Basic concepts of fermentation

Basic concepts of fermentation

The word fermentation is derived from the Latin word ‘fervere’ meaning to boil.  It was used to describe the boiling appearance of fruit juice or malted grain by the action of yeast due to the generation of carbon dioxide bubbles. In Biochemistry, fermentation means the generation of energy by the anaerobic catabolism of sugars. In industrial microbiology, Fermentation describe any process for the production of product by the mass culture of a microorganism and it includes both aerobic and anaerobic processes.

There are five major groups of commercially important fermentations:

1. Those that produce microbial cells (or biomass) as the product.
2. Those that produce microbial enzymes.
3. Those that produce microbial metabolites.
4. Those that produce recombinant products.
5. Those that modify a compound which is added to the fermentation for the transformation process.

1. Microbial biomass

The commercial production of microbial biomass may be divided into two major processes,

1. The production of yeast to be used in the baking 

2. The production of microbial cells to be used as human or animal food (single-cell protein). 

2. Microbial enzymes

Different types of microbial enzymes are produced in large quantities by fermentation techniques.   Even though enzymes may be obtained from plant and animal sources, microbial system possess high productivity and recombinant DNA technology has enabled the microbial synthesis of enzymes of animal origin.

3. Microbial metabolites

Metabolites are the intermediates and products of metabolism, typically characterized by small molecules with various functions.

Metabolites can be categorized into Primary metabolites and secondary metabolites.

Primary metabolites are made during the exponential phase of growth and the synthesis of primary metabolites are integral part of the normal growth process. Examples of primary metabolites are amino acids, nucleotides, vitamins, solvents, ethanol and organic acids. Secondary metabolites are organic compounds that are not directly involved in the normal growth, development or reproduction of an organism and generally produced during the stationary phase of growth.  Examples are antibiotics, pigments, toxins, etc. 

4. Recombinant products

The advent of recombinant DNA technology extended the range of potential fermentation products.  Genes from higher organisms may be introduced in to microbial cells so that the microbial cell will synthesize the 'foreign' or heterologous proteins. Microorganisms such as Escherichia coli, Saccharomyces cerevisiae and filamentous fungi are used to produce insulin, interferon, human serum albumin, factors VIII and IX, epidermal growth factor, calf chymosin and bovine somatostatin. 

5. Transformation processes

Microbial cells may be used to convert a compound to structurally related, financially more valuable compound.  Microorganisms can behave as chiral catalysts with high positional specificity and stereo specificity.  Thus microbial processes are more specific than chemical processes and enable the addition, removal or modification of functional groups at specific sites on a complex molecule. The reactions that could be catalyzed include dehydrogenation, oxidation, hydroxylation, dehydration and condensation, decarboxylation, amination, deamination and isomerization. Microbial processes operate at relatively low temperatures and pressures and do not need potentially polluting heavy-metal catalysts. Microbial transformation is used for the production of vinegar, steroids, antibiotics and prostaglandins.

Component parts of a fermentation Process

A fermentation process is divided into six basic component parts:

1. The formulation of media to be used in culturing the process organism during the development of the inoculum and in the production fermenter.
2. The sterilization of the medium, fermenters and ancillary equipments.
3. The production of an active, pure culture in sufficient quantity to inoculate the production vessel.
4. The growth of the organism in the production fermenter under optimum conditions for product formation.
5. The extraction of the product and its purification.
6. The disposal of effluents produced by the process.

Component parts of a fermentation Process

References

1. Principles of fermentation technology, PF Stanbury, A Whittakker, SJ Hall
2. Industrial microbiology –Casida L. E. J. R.