Detailed B.Sc. Microbiology notes covering fermentation, industrial products, agricultural biotechnology, dairy biotechnology, genetic engineering applications and enzyme technology.
Fermentation is a biological process in which microorganisms or their enzymes convert suitable substrates into useful products under controlled conditions. In industrial microbiology, fermentation is used broadly to produce alcohols, organic acids, antibiotics, enzymes, vitamins, biomass and many other commercially valuable products.
Industrial fermentation does not always mean anaerobic metabolism. The term is commonly used for large-scale cultivation of microorganisms under controlled conditions, whether the desired process is aerobic or anaerobic.
The basic principle is to provide a suitable microorganism with an appropriate nutrient medium and controlled environmental conditions so that the organism grows or carries out a desired metabolic activity. The required product is subsequently recovered and purified.
Figure 1: General flow of an industrial fermentation process.
Solid-state fermentation involves growth of microorganisms on moist solid materials with little or no free-flowing water. Agricultural materials such as bran and other solid substrates can be used.
It is particularly useful for production of certain enzymes, organic acids and fermented agricultural products.
In submerged fermentation, microorganisms grow in a liquid nutrient medium. The culture is usually maintained in a fermentor with controlled temperature, pH, agitation and, where required, aeration.
It is widely used for industrial production of enzymes, antibiotics, organic acids and other microbial products.
A fermentor or bioreactor is a vessel designed to provide controlled conditions for the cultivation of microorganisms or cells and production of a desired biological product.
| Component | Function |
|---|---|
| Agitator | Mixes the culture medium and helps maintain uniform conditions. |
| Temperature control | Maintains the optimum temperature for the production organism. |
| pH control | Maintains the required pH during fermentation. |
| Aeration system | Provides oxygen for aerobic microorganisms. |
| Sampling port | Allows collection of culture samples for monitoring. |
| Foam control | Helps control excessive foam formation. |
| Exhaust system | Allows removal of gases generated during fermentation. |
Beer is a fermented beverage traditionally produced from cereal grains, particularly barley. The brewing process involves conversion of starch into fermentable sugars followed by alcoholic fermentation by yeast.
Yeasts of the genus Saccharomyces are central to beer fermentation. Depending on the brewing process, different brewing yeasts are used for different styles of beer.
Selected barley grains are allowed to germinate under controlled conditions. Germination promotes the development of enzymes that help break down starch and other components during subsequent processing. The grains are then dried to produce malt.
Malted grain is mixed with warm water. Enzymes present in the malt hydrolyze starch into fermentable sugars and produce a sugary liquid called wort.
The liquid portion is separated from the grain material. The wort is then boiled, and hops are commonly added. Boiling helps sterilize the wort, extracts hop components and prepares the medium for fermentation.
The wort is cooled to a suitable temperature before yeast is added. Cooling is important because excessive temperature can damage the fermenting yeast.
Brewing yeast converts fermentable sugars into ethanol and carbon dioxide. Various secondary metabolic products also contribute to the characteristic flavor and aroma of beer.
After primary fermentation, the beer is allowed to mature under controlled conditions. This period helps improve flavor and physical stability.
Yeast cells and suspended materials are removed or reduced by suitable clarification methods. The resulting beverage becomes clearer.
The finished beer is packaged in suitable containers under hygienic conditions.
Figure 2: Picture-style flowchart of major steps in beer production.
“Describe the production of beer with a suitable flowchart.”
For a 10-mark answer, include definition, raw materials, microorganism, malting, mashing, wort preparation, hopping, cooling, fermentation, maturation, clarification, packaging and the complete flowchart.
Ethanol is an important industrial product produced by microbial fermentation of sugar-containing or starch-containing raw materials. Yeasts, particularly members of the genus Saccharomyces, are widely used for alcoholic fermentation.
During alcoholic fermentation, yeast converts fermentable sugars mainly into ethanol and carbon dioxide under oxygen-limited conditions. The general reaction can be represented as:
The carbohydrate-containing raw material is prepared to provide a suitable substrate for microbial fermentation.
When starch-rich raw materials are used, starch must first be converted into fermentable sugars through enzymatic hydrolysis.
A suitable active yeast culture is introduced into the prepared fermentation medium.
The yeast metabolizes fermentable sugars and produces ethanol and carbon dioxide.
The fermented broth contains ethanol along with water, cells and other components. Distillation is used to concentrate ethanol.
Further processing may be used depending on the required purity and intended use of the ethanol.
Figure 3: Picture-style flowchart of industrial ethanol production.
“Describe industrial production of ethanol by microbial fermentation with a suitable flowchart.”
Acetic acid is an important organic acid used in food preservation, chemical industries and the production of vinegar. Microorganisms of the genus Acetobacter are important in the biological oxidation of ethanol to acetic acid under aerobic conditions.
Species of Acetobacter are commonly associated with vinegar production. These bacteria are aerobic and oxidize ethanol to acetic acid.
The essential principle is the aerobic oxidation of ethanol to acetic acid.
Figure 4: Picture-style flowchart showing microbial production of acetic acid.
“Describe industrial production of acetic acid by microorganisms.”
Agricultural microbial biotechnology involves the use of microorganisms, microbial products and biological techniques to improve agricultural productivity, soil fertility, plant propagation and crop health.
Biofertilizers are preparations containing living microorganisms that improve nutrient availability or soil fertility when applied to soil, seeds or plants.
Composting is the controlled biological decomposition of organic waste by microorganisms to produce a relatively stable organic material that can be used as a soil amendment.
Plant tissue culture is the cultivation of plant cells, tissues or organs under sterile conditions on a suitable artificial nutrient medium. It is based on the concept of cellular totipotency, which is the ability of a plant cell under appropriate conditions to regenerate into a complete plant.
Micropropagation is the rapid multiplication of plants using tissue culture techniques. It allows production of large numbers of genetically similar plants from a small amount of starting plant material.
Figure 5: Picture-style flowchart of plant micropropagation.
Cell fusion is the process in which two cells are induced to fuse and form a single hybrid cell. In plant biotechnology, fusion of protoplasts can produce hybrid cells containing genetic material from different parental cells.
Embryo transfer is a reproductive biotechnology technique in which an embryo is transferred from a donor female to a suitable recipient female after appropriate preparation. It is used in animal breeding and reproductive biotechnology to increase the number of offspring obtained from genetically valuable females.
Dairy biotechnology involves the use of microorganisms, enzymes and controlled biological processes in the production and preservation of milk and milk products. Microorganisms are particularly important in fermented dairy products such as yogurt and certain types of cheese.
Milk is a nutrient-rich biological fluid containing water, proteins, fat, lactose, minerals and vitamins. Because milk provides an excellent medium for microbial growth, proper processing and storage are essential for maintaining its quality and safety.
Cheese is a concentrated dairy product obtained by coagulating milk proteins and separating the resulting curd from whey, followed by additional processing such as salting, pressing and, depending on the type, ripening.
The basic principle of cheese production is the coagulation of milk proteins, particularly casein, followed by separation of curd and whey. Microorganisms and enzymes may contribute to acid development, flavor formation and ripening depending on the cheese variety.
Lactic acid bacteria are commonly used as starter cultures in cheese manufacture. The exact organisms depend on the type of cheese and production method. Ripening may involve additional bacteria, yeasts or molds in selected varieties.
Good-quality milk is selected and processed under hygienic conditions. The milk may be standardized and heat treated depending on the type of cheese being produced.
Selected microorganisms are added to develop acidity and contribute to the characteristic properties of the cheese.
Milk is coagulated through enzymatic action, acidification or a combination of processes. The casein network traps much of the milk's fat and water, producing a gel-like curd.
The curd is cut into pieces. Cutting increases the surface area from which whey can be released.
The liquid whey is separated from the solid curd. Further processing of the curd depends on the desired cheese variety.
Salt may be added directly to the curd or applied by other methods. Salting contributes to flavor and influences microbial activity and moisture.
The curd may be pressed to remove additional whey and obtain the desired shape and texture.
Selected cheeses are ripened under controlled conditions. Microbial and enzymatic reactions during ripening contribute to the characteristic flavor, aroma and texture.
Figure 6: Picture-style flowchart of cheese production.
“Describe the production of cheese with suitable flowchart and mention the role of microorganisms.”
Yogurt is a fermented milk product produced through the controlled fermentation of lactose by selected lactic acid bacteria. The acid produced during fermentation lowers the pH and causes changes in milk proteins, producing the characteristic texture and sour taste.
Traditional yogurt production commonly uses a symbiotic starter culture containing Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus.
The starter organisms metabolize lactose and produce lactic acid. Increasing acidity lowers the pH of milk and causes casein proteins to coagulate, producing the characteristic yogurt gel.
Good-quality milk is selected and its composition may be adjusted according to the desired yogurt characteristics.
Milk is subjected to an appropriate heat treatment. This reduces undesirable microorganisms and modifies milk proteins in a way that supports the desired texture of yogurt.
Homogenization reduces the size of fat globules and helps produce a uniform product with desirable texture.
The treated milk is cooled to a temperature suitable for the starter culture.
The yogurt starter culture is added to the prepared milk under hygienic conditions.
The inoculated milk is incubated under suitable conditions. The bacteria multiply and ferment lactose, producing lactic acid.
As lactic acid accumulates, the pH decreases and casein undergoes acid-induced coagulation, producing the characteristic yogurt structure.
After the desired acidity and texture are achieved, the yogurt is cooled to slow further microbial activity and stored under suitable conditions.
Figure 7: Picture-style flowchart of yogurt production.
“Describe the production of yogurt and explain the role of starter cultures.”
Sour milk is produced when lactic acid bacteria ferment lactose in milk, leading to accumulation of lactic acid and reduction of pH. The increased acidity produces a characteristic sour taste and may cause protein coagulation.
Lactic acid bacteria are responsible for the conversion of lactose into lactic acid. Depending on the product, different starter cultures may be used.
Ice cream is a frozen dairy product containing milk components, fat, sugar and other permitted ingredients. Its manufacture involves formulation, pasteurization, homogenization, cooling, aging, freezing and hardening.
Skimmed milk is milk from which most of the milk fat has been removed. It retains many of the water-soluble components of milk while having a much lower fat content than whole milk.
Dry milk powder is produced by removing most of the water from milk. Drying increases shelf life and reduces the water available for microbial growth.
Pasteurization is a controlled heat treatment used to reduce pathogenic and spoilage microorganisms in milk while causing relatively limited changes to the quality of the product.
| Method | General description |
|---|---|
| Batch / Holder method | Milk is held at a suitable pasteurization temperature for a specified period. |
| HTST | Milk is heated at a higher temperature for a short time and then rapidly cooled. |
| UHT | Milk is exposed to very high temperature for a very short period and processed under appropriate hygienic conditions. |
Enzyme technology is the application of enzymes in industrial, biotechnological, food, pharmaceutical and other processes. Enzymes are biological catalysts that accelerate biochemical reactions without being consumed in the overall reaction.
Microorganisms are widely used for industrial enzyme production because they grow rapidly, can be cultivated on relatively inexpensive substrates, and can often produce large quantities of enzymes under controlled conditions. Production can be scaled up in fermentors.
Figure 8: General flowchart of microbial enzyme production.
Proteases are enzymes that hydrolyze peptide bonds in proteins and produce smaller peptides and amino acids. Microbial proteases are widely used in detergent, food, leather, pharmaceutical and other industries.
Proteases are produced by various bacteria and fungi. Species of Bacillus and several filamentous fungi are important industrial sources.
Amylases are enzymes that hydrolyze starch into smaller carbohydrates. They are important industrial enzymes used in food, fermentation, textile, paper and other industries.
Amylases are produced by several bacteria and fungi. Species of Bacillus and Aspergillus are important microbial sources.
Figure 9: Picture-style flowchart of microbial amylase production.
Chitinases are enzymes that hydrolyze chitin, a structural polysaccharide found in the exoskeletons of many arthropods and in fungal cell walls. Microbial chitinases have applications in biotechnology, agriculture and environmental processes.
Various bacteria and fungi can produce chitinases, particularly when chitin-containing materials are present as substrates or inducers.
Pectinases are enzymes that degrade pectin, a structural polysaccharide found in plant tissues. They are important in fruit processing and several other industrial applications.
Pectinases are produced by several fungi and bacteria. Species of Aspergillus are important sources of industrial pectinolytic enzymes.
Figure 10: Picture-style flowchart of microbial pectinase production.
| Field | Applications |
|---|---|
| Medical biotechnology | Vaccines, therapeutic proteins, diagnostics and molecular medicine. |
| Industrial biotechnology | Production of enzymes, organic acids, alcohols and other microbial products. |
| Agricultural biotechnology | Biofertilizers, tissue culture, crop improvement and disease management. |
| Food biotechnology | Fermented foods, dairy products, beverages and food enzymes. |
| Environmental biotechnology | Waste treatment, biodegradation and bioremediation. |
| Genetic engineering | Gene cloning, recombinant DNA technology and production of recombinant products. |