Experimental modeling and optimization of pullulan production by Aureobasidium pullulans AZ-6

The objective of this study was to optimize the fermentation parameters by using response surface methodology for increasing pullulan production of Aureobasidium pullulans AZ-6 in synthetic fermentation medium. The optimum conditions were determined as follows: the initial sucrose concentration (X₁): 100 g/L; the initial peptone concentration (X₂): 11.31 g/L; the initial pH (X₃): 6.48; and the temperature (X₄): 24.2 °C. In the optimum conditions, the maximum exopolysaccharide (EPS) concentration (Y₁), the maximum pullulan concentration (Y₂), the specific growth rate (Y₃), the maximum specific pullulan formation rate (Y₄), and the pullulan yield (Y₅) were expected to be obtained as 37.078 and 35.372 g/L, 0.062 h⁻¹, 0.021 [g pullulan/(g mo.h)], and 53.681%, respectively. The observed values of Y₁, Y₂, Y₃, Y₄, and Y₅ were 36.950 g/L, 35.470 g/L, 0.064 h⁻¹, 0.036 [g pullulan/(g mo.sa)], and 54.480%, respectively, as a result of validation experiments. EPS samples were characterized by Fourier-transform infrared spectroscopy and scanning electron microscope analyses. The optimization process caused more than a 50% increase in EPS and pullulan concentrations. This study showed that the color-variant A. pullulans AZ-6 strain could become a significant industrial strain if it is explored further in the future to produce pullulan on a larger scale.