour of foods. And Potential of enhancing food safety
by controlling the growth and multiplication of a number of
pathogens in foods.
Managing Fermentation
Microbes typically like to work in a warm, room temperature
environment. The exact temperature range will vary based on the
types of microbes involved and product that's being fermented.
Changing the temperature can have a big impact on fermentation.
Moving a fermenting product to a cooler temperature, for example
by placing it in the fridge, will slow down the rate of fermentation
or stop it altogether. Heating a ferment too much may kill the
microbes doing the fermentation.
Commercial fermentation requires specialist equipment such as
fermentation tanks for brewing beer, for example. Using special
equipment enables fermentation to be controlled and
standardized at scale.
Methods of Fermentation
1- BATCH FERMENTATION
- A tank of fermenter is filled with the prepared mash of raw
materials to be fermented. The temperature and pH for
microbial fermentation is properly adjusted, and occasionally
nutritive supplements are added to the prepared mash. The
mash is steam- sterilized in a pure culture process.
- The inoculums of a pure culture is added to the fermenter,
are taken out for further processing.
- The fermenter is cleaned and the process is repeated. Thus
each fermentation is a discontinuous process divided into
batches.
2- CONTINUOUS FERMENTATION
- Growth of microorganisms during batch fermentation confirms to the
characteristic growth curve, with a lag phase followed by a logarithmic
phase. Is because of limitation of one or more of the essential nutrients.
This, in tum, is terminated by progressive decrements in the essential
nutrients.
- In continuous fermentation, the substrate is added to the fermenter
continuously at a fixed rate. This maintains the organisms in the
logarithmic growth phase.
References
1- "The Alcohol Content of Bread". Canadian Medical
Association Journal. 16 (11): 1394–5. November 1926.
2- Bowen, Richard. "Microbial Fermentation". Hypertexts for
biological sciences. Colorado State University. Retrieved
29 April 2018.
3- Breda, E (2014). The Evolution of the Bioenergetics
Processes. Progress in Biophysics and Molecular Biology.
21. Elsevier.
4- Sharma, K.R. Design and operational key factors of
bioreactor. Biotech Articles.2012.
5- Lateef, A.; Kana, M.Z.; EB, G.K.; J.K, O. Constructional
features of a 15-litre homemade bioreactor for fed-batch
fermentations. African Journal of Biotechnology. 2003, 2,
233-6.
6- Martin, I.; Wendt, D.; Heberer, M.Th. role of bioreactors in
tissue engineering. Trends in biotechnology. 2004, 22,
7- McNeil, B.; Harvey, L. eds. Practical fermentation
technology. John Wiley & Sons. 2008.
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