Influence of oxygen tension, biomass concentration, and specific growth rate on the rheological properties of a filamentous fermentation broth.

The influence of oxygen tension, biomass concentration, and specific growth rate on the rheological properties of an Aspergillus niger fermentation broth was investigated by growing the fungus in continuous culture. The rheological properties were measured on-line using an impeller rheometer system. The effect of the specific growth rate on broth rheology was strongly influenced by the dissolved oxygen, (DO) concentration in the broth. At DO concentrations above 10% of saturation, K increased with the dilution rate, and at DO concentrations below 10% of saturation, K decreased with increasing dilution rate. The largest influence of a change in the DO concentration on the viscosity of the broth was found at the lowest growth rates and the lowest DO concentrations. K/x, a term that gives a simple description of the structure or the morphology of the culture, was found to increase with biomass concentration.