Standardization of major constituents of bovine milk fat globule membrane

1.以牛乳为原料制备乳脂球膜(MFGM)，1)洗涤奶油搅拌，回收酪乳，2)膜材料经超滤浓缩，高温-短时巴氏杀菌，3)冷冻干燥。2)分别用高效液相色谱法和十二烷基硫酸钠-聚丙烯酰胺凝胶电泳法测定乳脂球膜的磷脂组成和蛋白质组成。磷脂主要由磷脂酰胆碱、磷脂酰乙醇胺和鞘磷脂组成。蛋白质由PAS-1、-4、-5、-6、-7和CB-1组成。为了保证MFGM制剂的质量，对MFGM进行了高温-短时巴氏杀菌。测定了高温-短时巴氏杀菌稳定的FAD-焦磷酸酶和高温-短时巴氏杀菌变性的碱性磷酸酶的活性，以检验巴氏杀菌的程度。MFGM制剂中的碱性磷酸酶失活，而FAD-焦磷酸酶活性大部分保持不变，表明这些标志物是有用的。4.评价MFGM制剂的乳化能力。将1%MFGM和25%乳脂在pH7.0的磷酸盐缓冲液中，在Polytron匀浆机(19000rpm)上匀浆2min，制得乳状液。结果表明，MFGM制备的乳状液具有较高的乳化活性和乳化稳定性，脂肪球的中位数直径约为3-5 mm。建议从MFGM的磷脂、膜蛋白等成分的组成、避免变性的高温短时间巴氏杀菌和MFGM的乳化功能三个方面对MFGM的制备进行评价。

1.Milk fat globule membrane (MFGM) was prepared from bovine milk in the following procedure, 1) washed cream was churned and buttermilk was recovered, 2) membrane materials were concentrated by ultrafiltration through membrane and pasteurized by high temperature-short time method, 3) finally MFGM was freeze-dried.2.Phospholipid and protein composition as a representative component of MFGM were measured by HPLC and SDS-PAGE,respectively. Phospholipid was composed of mainly phosphatidyl choline, phosphatidyl ethanolamine, and sphingomylin. Protein consisted of PAS-1, -4, -5, -6 and -7 and CB-1. These components were found in every MFGM preparations.3.For keeping the quality of MFGM preparation, MFGM was pasteurized by high temperature-short time method. For examinating the degree of pasteurization, the activity of FAD-pyrophosphatase which is stable for high temperature-short time pasteurization and of alkaline phosphatase which is denatured by high temperature-short time pasteurization were assayd. Alkaline phosphatase in the MFGM preparation was inactivated, whereas most of FAD-pyrophosphatase activity was kept, suggesting these markers are useful.4.Emulsifying ability of MFGM preparation was evaluated. Emulsion was prepared by homogenizing (2min) on Polytron homogenizer (19,000rpm) a mixture of 1% MFGM and 25% milk fat in phosphate buffer (pH7.0). It was found that emulsion made by MFGM preparation had a higher emulsifying activity and emulsion stability and the median diameter of fat globule was about 3-5 mum.5.It was recommended that MFGM preparation might be evaluated from three points of composition of MFGM constituents such as phospholipid and membrane protein, pasteurization by high temperature-short time method in order to avoid the denaturation, and function of MFGM such as emusification.