Range of fermentation processes

Dr.Jitender Kumar

Department of Biotechnology

HMV,Jalandhar

​

MICROBIAL BIOMASS�

• The commercial production of microbial biomass may be divided into two major processes
• The production of yeast to be used in the baking industry
• Production of microbial cells to be used as human food or animal feed (single-cell protein).

History of baker yeast

• Bakers’ yeast has been produced on a large scale since early 1900s and yeast was produced as human food in Germany during the First World War.
• However, it was not until the 1960s that the production of microbial biomass as a source of food protein was explored to any great depth by microbiologist.

MICROBIAL BIOMASS�

​

• Few large-scale continuous processes for animal feed production were established in the 1970s. These processes were based on hydrocarbon feedstocks,which could not compete against other high protein animal feeds, resulting in their closure in the late 1980s.
• However, the demise of the animal feed biomass fermentation was developed for the production of fungal biomass for human food.
• This process was based on a more stable economic platform and has been a significant economic success

​

Microbial enzymes

• Enzymes have been produced commercially from plant, animal, and microbial sources.
• However, microbial enzymes have the enormous advantage of being able to be produced in large quantities by established fermentation techniques.
• Also, it is infinitely easier to improve the productivity of a microbial system compared with a plant or an animal cell culture.

Microbial enzymes

• Furthermore, the advent of recombinant DNA technology has enabled enzymes of animal origin to be synthesized by microorganisms
• Recombinant DNA technology from which it may be seen that the majority of applications are in the food and related industries.

• Enzyme production is closely controlled in microorganisms
• and in order to improve productivity these controls may have to be exploited or
• modified. Such control systems as induction may be exploited by including inducers
• in the medium (see Chapter 4), whereas repression control may be removed by
• mutation and recombination techniques. Also, the number of gene copies coding for
• the enzyme may be increased by recombinant DNA techniques. Aspects of strain
• improvement are discussed in Chapter 3.

​

MICROBIAL METABOLITES�

• The growth of a microbial culture can be divided into a number of stages
• After the inoculation of a culture into a nutrient medium there is

a period during which growth does not appear to occur; this period is referred as the lag phase and may be considered as a time of adaptation.

• Following a period during which the growth rate of the cells gradually increases, the cells grow at a constant maximum rate and this period is known as the log, or exponential, phase.
• Eventually after log phase growth ceases and the cells enter the so-called stationary phase

​

RECOMBINANT PRODUCTS�

• The advent of recombinant DNA technology has extended the range of potential fermentation products.
• Genes from higher organisms may be introduced into microbial

cells such that the recipients are capable of synthesizing “foreign” proteins.These proteins are described as “heterologous” meaning “derived from a different organism.”

• A wide range of microbial cells has been used as hosts for such systems including Escherichia coli, Saccharomyces cerevisiae, and filamentous fungi.
• Animal cells cultured in fermentation systems are also widely used for the production of heterologous proteins

Genetically engineered organisms

• Although the animal cell processes were based on microbial fermentation technology, a number of novel problems had to be solved—animal cells were considered extremely fragile compared with microbial cells.
• The achievable cell density is very much less than in a microbial process and the media are very complex.
• Products produced by such genetically engineered organisms include interferon, insulin, human serum
• albumin, factors VIII and IX, epidermal growth factor, calf chymosin, and bovine somatostatin.

Gene Transfer

• Important factors in the design of these processes include the secretion of the product, minimization of the degradation of the product, and control of the onset of synthesis during the fermentation, as well as maximizing the expression of the foreign gene.

​

TRANSFORMATION PROCESSES�

• Microbial cells may be used to convert a compound into a structurally related, financially more valuable, compound.
• Because microorganisms can behave as chiral catalysts

with high positional specificity and stereo specificity, microbial processes are more specific than purely chemical ones and enable the addition, removal, or modification of functional groups at specific sites on a complex molecule without the use of chemical protection.

Biotransformation

• The reactions, which may be catalyzed include dehydrogenation,

oxidation, hydroxylation, dehydration and condensation, decarboxylation, animation, deamination, and isomerization.

• Microbial processes have the additional advantage over chemical reagents of operating at relatively low temperatures and pressures

without the requirement for potentially polluting heavy-metal catalysts.

• Although the production of vinegar is the oldest established microbial transformation process (conversion of ethanol to acetic acid), the majority of these processes involve the production
• of high-value compounds including steroids, antibiotics, and prostaglandins

​

References

• Stanbury, P.F., Whitaker, A. and Hall, S.J. (2001), Principles of Fermentation Technology 2nd ed., Pergamon Press, Oxford.
• Young, M.Y. (2000), Comprehensive Biotechnology (Vol. 1-4), Pergamon Press, Oxford.
• Young, M.Y. (1996), Environmental Biotechnology, Principles & Applications, Kluwer
• S.J. Pirt (1985), Principles of microbes and cell cultivations. Blackwell Scientific Publication, London.

​

References

• Biotechnology: Expanding Horizon – B.D. Singh (Kalyani Publication)
• Biophysical and Biochemical Technology – Wilson and Walker (Cambridge University Press)
• Principle of Gene Manipulation and Genomics – Primrose (Blackwell Publication)
• General Microbiology – R.P. Singh (Kalyani Publication)
• General Microbiology – R.Y. Stanier
• Animal Cell Culture and Technology – Michael Butler

​

​

​

​

​

Thanks