The microbial fermentation process has become an integral part of the recent
advances in genetic engineering and biotechnology. Most of the fermentation processes
are complex processes that involve multiple substrate, gas-liquid mass transfer, and
sometimes nowNewtonian broth rheology. The final desired product concentration in
the aqueous medium can vary over a wide range. Some of the organic acid fermentations
such as citric acid and glutamic acid, a concentration of 100 grams per liter or
above can be achieved. On the other hand, some more complex macromolecular
product fermentations, such as vitamin B,, and human insulin, a concentration of 1 gram per liter or less is satisfactory because these products command premium prices.
As shown in FIGURE1, the fermentation product cost is more or less dictated by the
final product concentration in the fermentation broth. It is always desirable to increase the final product concentration in the fermentation broth. The primary causes of the dilute nature of the fermentation end product are that the product itself can stop its own synthesis (product regulation) and product degradation in the fermenting broth. Even though these effects that occur at high product concentration are known,
approaches for major improvement have been primarily limited to genetic manipulation.
By means of random mutation and selection, strains tolerant to a high concentration
of product may be selected to avoid such problems.