Fermentation is a metabolic process used by microorganisms to break down organic compounds in the absence of oxygen. Major fermentation pathways include lactic acid fermentation, alcohol fermentation, and mixed acid fermentation. Lactic acid fermentation produces lactic acid, alcohol fermentation produces ethanol and carbon dioxide, and mixed acid fermentation produces various acids. Fermentation is regulated by enzymes and plays a significant role in various foods and beverages as well as human physiology.

2. https://www.youtube.com/watch?v=1vwfGxVWYNk&t=92s
https://www.youtube.com/watch?v=CMWZgqhsUSM
https://www.youtube.com/watch?v=XREALVgxBEI

3. Overview;
Introduction
Fermentation
Fermentative Pathway
Fermentative Pathway
Lactic Acid Fermentation
Alcohol Fermentation
Mixed Acid Fermentation
2,3-Butandiol Fermentation
Clostridial Fermentation
Propionic Acid Fermentation
Regulation
Significance of Fermentation
Conclusion

4. FERMENTATION:
All the favourite items we consume everyday are probably the products of dead
microorganism. These are the cultures of Probiotic bacteria meaning “Good
germs”. They basically need the organic compounds from the rotten foods
which we throw and convert into an edible compound. It is all because of
Fermentation.
Fermentation is a metabolic process occuring in these kinds of bacteria and our
ancesters were the first to use while eating. They used to eat grapes fallen on
the ground and shockingly, it tasted much better and now we call this drink
“Wine”.
After the invention of microscope by Antoinne van Leeuwenhoek, German
chemist Justus Von Liebig had theorized Fermented foods to be a product from
decay and death of microorganism. However, Later in 1857, Louis Pasteur
demonstrated Wine to be the product of decomposition of Yeast into Lactic
acid, resulting in addition of sour taste to Wine.

5. FERMENTATIVE PATHWAYS
Fermentation is an anaerobic process involving breakdown of glucose
in absence of Oxygen.
It begins with Glycolysis with extraction of energy with some reactions
after it, This reaction is the fermentative pathway involving different
products.
However, Electron Transport Chain does not run in Fermentation. So,
the NADH does not transfer to NAD+ in Fermentation and Citric acid
cycle does not take place. Furthermore, the extra reactions in
Fermentation is to generate NAD+ from NADH. It is to maintain the
steady supply of NAD+ in Fermentation

6. Lactic Acid Fermentation
End Product: Lactic Acid bacteria
Common in : Lactic acid bacteria (lactobacillus, lactococcus)
Two patterns may be observed:
1: Homofermentative pathway: which yields lactic acid as an only fermentative
product,
Lactobacillus delbrueckii and S. thermophiles used in yogurt production
----These bacteria contain Aldolase enzyme
----Two ATP is formed
2: Heterofermentative pathway: In addition to Lactic acid, Ethanol, Carbon dioxide is
also formed
-----These bacteria do not contain Aldolase enzyme an cannot breakdown fructose
bisphosphate to triose phosphate. Instead oxidize Glucose 6 Phosphate to 6-
phosphogluconate and decarboxylate to pentose phosphate.
----It occurs in Leuconostoc mesenteroides
------Only one ATP is produced
Diagram

7. Homofermentative Heterofermentative
Back

8. Alcohol fermentation
End product: Ethanol and CO2
Common in: Yeast
The first part is the Glycolysis which involves
breakdown of glucose to
two pyruvate molecule with the
involvement of electron acceptors in between
The second part is the Fermentation,
In the first reaction
the enzyme pyruvate decarboxylase which,
releasing CO2 gas and the removes
a carboxyl group from pyruvate
two-carbon molecule acetaldehyde
In the second reaction,
the enzyme alcohol dehydrogenase,
transfers an electron from NADH to acetaldehyde,
producing ethanol and NAD+ Back

9. Mixed Acid Fermentation
End Products : Different kinds of Acids
Common : bacteria belonging to
Enterobacteriaceae family
At first pyruvate is cleaved
by the enzyme
Pyruvate formate lyase
to yield formic acid
and Acetyl coA
----the formic acid converts into
acetic acid, lactic acid,
succinic acid,
ethanol or CO2 and water
depending on the occurring pathway
----Formic acid: Intermediate product i
Back

10. 2,3- Butanediol fermentation
End product :2,3- Butanediol
Common in : facultative anaerobes like Klebsiella spp. And Enterobacter spp
Pyruvate of Glycolysis
undergoes condensation
to α-acetolactate
The α-acetolactate
undergoes decarboxylation
in the presence of enzyme
pyruvate decarboxylase to produce
Acetoin (acetyl methylcarbainol)
which is reduced by
NADH2 to form 2,3-butanediol.
Back

11. Clostridial fermentation:
End product: Butyric acid is a major product. However, some species produce
acetone and butanol
At first Clostridium spp convert pyruvate into AcetylcoA aerobically.
Two molecule of acetylcoA condenses in the presence of enzyme acetyl-transferase
to from AcetoacetylcoA.
AcetoacetylCoA is reduced to β-hydroxybutyrylcoA by NADH2 in the presence of
enzyme hydroxybutyrate dehydrogenase.
β-hydroxybutyrylcoA is reduced by enoylcoA hydratase to form CrotonylcoA and
water.
CrotonylcoA is further reduced to butyrylcoA by an enzyme NAD-linked
dehydrohenase.
ButyrylcoA and acetate act together with fatty acid coA transferase to form
acetylcoA and butyrate.
Acetyl coA then recycle in the reaction
Structure

12. Next

13. Some proteolytic Clostridium spp. can ferment amino acids,
these clostridia degrade proteins from dead organisms
Depending on species, proteolytics clostridia ferment individual amino acids such
as glutamate, glycine, alanine, cysteine, histidine, serine, threonine.
The amino acids are catabolized in such a way that eventually yields a fatty acid—
CoA derivative, typically acetyl (C2), Butyryl(C4), or Caproyl(C6).
Other amino acid fermentation include ammonia and carbon dioxide.
Some Clostridia can ferment pairs of ammonia acid.
This coupled amino acid fermentation is called Stickland reaction.
For example, Clostridium sporogenes ferment glycine and alanine in which alanine
is electron donor and glycine is the electron acceptor.
Structure

14. Others

15. Propionic Acid Fermentation
End Product: Propionic acid
as a major fermentation product.
Lactate, is probably the major substrate
for propionic acid bacteria
Common in: Propionibacterium
Pyruvate reacts with methyl malonyl coA
to form Propionyl coA and Oxaloacetate.
Oxaloacetate give rise to malate,
fumarate and succinate
by reverse TCA cycle
. Propionyl coA transfer its coA
to succinate to form
succinylcoA and propionate Back

16. Regulation:
Since, Fermentation begins with a small process of Glycolysis, the third step is
the most important one as it is catalyzed by Phosphofructokinase(PFK) which is
regulated by ATP, AMP, Citrate and some other molecules.
-ATP: ATP is the negative regulator of PFK. If there is plenty of ATP, Glycolysis
does not need to make more.
- AMP: Adenosine monophosphate (AMP) is a positive regulator of PFK. When a
cell is very low on ATP, it will start squeezing more ATP out of ADP molecules by
converting them to ATP and AMP (ADP + ADP → ATP + AMP). High levels of AMP
mean that the cell is starved for energy, and that glycolysis must run quickly to
replenish ATP.
- Citrate: Citrate, the first product of the citric acid cycle, can also inhibit PFK. If
citrate builds up, this is a sign that glycolysis can slow down, because the citric
acid cycle is backed up and doesn’t need more fuel.

17. Significance
1. Muscles cells carry out Lactic acid fermentation during times of hard exercises.
These Lactic acid is transported to Liver through bloodstreams and converted back to
Pyruvate by lactate dehydrogenase and energy is released
2. The Lactic acid bacteria present in milk, cheese and other dairy products can be of a
great benefit especially for those who are Lactose intolerant. The Lactic acid bacteria
converts the Lactose sugar into digestable Lactic acid. Researches reported of a women
with improved gastrointestinal digestive symptoms when fermented milk
containing Bifidobacterium lactis was consumed
3. . Fermentation helps create new nutrients, like B vitamins, folic acid, riboflavin,
niacin, thiamine and biotin, and has been shown to improve the availability,
digestibility of some dietary nutrients. The availability of fat and proteins are enhanced
and the production of lactic acid, butyric acid, free amino acids and short chain fatty
acids are increased.

18. 4. Several reports are on way saying Fermented foods can treat Cancer.
Studies in the Netherlands and Sweden have observed the effects of regular
consumption of fermented dairy products in reducing the risk of bladder cancer.
Lactobacillus prevent toxicity of heavy metals by excreting harmful heavy metals
and heterocyclic aromatic amines, carcinogens found in overcooking meat.
Kimchi, a fermented cabbage cuisine, contains strains that promote the
degradation of organophosphorus pesticides, by breaking down a cancer-causing
food preservative called sodium nitrate.
Fermented foods like kimchi, sauerkraut and jun tea also help your liver to banish
any build up of heavy metals in your system

19. Conclusion
From bread to butter, sausage to sauce, wine to kimchi, fermented foods are all
around us and the living organisms might be thinking of more ways to reshape
our world. The art of our ancestors has turn into beautiful cultures like the
Nukadoko for the Japanese and Gundruk for Nepalese. Despite of our
consumption everyday, the scientific knowledge makes it more difficult and
intuitive. But it’s precisely this magic of ancestors that would make us think in
different way. Integrating with fermented foods in our daily life would be messier
but more caring to many life forms with whom we co-exist with. As we see that
all these organism responsible for fermentation need a simple organic
compound present in the raw foods we throw and create miracle out of it.
Perhaps rather than pondering for transition of life and death we could just lend
a world as for contemplation.

22. Nukadoko

23. Sauerkraut