Optimization of High Molecular Weight Pullulan Production by Aureobasidium pullulans in Batch Fermentations

Of five strains of Aureobasidium pullulans studied, NRRL Y-2311-1 yielded the highest titer (26.2 g/L) of pullulan and formed the lowest amount of melanin-like pigment. Sucrose was superior to glucose as the carbon and energy source on the basis of yield and titer of pullulan produced. Pullulan titer was higher (26.2 vs 5.1 g/L), biomass concentration was lower (6.9 vs 12.7 g/L), and DO was lower (0 vs 60% of saturation) when the fermenter was agitated by a marine propeller compared to Rushton impellers. Pullulan produced by strain NRRL Y-2311-1 ranged in weight-average molar mass (Mw) from 486 KDa and number-average molar mass (Mn) from 220 Da on day I of growth to 390 KDa and 690 Da on day 6; M(W) declined by about 35% from day I to day 3, the day of maximum pullulan titer. For the other strains, the ranges of molar mass on the day of maximum pullulan titer were 338-614 KDa (M(W)) and 100-6820 Da (Mn).