The Kinetic Model Of Casein Hydrolysis By Pancreatin And The Studies For Improving The Performance Of Enzymatic Membrane Reactor By Backflushing And Surface Modification

The kinetics for casein hydrolysis by pancreatin in batch and continuous equipments were studied, and the backflushing technology and surface modification were applied in enzymatic membrane reactor (EMR) for improving the separation efficiency by decreasing the effect of concentration polarization and protein absorption respectively. The detailed results are as follows: The inactivity and operation stability of pancreatin: The apparent kinetic constants of heat inactivation and autolysis for pancreatin at different temperature were obtained by measuring the inactive velocity at different pancreatin concentrations. When pancreatin was not protected by substrate, serious loss of its activity caused by heat inactivation and autolysis was observed in batch and continuous equipments. But if protected by casein, no obvious loss of its activity was observed.Kinetic studies for batch hydrolysis of casein by pancreatin: Substrate and product inhibition were testified, and the kinetic constants of Km, K+2, Ks and KP were obtained with the values of 0.227g l-1, 0.127min-1, 64.1 g l-1, and 72.6g l-1 respectively. As a result, a kinetic model was built. According to this model, the hydrolysis process was modeled, and the initial substrate concentration was optimized. Also, it was approved that casein could protect pancreatin from inactivation to a high degree based on the kinetic studies.A kinetic model for continuous enzymatic hydrolysis of casein: By making some suitable hypothesis, a kinetic model for the hydrolysis process was built. The kinetic constants, Km of 19.7g l-1 and Vmax of 0.284min-1, were obtained. By analysing the kinetic model, it can be concluded that a high hydrolysis efficiency can be achieved when operated at high initial substrate concentration and high permeation flux. This was approved in the experiments with constant ultrafiltration pressure.The application of backflushing technology: An easily-realized backflushing technology was applied in the continuous hydrolysis of casein for decreasing the effect of concentration polarization. Water was selected as the right backflushing material. The backflushing pressure, interval and duration were optimized as 0.1 MPa, 10 min and 10 s respectively, and the backflushing pressure was considered as the most important factor of affecting backflushing efficiency.The application of neural network in modeling backflushing: The system of reaction-separation-backflushing was determined as a nonlinear one. The neural network approach was found to be capable of modeling this complex process accurately. With a three-layered network model, the effect of duration and interval on backflushing efficiency was modeled, and duration was approved as a more important factor of affecting backflushing efficiency. Also, backflushing conditions were optimized based on this model. In succession, the variations of Je and Jb with time under the optimized conditions were modeled by using simple networks.Hydrophilic modification of polysulfone membrane: The modification conditions were optimized as: the ratio of acrylic acid to phosphoric acid, 3:1 (v/v); the ratio of acrylic acid to stannic chloride, 1:0.05(mol/mol); reaction time, 60 min and 30oC. The grafting of carboxyl group to the membrane surface was proved by infrared spectroscopy, and no degradation of the membrane skin and framework but with fewer pores than before were validated by scanning electronic microscopy. The experiments of separating BSA solution indicated that the function of resisting protein absorption for modified membrane was much better than that for unmodified membrane. In the process of separating casein hydrolysate, the permeate molecular weights and permeation flux of modified membrane were little lower than those of unmodified membrane.