EMULSIFYING FUNCTION OF LACTOPHORIN AND CONDUCTION OF INHIBITION OF LIPOPROTEIN LIPASE

乳蛋白（Lactophorin，LP）是与牛乳脂肪球膜上可溶性糖蛋白的抗体反应而形成的一种主要糖蛋白，存在于乳清蛋白胨组分3中。LP富含疏水性氨基酸残基，并具有保护脂肪球聚结和凝集的糖链。本实验主要研究了LP的乳化能力和对脂蛋白脂酶的抑制作用。通过测量乳化活性、乳液稳定性、粘度、直径和乳液中小球的比表面积来评价乳化能力，所述乳液是通过在Polytron均质器（19，500 rpm）上在45 ℃下将1%蛋白质（包括LP）和25%乳脂的混合物在0.1M磷酸盐缓冲液（pH 7.0）中搅拌而制备的。1)LP在较短的乳化时间（30秒）和40 mg LP/g乳脂时形成的乳状液具有较高的乳化能力。2)增加LP浓度，乳化性能 关于我们 增加但是，乳液的粘度增加。3)LP在10 - 50%乳脂肪范围内以40 mg LP/g脂肪的水平形成水包油乳液。4)乳化能力受pH值的影响，乳化稳定性在pH值4时最低，在pH值7 ~ 10.5时最高。LP主要由28和18 KDa多肽组成。在pH 7下制备的乳液中的小球的表面上吸附的主要多肽为28 KDa，并且在pH 3、4和9.2下的乳液中均为28 KDa。脂蛋白脂酶（LPL）的抑制作用LPL在鲜牛乳中天然存在，但不作用于被脂肪球膜包裹的乳球中的乳脂。然而，部分破坏的脂肪球很容易被LPL水解。本研究利用超声乳中的固有LPL来检测LP对LPL的抑制作用。1)超声处理促进鲜牛乳中脂肪的分解。2)在蛋白酶-蛋白胨组分中，富含LP的组分-3对LPL有抑制作用，40 mg LP/ml超声乳中的LP抑制了约30%的脂肪酸释放。3)LP通过组分-3级分的凝胶过滤纯化。超声波处理乳对LPL的抑制作用随纯化LP浓度的增加而增强。在37 ℃下，40 mg/ml的LP在60 min内抑制了LPL释放脂肪酸的80%。少

Lactophorin (LP) reacts with the antibody of soluble glycoprotein from bovine milk fat globule membrane and present as the major glycoprotein in the component-3 of proteose peptone fraction of milk whey. LP is rich in hydrophobic amino acid residues and possesses saccharide chain which protect coalescence and agglutination of fat globules. In the present study, it has been undertaken to study the emulsifying ability of LP and inhibition of lipoprotein lipase by LP.1. Emulsifying function Emulsifying ability was evaluated by measuring emulsifying activity, emulsion stability, viscosity, diameter, and specific surface area of globules in emulsion which was prepared by homogenizing a mixture of 1% protein including LP and 25% milk fat in 0.1 M phosphate buffer (pH 7.0) on a Polytron homogenizer (19,500 rpm) at 45ﾟC. 1) LP formed emulsion with higher emulsifying ability at short emulsifying time (30 sec)and 40 mg LP per g of milk fat. 2) Increasing LP concentration, emulsifying properties … More increased. However, viscosity of emulsion increased. 3) LP formed oil in water emulsion in the range of 10 and 50% milk fat in the level of 40 mg of LP per g fat. 4) Emulsifying ability was influenced by pH; emulsion stability was lowest at pH 4, which in isoelectric point of LP, but high at pH 7-10.5) LP consists of mostly 28 and 18 KDa polypeptides. Major polypeptide adsorbed on the surface of globules in emulsion prepared at pH 7 was 28 KDa and both in emulsion at pH 3, 4, and 9.2. Inhibition of lipoprotein lipase (LPL) LPL is contained indigenously in fresh bovine milk, but not act on milk fat in the globule which is enveloped with fat globule membrane. However, partially destructed fat globules are easily hydrolyzed by LPL. In this study. indigenous LPL in sonicated milk was utilized for examining the inhibitory action of LP to LPL. 1) Lipolysis in fresh bovine milk was accelerated by sonic treatment. 2) Of proteose-peptone fractions, component-3 fraction enriched in LP showed the inhibitory effect on LPL;LP in 40 mg LP per ml of sonicated milk inhibited about 30% of the release of fatty acid. 3) LP was purified by gel filtration of component-3 fraction. Inhibition to LPL in sonicated milk increased with the increase of purified LP concentration. LP in 40 mg/ml of sonicated milk inhibited about 80% of the release of fatty acid by LPL for 60 min. at 37ﾟC. Less