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In fermentation or bioprocessing, microbial/enzymic or biochemical reactions need appropriate designing of the medium in which reactions occur.
Many technological concerns are involved in medium design engineering (Fig. 3.1) in bioprocessing.
For fermentative processing this need is to establish the most economic medium for any particular fermentation taking care of certain basic requirements to be met by any nutritional medium.
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The medium design engineering for fermentation should take care of:
(a) Source of energy
(b) Source of carbon
(c) Source of nitrogen
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(d) Source of minerals and
(e) Source of growth factors in relation to technological concerns.
On the other hand bio-catalytic medium engineering takes care of micro environments consisting of a thin layer of water around the biocatalyst and an interfacial region, which forms the transition between the bio-catalytic and continuous phases.
In recent years an increasing important development in the field of synthetic bioinorganic and bioorganic chemistry relates to application of biocatalysts to chemical reactions. This is not surprising. Biocatalysts are known to perform catalysis very effectively a wide variety of organic and inorganic reactions under relatively mild conditions in a stereo and/or regio-selective way.
So medium design engineering has many concerns. One of the most important concerns is optimization of a fermentation process in the design of the growth and production medium. Besides meeting nutritional and environmental requirements of the fermenting microorganism, the medium must also minimize several techno economic constraints.
Basic Concept in Medium Design:
Fermentation:
In meeting nutritional and environmental requirements the first approximation is the minimal medium design, minimal medium design is based on the simple stoichiometry for growth and products formation as given below.
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C-source + N-source + O2 + Minerals + Growth factors/Specific nutrients → Cell biomass + Product + C02 + 2H2O + Q cals
The basic concept in such design is simply a material balance and energy balance.
Chemical Reactions in Biological Fashion:
In chemical reactions like bioorganic synthesis or bioinorganic transformations, medium engineering concerns designing microenvironments for the biocatalyst. The basic objective of this is to reach maximal activity, stability and productivity.
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Reactant substrate containing liquid medium + Biocatalyst Surrounded by Microenvironments Products + Co-products + Biocatalysts if any
Medium design engineering in such systems, therefore, involves aspects such as stabilizing the essential liquid layer around the biocatalyst, controlling electrostatic and hydrophobic interactions between substrate(s) and biocatalyst.
