STEADY AND DYNAMIC SHEAR CHARACTERIZATION OF CELLULASE-PRODUCING TRICHODERMA-REESEI SUSPENSIONS

Suspension theology of fungal fermentations is important in determinat ion of mass transfer rates, as well as mixing quality. We have charact erized Trichorderma reesei RUT-C30 suspension theology during growth o n xylose (soluble) and cellulose (particulate) substrates, using both steady and dynamic shear measurements. Biomass growth was monophasic o n xylose and biphasic on cellulose; the latter behavior is consistent with relatively rapid, early growth on soluble sugars derived from rap idly hydrolyzed material, followed by a second, slower growth phase ow ing to hydrolysis of more recalcitrant cellulose by increasing cellula se concentrations. Steady shear measurements established the presence of a yield stress for fermentation broths when using a 10 (vol)% funga l inoculum. The Casson equation represented all data well. Casson para meters of viscosity and yield stress followed biomass evolution: two m axima in both parameters were observed with cellulose substrates, and a single maximum with xylose. Dynamic shear measurements on broths ind icated a gel behavior at small strains and a shear thinning liquid beh avior at larger displacements. These results indicate the need to incl ude theology and mixing considerations in the subsequent development o f a full biological and physical kinetic description of T. reesei cell ulose conversions.