Comparison of pullulan production performances of air-lift and bubble column bioreactors and optimization of process parameters in air-lift bioreactor

• It is the first report for pullulan production in air-lift bioreactor by using statistical optimization method.
• Effective pullulan production as compared to previous studies related to pullulan production in stirred tank bioreactors.
• Comparison of two pneumatically agitated bioreactors.

The production of pullulan from synthetic medium by Aureobasidium pullulans DSM-2404 in air-lift and bubble column bioreactors was investigated. The kinetics of polysaccharide, pullulan and biomass production were determined. Maximum effective yield (g pullulan produced g−1 initial sugar) obtained in air-lift bioreactor (YP/S = 0.402) was found to be higher than that obtained in bubble column bioreactor (YP/S = 0.342). Response surface methodology was used to investigate the effects of three factors (initial sugar concentration, aeration rate and incubation time) on the concentration of pullulan in air-lift bioreactor for batch cultures of A. pullulans. No previous work has used statistical analysis in determining the interactions among these variables in pullulan production in an air-lift bioreactor. Results of the statistical analysis showed that the fit of the model was good in all cases. Initial sugar concentration, aeration rate and incubation time had a strong linear effect on pullulan concentration. Moreover, pullulan concentration was significantly influenced by the negative quadratic effects of the given variables and by their positive or negative interactions except the interaction between initial sugar concentration and incubation time (P > 0.05). Maximum pullulan concentration of 38.77 g/L was obtained at the optimum levels of process variables (initial sugar concentration 95.2 g/L, aeration rate 1.93 vvm and incubation time 5.36 days)

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