牛羊乳酪蛋白制备及电泳分析比较

采采用新鲜和复原的牛羊乳为原料，等电点沉淀，通过洗涤、干燥等步骤分别制得牛乳和羊乳酪蛋白，用凯氏定氮法对其进行定量检测，应用十二烷基硫酸钠聚丙烯酰胺凝胶电泳（SDS—PAGE）分析比较牛羊乳酪蛋白组分差异。结果表明：牛乳酪蛋白得率为86．75％，羊乳酪蛋白得率为90．55％，高含量的酪蛋白主要集中在电泳图谱的中分子量组，可分为ds，CN、as2-CN、β-CN和K—CN，牛羊乳as2-CN分子量羊乳大于牛乳，牛乳a-CN含量比较多，羊乳β—CN含量比较多，鲜乳与复原乳全蛋白主要组分在电泳图谱中除酪蛋白差别外，上端的高分子量组清蛋白区羊乳IgG重链的分子量比牛乳小。应用蛋白质电泳分析技术可以区分羊乳和牛乳的蛋白质组分，等电点沉淀法制备酪蛋白的方法简单，易于操作。

Preparation and electrophoretie analysis of casein in cow and goat milk

Using fresh and recovery cow and goat milk as raw material, cow and goat casein was obtained by isoelectric point precipitation, steps of washing and drying, respectively. Quantitative detection was taken by Kjeldahl method and differences of composition of cow and goat casein protein were analysed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis （SDS-PAGE）. The results showed that： casein yields were 86.75% and 90.55%, respectively for cow and goat milk. And the high content composition is concentrated in in the middle of the molecular weight of electrophoretic patterns, which can be divided into etsrCN, as2-CN, β-CN and K-CN. as2-CN molecular weight of goat milk was higher than that of cow milk. content of a-CN of cow milk was more than that of goat milk, while goat milk contained more β-CN than that of cow milk. Except for casein, the high molecular weight albumin area at the top of electrophoresis was also differed by the whole milk protein of fresh and recovery milk, molecu- lar weight oflgG heavy chain of goat milk was higher than that of cow milk. The protein electrophoresis analysis technology can distinguish compo- sition of goat and cow milk protein, and preparation of casein by isoelectric point precipitation is simple and easy.