Fermentation: Anaerobic Respiration

Fermentation is a type of anaerobic respiration. It occurs when oxygen is not present. It is a chemical reaction that takes place in all living cells. Fermentation is an important part of food production as well, as it helps to make alternative protein sources. The process involves the breaking down of glucose in the absence of oxygen.

Let us discuss further about the fermentation process in detail going further.

What is Fermentation?

Fermentation is a type of respiration that occurs in the absence of oxygen. It usually occurs in the yeast cells and bacteria and also in the muscles of animals. Fermentation is an anaerobic pathway, where the breakdown of glucose takes place.

Fermentation is one of the pathways through which cells can perform anaerobic respiration. During fermentation, energy in the form of ATP is released, without using oxygen.

What Happens in Fermentation?

Fermentation typically takes place in the micro-organisms like yeast and bacteria. Here is what is happening in the fermentation process.

Glycolysis

• The step starts with the breakdown of glucose or sugar.
• Glucose converts into pyruvate and produces a small amount of energy in the form of ATP.
• The process requires no oxygen.

Regeneration of NAD+

• In the absence of oxygen, cells need a way to regenerate NAD⁺ from NADH (produced during glycolysis).
• This is crucial because NAD⁺ is needed for glycolysis to continue.
• During fermentation, NADH donates electrons to pyruvate, regenerating NAD⁺.

Pyruvate Conversion

• In the presence of oxygen, pyruvate enters the mitochondria and is converted into acetyl-CoA.
• This is achieved by the enzyme pyruvate dehydrogenase.
• Acetyl-CoA then enters the Krebs cycle (citric acid cycle).
• It is further oxidized to produce ATP, NADH, and FADH₂.
• In the case of aerobic fermentation – Pyruvate+NAD++CoA→Acetyl-CoA+CO2​+NADH
• In the absence of oxygen, cells rely on fermentation to regenerate NAD+.
• Pyruvate is converted into different products based on the type of fermentation.
• Yeast and certain bacteria metabolise pyruvate to acetaldehyde, followed by ethanol (alcohol) and CO₂.
• In the case of aerobic fermentation – Pyruvate+NADH→Lactic Acid+NAD

What are the Types of Fermentation?

Fermentation is of two types depending on the type of byproduct produced. Here is a closer look at the types of fermentation given below.

Lactic acid fermentation

In this type of fermentation, pyruvate from glycolysis is reduced to form lactate or lactic acid. This is achieved with the help of the enzyme lactate dehydrogenase.

• This fermentation occurs in certain bacteria like – Lactobacillus.
• In the case of muscle cells of animals, when oxygen is scarce, during intense exercise, lactic acid fermentation is observed.
• The byproduct of the fermentation is lactic acid.
• Regeneration of NAD+ takes place.
• This allows glycolysis to continue and produce ATP in anaerobic conditions.
• For example – in human muscles, after a heavy workout of running, temporary fatigue occurs due to lactic acid fermentation.
• In food, lactic acid fermentation helps in making yoghurt, sourdough bread, and sauerkraut.
• Reaction – Pyruvate+NADH→Lactic Acid+NAD+

Alcoholic Fermentation

In this type of fermentation, pyruvate is first converted to acetaldehyde. Further, it is reduced to ethanol (alcohol) and carbon dioxide (CO₂).

• The reaction occurs mainly in yeast e.g., Saccharomyces cerevisiae.
• The main by-products are Ethanol and CO₂.
• Similar to lactic acid fermentation, there is regeneration of NAD+.
• This enables glycolysis to continue in anaerobic conditions.
• Example – Alcoholic fermentation is used in the production of alcoholic beverages like beer, or wines.
• Also used in bread-making, Kombucha tea, cider, and sake.

Anaerobic Fermentation vs. lactic Acid Fermentation

Both are types of fermentation that differ in the production of different by-products and the presence or absence of oxygen. Let us differentiate between both the fermentation types to understand them better.

Importance of Fermentation

Fermentation is useful for a variety of conditions. It is one of the oldest metabolic pathways that exist in prokaryotes and eukaryotes. Fermentation is commonly used across industries including food and beverage.

Let us discuss the importance of fermentation exploring its biological and industrial applications.

• Fermentation is used in food preservation, such as in making yoghurt, pickles, and sauerkraut.
• It helps extend the shelf life of the food products Buy inhibiting the growth of bacteria.
• Fermentation helps in the production of NAD + molecules which is important for the glycolysis process.
• Fermentation helps in the production of ATP in an environment where oxygen is not available.
• It also helps in providing of nutrients by breaking down complex molecules into simple ones.
• By the process of alcoholic fermentation the production of beer. wine or rum is possible.
• Ethanol being the by-product of alcoholic fermentation is also used in biofuel production.
• The fermentation process is used as an economical way of production of important products in pharmaceuticals as well.

FAQs on Fermentation: Anaerobic Respiration

What is fermentation in anaerobic respiration?

Fermentation is a process by which cells generate energy in the absence of oxygen. Hence, converting glucose into simpler molecules like lactic acid or ethanol while producing ATP.

What are the two main types of fermentation?

The two main types are lactic acid fermentation and alcoholic fermentation.

Which organisms use lactic acid fermentation?

Lactic acid fermentation occurs in certain bacteria, fungi, and animal muscle cells during intense exercise.

What is produced during alcoholic fermentation?

Alcoholic fermentation produces by-products in the form of ethanol (alcohol) and carbon dioxide (CO₂).

What are some common uses of fermentation in food production?

Fermentation is used to produce bread, yoghurt, cheese, beer, wine, and pickled vegetables.