What is Microbial Fermentation and How It Works with 10 + Examples

 Microbial Fermentation Definition, History, Types and Examples

Microbial Fermentation is a process in which complex substances are converted into simple substances with the help of microorganisms such as Bacteria, Yeast and Others.

Microbial Fermentation Definition: 

  • Microbial fermentation is a chemical reaction in which the breakdown of nutrients, mostly sugars and carbohydrates, by microbes in the absence of oxygen.

  • Microbial fermentation is a biochemical process in which small organisms break down sugars and carbohydrates using special enzymes, without needing oxygen.
What is Microbial Fermentation and How It Works with Examples

What is Microbial Fermentation?

Microbial Fermentation is a biochemical process where complex organic substances are transformed into simpler substances by bacteria, yeasts, and other microorganisms. The term "fermentation" comes from the Latin word "fervere," meaning to boil. The study of fermentation is called Zymology.

Louis Pasteur, a French chemist and microbiologist, coined the term "fermentation" in 1857. He demonstrated that microorganisms like bacteria and yeast can cause fermentation. Pasteur showed that yeast converts glucose into ethanol, making him known as the father of fermentation.

Fermentation takes place in special vessels called fermenters or bioreactors, which provide a controlled environment for microbial growth and product formation. Different types of bioreactors include Continuous Stirred Tank Bioreactors, Bubble Column Bioreactors, Airlift Bioreactors, Fluidized Bed Bioreactors, and Packed Bed Bioreactors.

There are various types of fermentation based on the media used, type of fermenter, and end product desired. Fermentation is used in the production of alcoholic beverages like beer and wine, as well as in making ethanol, bread, yogurt, vinegar, kombucha, acetic acid, citric acid, gluconic acid, antibiotics, vitamins (such as B12 and B2), enzymes, and more.

History of Microbial Fermentation: 

The history of fermentation spans thousands of years, with humans using microbial fermentation to produce food and drinks. The understanding of fermentation evolved over time:

In 1680, Leeuwenhoek observed intact yeast cells for the first time.
In 1854, Louis Pasteur discovered that yeast fermentation causes alcohol production.
In 1897, Bischner discovered that various yeast enzymes are responsible for carbohydrate fermentation.

The development of pure culture technology marked a turning point, shifting from natural to controlled fermentation, and heralding the era of modern fermentation technology.

Microbial Fermentation Examples: 

Following are the examples that highlight the versatility of microbial fermentation in producing a wide range of valuable products, from food additives to pharmaceuticals and industrial enzymes.
  • Yogurt Production: Lactic acid bacteria ferment lactose in milk to produce lactic acid, giving yogurt its tangy flavor and texture.
  • Beer Brewing: Yeast fermentation of malted barley sugars produces alcohol and carbon dioxide, giving beer its alcoholic content and bubbles.
  • Wine Making: Yeast fermentation of grape sugars produces alcohol, transforming grape juice into wine.
  • Vinegar Production: Acetobacter bacteria ferment ethanol in wine or cider into acetic acid, producing vinegar.
  • Antibiotic Production: Microbial fermentation is used to produce antibiotics like penicillin, where fungi or bacteria are cultured to synthesize these compounds for medical use.
  • Vaccine Production: Many vaccines, such as those for hepatitis B and some influenza vaccines, are produced using microbial fermentation. For instance, recombinant DNA technology can be employed to introduce genes encoding specific antigens into microbial hosts like yeast or bacteria, which then produce the desired antigens used in vaccines.
  • Xanthan Gum Production: Xanthan gum, a commonly used food additive and thickening agent, is produced through fermentation by the bacterium Xanthomonas campestris. The bacteria ferment carbohydrates (like glucose or sucrose) to produce xanthan gum, which is then purified for commercial use.
  • Vitamin Production: Various vitamins such as riboflavin (vitamin B2), vitamin C, and vitamin B12 are produced through microbial fermentation. For instance, certain strains of bacteria or fungi are cultured under controlled conditions to synthesize these vitamins, which are then harvested for use in food fortification or supplements.
  • Lysine Production: Lysine, an essential amino acid used in animal feed and food production, is produced by fermentation using bacteria like Corynebacterium glutamicum. These bacteria convert sugars into lysine through a series of enzymatic reactions.
  • Protease Production: Proteases are enzymes that break down proteins into smaller peptides or amino acids. Many proteases used in industrial processes (e.g., in detergents, food processing) are produced via microbial fermentation. Bacteria or fungi capable of producing proteases are cultivated and the enzymes are extracted and purified for commercial use.

Types of Microbial Fermentation

There are several types of Microbial fermentation, based on Media, type of fermenter, and type of end products. These fermentation types will be explained below. Check out!

  1. Based on Media / Substrates, there are two types of fermentation solid-state fermentation and Submerged fermentation. 
  2. Based on the type of fermenter, there are two types of fermentation Batch fermentation and continuous fermentation.
  3. Based on the end product, fermentation is of two types Aerobic fermentation and Anaerobic fermentation (Alcoholic/ethanol fermentation & Lactic acid fermentation).
Types of microbial fermentation
Image Source: researchgate.net

Based on Media or Substrates:

1. Solid State Fermentation (SSF):
Solid-state fermentation involves cultivating microorganisms on a solid substrate with low moisture content. This method is used in various industries such as food, pharmaceuticals, cosmetics, fuel, and textiles. Common solid substrates used include plant and animal materials, cereal grains (like corn, rice, wheat, and barley), legume seeds, straws, and sawdust. SSF is often used in producing bakery products like bread and in cheese maturation. It offers advantages such as higher yields, productivity, and cost-effectiveness, as well as reduced protein breakdown.

2. Submerged Fermentation (SMF):
Submerged fermentation is an anaerobic process where microorganisms are inoculated into a liquid medium to produce biomolecules. The substrate used is always in a liquid state and provides all necessary nutrients for microbial growth. Types of SMF include batch fermentation, continuous fermentation, fed-batch fermentation, and perfusion batch culture. Examples of products produced through SMF include citric acid, biological detergents, starch hydrolysates, cheese, and wine.

Based on the Type of Fermenter or Bioreactor:

1. Batch Fermentation:
In batch fermentation, raw materials and seed material are loaded into the apparatus at once. The fermentation process occurs for a specific period, after which the resulting liquid is removed from the apparatus. Batch fermentation is valuable for producing antibiotics, enzymes, and other valuable products from microorganisms.

2. Continuous Fermentation:
Continuous fermentation involves continuously feeding fresh nutrients into the culture while simultaneously removing the same volume of cell suspension. This type of fermentation can be conducted in a reactor with a constant nutrient feed rate. Although less common in industry due to challenges like maintaining sterile conditions over time, continuous fermentation is used in applications like wastewater treatment, brewing, and insulin production.

Based on End Product Fermentation Types:

1. Aerobic Fermentation:
Aerobic fermentation occurs in the presence of oxygen and nutrients, where organic matter is assimilated by microorganisms. Glucose is completely broken down into carbon dioxide and oxygen, mainly within mitochondria and cell cytoplasm.

2. Anaerobic Fermentation:
Anaerobic fermentation extracts energy from carbohydrates in the absence of oxygen. This process starts with glycolysis, leading to the production of ATP molecules. Types of anaerobic fermentation include ethanol fermentation (used in alcoholic beverage production) and lactic acid fermentation (used in yogurt and fermented milk production).

3. Alcoholic Fermentation:
Alcoholic fermentation is a biochemical process where sugar molecules are converted into alcohol and carbon dioxide by yeast. This process is essential for producing alcoholic beverages like wine and beer.

4. Lactic Acid Fermentation:
Lactic acid fermentation converts sugar molecules into lactic acid using bacteria like Lactobacillus. This process is used in yogurt and fermented milk production. During lactic acid fermentation, NAD+ is reduced to form NADH, which produces ATP molecules for cellular energy.

Process of Microbial Fermentation

Fermentation is a crucial process that occurs in a bioreactor, which is typically a closed cylinder where a nutrient medium is mixed with microorganisms. Air, sometimes oxygen-saturated, is pumped through to provide necessary oxygen. The temperature is controlled using water or steam circulating through heat exchanger tubes. The bioreactor design allows for precise control of growth conditions including temperature, pH (acidity or alkalinity), and dissolved oxygen concentration.

The steps involved in fermentation include:
  • Preparation of Culture Medium: The culture medium provides organic carbon and essential nutrients (like nitrogen, phosphorus, and other elements) for microbial growth. It must be sterilized to eliminate foreign microorganisms, typically done using heat, radiation, filtration, or chemicals.
  • Obtaining Pure Microbial Strains: Before fermentation begins, pure and highly productive microbial cultures are obtained and stored under controlled conditions to maintain viability and prevent contamination.
  • Actual Fermentation Process: Fermentation encompasses the entire biotechnological process from introducing microbes into a prepared and heated medium to the completion of biosynthesis. This process occurs in the fermenter, where microbes convert nutrients into desired products or grow. The resulting mixture of microbes, nutrients, and biosynthetic products is called culture liquid or broth.
  • Isolation and Purification of Final Product: After fermentation, the desired product is isolated and purified from other components of the culture broth. Techniques such as filtration, centrifugation (separation of particles by centrifugal force), and chemical precipitation are used to separate and purify the target product.
Overall, fermentation involves careful preparation of culture medium, the introduction of pure microbial strains, controlled biosynthesis in a bioreactor, and subsequent purification of the final product for various industrial applications. This process is essential in biotechnology for producing valuable substances like enzymes, antibiotics, vitamins, and biofuels.

What is a Bioreactor:

A fermentation bioreactor, also known as a fermenter, is a specialized vessel used for the fermentation process in industries like beverages, chemicals, food, dairy, brewing, and pharmaceuticals. This vessel creates a controlled environment that supports microbial growth and product formation.

Key components of a fermentation tank include:
  • Tank Body: This is where various bacteria are cultivated and fermented. It's designed with good sealing to prevent contamination.
  • Stirring System: A stirring slurry continuously mixes the contents during fermentation.
  • Aeration System: The bottom of the tank has a sparger that introduces air or oxygen needed for bacterial growth.
  • Control Sensors: Sensors like pH electrodes and dissolved oxygen (DO) electrodes are mounted on the top plate to monitor changes in pH and oxygen levels during fermentation.
  • Controller: This device displays and regulates fermentation conditions.
Fermentation tanks can be classified based on equipment type (mechanical stirring and ventilation vs. non-mechanical stirring and ventilation) and microbial metabolism (aerobic vs. anaerobic fermentation). These tanks play a crucial role in ensuring optimal conditions for microbial activity, which is essential for producing various products through fermentation processes.

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