【作者】 董春华；

【导师】 何志敏；

【作者基本信息】 天津大学 ， 化学工程， 2004， 博士

【摘要】 本文对酪蛋白-胰酶体系间歇和连续水解动力学进行了研究;并分别针对连续酶解过程中浓差极化和蛋白吸附两类主要膜污染现象,考察和优化了反冲技术和表面改性两种方法对膜性能的改善。具体研究内容如下:胰酶失活及其操作稳定性:通过检测不同浓度胰酶失活速率,获得了不同温度下胰酶热失活及自水解表观速率常数;无底物保护时,热失活和自水解将导致间歇操作和连续操作酶失活严重;但在底物酪蛋白的保护下,两种操作中胰酶在5个小时内都表现出较高活性,残余酶活始终接近初始酶活。酪蛋白的胰酶间歇水解动力学研究:研究证明胰酶间歇水解酪蛋白过程存在底物抑制和产物抑制现象,获得动力学常数Km=0.227g l-1,K+2=0.127min-1, Ks=64.1 g l-1和KP= 72.6g l-1,并建立间歇水解动力学方程;依此方程对水解过程进行模拟和优化,实验值和模拟值吻合较好,并得到最优初始底物浓度随水解度变化方程;根据此动力学研究,证明底物酪蛋白对胰酶存在着极强保护作用。酪蛋白连续酶解过程动力学模型:在对酶解机制作出合理假设的前提下,建立了酪蛋白连续酶解过程动力学模型,获得动力学常数Km=19.7g l-1、Vmax=0.284min-1;理论分析该模型可得:高初始底物浓度、高渗透通量是获得高水解效率(S0*J*X)的条件,该结果在恒压操作实验中得到验证。反冲技术的应用:设计了一套简单且易于操作的反冲装置应用于胰酶连续水解酪蛋白过程以降低浓差极化的影响;水被选择为合适的反冲介质;反冲操作条件优化为:反冲压力0.1MPa,反冲时间10s,反冲间隔时间10min;其中反冲压力是影响反冲效率的最主要因素。神经网络在反冲技术模拟中的应用:确定BP神经网络为模拟集反应-分离-反冲于一体的非线性系统的强有力工具;采用一个三层BP网络模型,模拟了反冲时间和反冲间隔时间对反冲效果的影响,并证明反冲时间对反冲效果的影响程度高于反冲间隔时间;利用已训练网络,优化选择了反冲时间和反冲间隔时间;采用简单网络分别对最优反冲条件下的Je和Jb随时间变化趋势进行了模拟。亲水化改性聚砜超滤膜:确定了最优改性条件为:丙烯酸与磷酸体积比3:1,丙烯酸与四氯化锡摩尔比1:0.05,30oC,反应60min;对改性膜的红外检测表明羧基已被接枝到膜表面;扫描电镜分析证明膜骨架和膜面都未受到损坏,但膜孔有所减少;通过超滤不同浓度的BSA溶液,表明改性膜比未改性膜具有良好的抗蛋白吸附性能;应用改性膜分离酪蛋白酶解液过程中,其截留分子量和渗透通量都比未改性膜的略有降低。更多还原

【Abstract】 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.更多还原