Optimization of pH for high molecular weight pullulan

Summary Pullulan is a polysaccharide produced by Aureobasidium pullulans. In this study, the effect of pH on the molecular weight of pullulan was investigated. High concentration of pullulan was obtained when initial pH was 6. Pullulan having molecular weight of 500,000–600,000 was produced at initial pH of 3.0, while pullulan with molecular weight of 200,000–300,000 was produced at pH above 4.5. To obtain high molecular weight pullulan with high concentration, pH was initially controlled at pH 6, followed by pH shift from pH 6 to pH 3. Transition of pH at 2 days of fermentation was observed to be optimum. Higher molecular weight pullulan was also obtained when sucrose concentration was 50 g/l compared to the result obtained at initial sucrose concentration of 20 g/l. Sucrose concentration and pH of the fermentation broth seem to be important parameters in obtaining high molecular weight of pullulan.