Selectivity Aspects of Lipolysis of Milkfat (Butteroil) by Immobilized Pregastric Esterases from Kid Goats and Lambs

Pregastric esterases derived from the salivary tissues of kid goats and lambs were immobilized by physical adsorption in a continuous flow, hollow‐fiber reactor and subsequently used to hydrolyze anhydrous milkfat, thereby producing lipolyzed butteroils. These 2 esterases were used in separate trials conducted at temperatures of 40 °C, 45 °C, and 50 °C and pH values of 5.0, 6.0, and 7.0. High‐performance liquid chromatography (HPLC) was used to determine the relative proportions of the different fatty acid residues released as functions of the reactor space time for the indicated operating conditions. For both esterases, the rates of the lipolysis reactions were fastest at 40 °C and a pH of 6.0. The rates of release of the native individual fatty acid residues were modeled using expressions of the generalized Michaelis‐Menten form based on a ping pong bi bi mechanism. Nonlinear regression analyses indicated that for both esterases, the experimental data were consistent with the form of the ping pong bi bi mechanism for which the rate controlling step is deacylation of the enzyme.     

Lipolysis of Butter Oil by an Immobilized Kid Goat Pregastric Esterase

ABSTRACT: A kid goat pregastric esterase immobilized in a continuous flow, hollow-fiber reactor was employed to hydrolyze anhydrous milkfat, producing lipolyzed butter oil. The effects of temperature and pH on the rate of lipolysis were monitored by titration of the effluent stream for total acidity. The overall rate of hydrolysis was fastest at 40 °C and pH 6.0. The reaction rate was modeled by an expression of the general Michaelis-Menten form based on a ping pong bi bi mechanism. Nonlinear regression analyses indicated that the experimental data were consistent with the form of the ping pong bi bi mechanism that assumes that the rate-controlling step is acylation of the enzyme.     

PERMEATE FLUX BEHAVIORS UNDER VARIOUS PRESSURE DECLINES IN MEMBRANE ULTRAFILTRATION MODULE

The effects of operating conditions on the permeate flux for ultrafiltration of aqueous solution of PVP-360 in hollow-fiber membrane modules, have been investigated based on the exponential model with the consideration of the declines of transmembrane pressure along the axial direction in the hollow fibers. It is seen that the exponential model qualitatively correlates the experiment. The correlation prediction may be improved if the exact but complicated pressure distribution is used for the derivation of presented model.     

Esterification of lauric acid using lipase immobilized in the micropores of a hollow-fiber membrane

A porous anion-exchange hollow-fiber membrane was prepared by radiation-induced graft polymerization and chemical modification to immobilize lipase for enzymatic reaction in an organic solvent. The amount of anion-exchange group introduced to the porous hollow-fiber membrane was 2.5 mol/kg_fiber. A lipase solution was allowed to permeate through the porous anion-exchange hollow-fiber membrane, and lipase molecules that adsorbed onto the grafted polymer brush were cross-linked with glutaraldehyde. The lipase was immobilized at a density of 0.14 kg_lipase/kg_fiber, which was equivalent to a degree of multilayer binding of 20. Esterification was carried out by passing a solution of lauric acid and benzyl alcohol in anhydrous issoctane through the lipase-immobilized membrane, and lipase activity was determined. A reaction percentage of 50% was achieved at space velocity 68 h⁻¹. The maximum immobilized lipase and native lipase activities were 8.9 and 0.38 mol/(h·kg_lipase), respectively. Thus, the activity of the immobilized lipase was 23.4 times higher than that of the native lipase.     

The effect of heat-treatment on the ultrafiltration performance of polyethersulfone (PES) hollow-fiber membranes

Polyethersulfone (PES) hollow-fiber membranes were prepared by the dry-wet spinning method and then heated in an oven at different temperatures to investigate the effect of heat-treatment on their ultrafiltration performance. It was found that the hollow-fiber membranes shrank by heat treatment, as evidenced by a decrease in flux and an increase in solute separation, although there was no visible change in the hollow-fiber dimension. The best results were obtained when the hollow fibers were heated at 150°C. A further investigation was made on the effect of the heating period, while the temperature was fixed to 150°C. It was found that the best combination of the temperature and the heating period was 150°C and 5 min.     

聚砜中空纤维膜在丙烯酰胺微生物转化中的应用基础研究

将聚砜为材料的中空纤维膜组件应用于丙烯腈水合转化为丙烯酰胺的微生物转化和膜分离耦合过程,对其特性进行了初步研究.结果表明:该膜对此反应体系有很好的适用性,通过中空纤维膜使反应液和菌体得到有效的分离,实现了膜分离耦合的酶催化反应过程.20℃时,在不更新菌液的情况下,持续操作5h,丙烯腈转化率达到99%,发酵菌液可催化合成丙烯酰胺2.722g/(mL·h),产物中没有检测到副产物丙烯酸.膜材料的应用研究为长期连续化生产过程的研究打下了基础.该工艺过程以自由细胞替代固定化细胞,实现了连续化操作,具有良好的工业应用前景.     

基膜表面处理对反渗透复合膜性能的影响

采用表面活性剂十二烷基磺酸钠(SDS)和弱极性试剂异丙醇(IPA)作为聚砜基膜表面改性试剂,观察其对中空纤维反渗透复合膜性能的影响.结果表明:选择不同处理剂在一定浓度和时间下处理基膜,所制备复合膜的膜通量提高明显,截留率基本不变;若处理时间过长或者处理剂浓度过大,则膜通量下降.     

轴向扩散对中空纤维膜萃取器传质性能的影响

通过测量聚丙烯中空纤维膜萃取器壳程和管程流动的RTD曲线 ,证实了中空纤维膜器管程与壳程流动均较为复杂 ,与理想平推流和理想全混釜相差较大。膜器管程流动的轴向返混程度随着流速增加而减小 ,而膜器壳程流动的轴向返混程度随着流速的增加而增大。将两相流轴向扩散模型用于描述传质情况 ,比较了表观传质系数和真实传质系数 ,计算了中空纤维膜萃取器中真实的浓度剖面。结果表明 ,中空纤维膜萃取器轴向扩散导致表观传质系数比真实传质系数下降 30 %左右 ,所以在进行膜器设计和放大时 ,中空纤维膜器的轴向扩散不可忽略。     

中空纤维膜低压超滤处理含油废水的数学模拟

提出一个不可忽略轴向压力降和膜渗透速率轴向变化的中空纤维膜低压超滤处理含油废水的传质模型 ,采用正交配点法并结合MATLAB软件进行模拟 ,解出速度分布和浓度分布 ,得到超滤速率的变化规律 ,与实验数据吻合很好 .用模拟结果讨论Peclet数对超滤的影响 ,并分析中空纤维丝内径向速度分布 ,为超滤膜及工艺条件的选择提供了重要依据 .     

mufiltration of polydispersed suspension by a membrane screen/hollow-fiber composite module

Membrane and hollow-fiber technologies have widely been used in pure water production, and are increasingly used in conventional water and wastewater treatment for solid—liquid separation. A major challenge to these applications is to prevent or reduce particle fouling so that the membrane or hollow-fiber modules can be operated at a higher permeation flux and over a longer period of time. In this study, a membrane screen/hollow-fiber composite module has been developed for the mufiltration of polydispersed suspensions. The module combines a cylindrical membrane of larger pores as a screen and a bundle of hollow fibers of smaller pores for polishing treatment. Both cross-flow and dead-end filtrations occur in the same module. Experiments were conducted at various concentrations with kaolin particles of size ranging from 0.5 μm to 10 μm. The results showed that the membrane screen effectively removed larger particles from the permeating flow and reduced solid loading to the hollow fibers. As a result, the composite module generated considerably higher permeation flux, as compared to a similar hollow-fiber module without the membrane screen. It was found that larger particle deposition was more significantly affected by the cross flow, and initially deposited particles contributed greater specific resistance to the permeating flow.