CORRELATION OF ASPERGILLUS-NIGER BROTH RHEOLOGICAL PROPERTIES WITH BIOMASS CONCENTRATION AND THE SHAPE OF MYCELIAL AGGREGATES

Aspergillus niger was grown in a 7-L chemostat at biomass levels of 7 to 9 gL-1; dilution rates of 0.03, 0.05, 0.075, and 0.009 h-1; and dis solved oxygen tensions of 7%, 12%, and 40% of air saturation. Broth rh eological measurements were made on-line, while off-line image analysi s was used to measure mycelial morphology, including characterization of mycelial aggregates (clumps). Under all conditions, more than 87% o f the hyphae were in clumps, the shape of which determined the rheolog ical characteristics of the broth. In particular, the power law consis tency index could be correlated with the biomass concentration and the roughness factor of the clumps, which describes their hairiness. A de crease in specific growth rate decreased roughness, possibly due to ch anges in the amount of clump breakup. However, decreases of roughness with increasing dissolved oxygen tension might rather imply some effec t on hyphal-hyphal interactions within the clumps. (C) 1993 John Wiley & Sons, Inc.