RHEOLOGY OF FILAMENTOUS FERMENTATIONS

The performance of a bioreactor containing a filamentous fermentation broth is greatly influenced by the rheological properties of the broth . These properties are determined mainly by the concentration of bioma ss, its growth rate and morphology. Included in the morphology are suc h factors as the geometry of hyphae (length, diameter, branching frequ ency), hyphal flexibility and hyphal-hyphal interactions, which can al l be affected by the operational design of the reactor. Thus, correlat ions describing viscosity as a function of biomass only are of limited value. A better understanding of the relations between morphology and rheology may be achieved by a combination of rheological and morpholo gical studies. Rheological properties are normally determined using of f-line measurements in-spite of associated problems with sample treatm ent influencing the results. Equipment for dynamic, on-line, measureme nt of morphology and rheology is available, but little used in filamen tous fermentations. Controlling the rheological properties of mycelial fermentations may be difficult because of the great number of factors influencing mycelial development and/or hyphal-hyphal interactions. P olymer solutions are often used to simulate flow behaviour of filament ous fermentations and scale-up and mass transfer considerations are ba sed on these studies. Although much information has been gained this w ay, the predictions developed do not include the effect of an active b iomass on the mass transfer and flow properties of the culture. It is important to carry out studies on the non-homogeneous fermentation flu ids, and develop correlations based on these studies.