Evaluation of medium composition and fermentation parameters on pullulan production by Aureobasidium pullulans.

The goal of this study was to enhance pullulan production by evaluating the effects of different fermentation parameters. Various carbon sources and their concentrations, yeast extract (YE) concentrations, fermentation temperatures and various pH profiles were examined. The optimal growth condition for pullulan production by Aureobasidium pullulans has been found as 75 g/L of sucrose as carbon source, 3 g/L of YE and cultivation temperature at 30 (°)C. Under these conditions with an initial pH at 5, 20.7 g/L of final pullulan concentration and 0.22 g/L/h maximum production rate were obtained. Later on, various pH profiles, agitation speeds, aerations and fed-batch fermentation were evaluated. The results demonstrated that pullulan production was enhanced to 25.8 g/L after 7-day cultivation with a 0.68 -g/L/h maximum production rate. There was no significant improvement of pullulan production from fed-batch fermentation. The optimal kinetics parameters were as follows: initial pH at 2.0, switched to pH 5.0 after 72 h and kept constant; agitation speed at 200 rpm; aeration at 1.5 vvm. The quality analysis demonstrated that the pullulan content produced from optimal conditions was 94.5% and its viscosity was 2.3 centipoise (cP). Fourier transform infrared spectroscopy also suggested that pullulan dominated the produced exopolysaccharide.