Viscous Fermentation Products

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Abstract
The viscous nature of fermentation broths has a marked effect on many parameters and process conditions within the bioreactor, often resulting in changes in microbial behavior and product formation. Although fermentation processes that involve significant changes in broth rheology have attracted much research interest, significant problems still remain. Particular difficulties remain in relation to processes where the broth develops pronounced non-Newtonian characteristics. This article reviews some of the models developed to describe these fermentation fluids and their limitations; the bioreactor types employed and their mode of operation; the problems encountered because of the nature of the fluids, for example, monitoring and control; and the gradients found in such systems. To illustrate the above, four specific processes are described in detail — the production of filamentous biomass (SCP) and three extracellular microbial polysaccharides, xanthan, pullulan, and scleroglucan.