Simultaneously enhanced production and molecular weight of pullulan using a two-stage agitation speed control strategy

BACKGROUND: Pullulan with high molecular weight (Mw) is attractive for industrial application. Previous studies indicated that high yield and high Mw of pullulan cannot be simultaneously obtained under constant agitation speeds or constant dissolved oxygen levels during batch pullulan fermentation. In this study, a two-stage agitation speed control strategy was developed to obtain pullulan with both high yield and high Mw. RESULTS: Batch pullulan production at various constant agitation speeds ranging from 200 to 600rpm was carried out in a 5L stirred tank fermentor. Based on kinetic analysis of batch processes, activity assays of the enzymes associated with pullulan biosynthesis and biodegradation, and intracellular energy supply under different constant agitation speeds, a two-stage control strategy that shifted the agitation speed from 500 to 400rpm at 18h proved to effectively achieve simultaneous high yield of high Mw pullulan. CONCLUSION: A maximum pullulan concentration of 27.4gL^-1 and final Mw of 3.09×10⁶Da were obtained using the two-stage agitation speed control strategy, which were both greatly improved compared with those obtained at constant agitation speeds.