Kinetic enhancement of starch bioconversion in thermoseparating aqueous two-phase reactor systems

The extractive bioconversion of starch in an aqueous two-phase reactor system (ATPRS) was studied through experimentation and mathematical modeling. The phase-forming components included PEO-PPO-2500 (a random copolymer of ethylene oxide and propylene oxide with molecular weight of 2500) and MgSO₄. Partitioning of glucose and maltose in the PEO-PPO/MgSO₄ system was determined. Hydrolysis rates of soluble and corn starches in one-phase and aqueous two-phase reactor systems were compared. Starch consumption and glucose production kinetics were evaluated for α-amylase and amyloglucosidase separately as well as synergistically. A Michaelis-Menten kinetic model with product inhibition was employed to describe enzymatic hydrolysis. This model was expanded to include reaction with simultaneous partitioning for the two-phase system. Parametric studies of starch hydrolysis in the ATPRS with respect to the partition coefficient of the final hydrolysis product, glucose, were performed to simulate starch conversion profiles. The use of the ATPRS reduced the hydrolysis time to almost half of that for single-phase processing. These results were confirmed experimentally. The PEO-PPO-2500/MgSO₄ system enhanced the starch hydrolysis by decreasing the glucose inhibition. The hydrolysis reaction was completed in 10 h in ATPRS system while taking 18 h in one-phase aqueous system. The goodness of fit between model and experiments demonstrates that thermodynamic partition data, coupled with the lumped kinetic model for dual enzymatic hydrolysis and product inhibition are appropriate for describing the two-phase bioreactor system.