EMULSIFYING FUNCTION OF LACTOPHORIN AND CONDUCTION OF INHIBITION OF LIPOPROTEIN LIPASE

催乳素(Lactophorin，LP)与牛乳脂肪球膜中的可溶性糖蛋白抗体发生反应，是乳清蛋白调组分-3中的主要糖蛋白。LP富含疏水氨基酸残基，并具有保护脂肪小球聚集和凝集的糖链。本研究对脂蛋白的乳化能力及其对脂蛋白脂肪酶的抑制作用进行了研究。通过测定乳化液中乳球的乳化活性、乳化稳定性、粘度、直径和比表面积来评价乳化液的乳化性能。乳化液中含有1%蛋白质和25%乳脂，在0.1M磷酸盐缓冲液(pH 7.0)中均质，在45ﾟ的温度下，均质机(19,500转/分)进行均质。1)乳化液在较短的乳化时间(30秒)和40 mg/g乳脂条件下形成乳化能力较强的乳状液。2)增加LP浓度，乳化性能…增加了更多。但是，乳液的粘度有所增加。3)乳脂含量为10%~50%，乳脂含量为40 mg/g脂肪时，乳清形成水包油乳状液。4)乳化力受pH的影响，乳状液稳定性在pH为4时最低，在等电点，但在pH为7~10.时较高。5)乳状液主要由28和18 KDa多肽组成。在pH为7的乳状液中，吸附在微球表面的主要多肽为28 KDa，在pH为3、4和9.2的乳状液中，两者都是吸附在微球表面的多肽。脂蛋白脂酶(LPL)抑制作用存在于新鲜牛乳中，但不作用于被脂肪球膜包裹的乳球中的乳脂。然而，部分破坏的脂肪小球很容易被LPL水解。在这项研究中。利用超声乳中的国产LPL考察了LP对LPL的抑制作用。1)超声处理加速了新鲜牛乳中的脂肪分解。2)在蛋白质-蛋白内酯组分中，富含Lp的组分3对LPL有抑制作用，每毫升Lp中Lp含量为40 mg时，可抑制约30%的脂肪酸释放。3)组分-3的凝胶过滤纯化Lp。随着纯脂浓度的增加，超声乳对LPL的抑制作用增强。40 mg/mlLP能抑制LPL释放约80%的脂肪酸，作用60min。在37ﾟC以下

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