POLYSACCHARIDE PRODUCTION BY AUREOBASIDIUM-PULLULANS .3. THE INFLUENCE OF INITIAL SUCROSE CONCENTRATION ON BATCH KINETICS

The kinetic parameters for a 7 day polysaccharide fermentation by Aureobasidium pullulans (NRRL 6220) in shake flasks with 2.5, 5, 10 and 20% initial sucrose concentrations were calculated by applying the Logistic, the Luedeking-Piret and the modified Luedeking-Piret equations for biomass and polysaccharide formation and for sucrose consumption respectively. All three models provided good describtion of the fermentation in the range of initial sucrose concentration tested. The specific growth rate (mu), the maximum attainable biomass (X(max)) and the specific substrate consumption rate ([dS/dt]/X) were influenced by the initial sucrose concentration showing peak values for mu at 10% and for X(max) and ([dS/dt]/X) at 5% sucrose concentration. While the specific production rate ([dP/dt]/X) was not affected much by the initial sucrose, the growth associated product (P-m) and the non-growth associated product (P-n) were, and the former was consistently much higher than the latter. Conversely, growth associated substrate consumption (S-x) was higher than non-growth associated substrate consumption (S-beta) at initial sucrose concentrations up to 10%. Calculation of the fraction of sucrose consumed and the fraction of polysaccharide produced during the growth and non-growth phases at the seventh day of the fermentation suggested that more energy is consumed for maintenance at higher initial sucrose concentrations. An efficient production process could possibly be obtained in a fermentation of a shorter duration operated in a sucrose fed-batch mode with 5% sucrose as the starting concentration.