Types of Fermentation

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What is Fermentation?

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All living beings need the energy to perform various important functions. This energy is derived from respiration. Respiration may or may not occur in the presence of oxygen. When respiration takes place in the presence of oxygen, it is termed as aerobic respiration and when it takes place in the absence of oxygen it is called anaerobic respiration. Most of the living organisms derive energy by aerobic respiration, but a few organisms like bacteria, yeast, etc. respire anaerobically. These organisms derive energy in the absence of oxygen by converting starch or sugar to alcohol or an acid. This enzyme-catalyzed metabolic process is called fermentation.


Fermentation is a biochemical process taking place in some organisms. The beginning of this process is similar to cellular respiration. That is the formation of pyruvic acid by the process of glycolysis where net 2 ATP molecules are synthesized. Further, pyruvate is reduced to lactic acid, ethanol, or other products. The NAD+ formed in the process is further re-utilized in the process of glycolysis.


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Types of Fermentation

Fermentation is of two types, depending upon the number of end products.

  • Homo Fermentation - In this type, only one end product is formed.

  • Hetero Fermentation - In this type, more than one end product is formed.

Different end products are formed at the end of fermentation and depending upon the type of end product formed, fermentation is categorized into various types:

1. Lactic Acid Fermentation

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Lactic acid fermentation is a process by which glucose and other sugars containing six carbon atoms turn into metabolite lactate and cellular energy. This type of anaerobic fermentation mostly occurs in bacteria, certain animal cells, mammalian red blood cells, and sometimes in skeletal muscles under conditions of insufficient oxygen supply to allow continuity of aerobic respiration. In this process lactic acid forms from pyruvate produced during glycolysis. NAD+ is generated from NADH and lactate dehydrogenase catalyzes the reaction. The lactic acid formed by anaerobic respiration during exercise gets accumulated in the cell and causes fatigue.


2. Alcohol Fermentation

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Alcohol fermentation is also called ethanol fermentation because the end product in this case is ethanol. It is mostly carried out by yeast to convert simple sugars into carbon dioxide and ethanol. It is widely used in industries to produce wine, beer, biofuel, etc. In this process, pyruvic acid is broken down into acetaldehyde and the carbon dioxide is released. The acetaldehyde thus formed, gives ethanol. NAD+ is also formed from NADH which later enters glycolysis. Two enzymes catalyze the two steps of the process. These are pyruvic acid decarboxylase and alcohol dehydrogenase.


3. Acetic Acid Fermentation

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Acetic acid fermentation is the process used in the formation of vinegar. The two-step process involves the following steps:

  • Formation of ethyl alcohol anaerobically from sugar by using yeast.

  • Oxidation of ethyl alcohol to give acetic acid using acetobacter by aerobic respiration.


4. Butyric Acid Fermentation

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The bacteria carrying out butyric acid fermentation are obligately anaerobic and spore-forming bacteria belonging to the genus Clostridium. It is also known as mixed acid fermentation because along with butyric acid, n-butanol, acetic acid, ethanol, isopropanol, and acetone are also formed depending upon the species carrying out the process.

This type of fermentation is used to carry out the following processes:

  • Retting of jute fiber

  • Rancid butter

  • Tobacco processing

  • Tanning of leather

In the first step, oxidation of sugar gives pyruvate by the process of glycolysis. In the next step, pyruvate is oxidized to form acetyl-CoA with the help of the oxidoreductase enzyme and produces CO2 and H2. Finally, acetyl-CoA is further reduced to form butyric acid. Butyric Acid fermentation yields more energy with the formation of net 3 molecules of ATP.


Uses of Fermentation

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Fermentation is one of the oldest metabolic processes commonly used by prokaryotes and eukaryotes. It is also a process used in industries to manufacture various products. Various types of fermentation are used to produce the desired end product for use. Common products we use in our day to day life produced by fermentation include:

  • Wine

  • Beer

  • Biofuels

  • Yogurt

  • Pickles

  • Bread

  • Lactic Acid containing sour foods

  • Certain vitamins and antibiotics

  • Vinegar

  • Condiments like apple cider vinegar, kombucha, etc.


Advantages of Fermentation

Fermented food tastes better, is easy to digest and nutritious for the body. Benefits of consuming fermented food are as follows:

  • Fermented food helps maintain the stomach bacteria, thus helping digestion.

  • It has an anti-carcinogenic effect.

  • It is good for the immune system.

  • It is also beneficial for lactose-intolerant people.

There are many more applications of fermentation than industrial and domestic. For example - It is used to produce methane in sewage treatment plants.

FAQ (Frequently Asked Questions)

1. What are the Types of Fermentation?

Ans. Depending upon the type of end product formed, fermentation is categorized as:

  • Lactic Acid Fermentation

  • Alcohol fermentation

  • Butyric acid fermentation

  • Acetic Acid fermentation

2. What are the Advantages of Eating Fermented Food?

Ans. Fermented food tastes better, is easy to digest and nutritious for the body. Benefits of consuming fermented food are as follows:

  • Fermented food helps maintain the stomach bacteria, thus helping digestion

  • It has an anti-carcinogenic effect.

  • It is good for the immune system

  • It is also beneficial for lactose-intolerant people

3. Why is Butyric Acid Fermentation Called Mixed Acid Fermentation?

Ans. Butyric acid fermentation is also known as mixed acid fermentation because along with butyric acid, n-butanol, acetic acid, ethanol, isopropanol, and acetone are also formed depending upon the species carrying out the process.