Production of extracellular polysaccharides, pullulan and β-glucan, was investigated with Aureobasidium pullulans. The optimized medium concentrations for the maximum production of polysaccharide was : $NaNO_3$ 5g/L, sucrose 50g/L and $K_2HPO_4$ 1g/L. The optimal pH for production of polysaccharide was 4 and over the optimum pH, the broth color changed from yellow to black and production of polysaccharide decreased. The optimal concentration of ascorbic acid not to produce melanin-like pigments was around 2-4g/L. The production of polysaccharide was affected by ascorbic acid in flask culture but not much in fermentor.
By batch fermentation without the control of pH, the optimal agitation speed for production of polysaccharide was 400rpm and the productivity of polysaccharide was 0.12g/L·hr. Under the control of pH at 4, optimal agitation speed for production of polysaccharide was 600rpm and the productivity of polysaccharide was 0.21g/L·hr.
By a fed-batch fermentation, 25.34g/L of polysaccharide was obtained by one time feeding and the productivity was 0.222g/L·hr. With a method of twice feeding 45g/L of polysaccharide was obtained and productivity was 0.345g/L·hr.
When the effect of pH was investigated in fermentor, the optimum pH for the production of polysaccharide was also 4.
For the assay of β-glucan and pullulan, the percentage of β-glucan in polysaccharide is about 65% without the control of pH. But under the control of pH at 4, the percentage of that is about 12%.
The scale-up study in 500L fermenter has shown the similar result to 5L fermenter.
