酪蛋白沉淀检测方法及其在牛乳经济掺假鉴定中的应用

Precipitation determination of casein and its application for economic adulteration identification in milk

试验表明酪蛋白等电点沉淀检验方法的最适检测条件为:10%乙酸溶液,磁力搅拌,pH4.4～4.8,3000 r/min离心15 min,102℃直接干燥法。通过检测,生牛乳、银桥纯牛奶、市售便宜奶粉、乳清粉、食用明胶、三聚氰胺、大豆分离蛋白粉的酪蛋白质量分数(g/g蛋白质)分别为79.8%、78.7%、0、0、0、0和90.3%。结果表明,本检测方法能够很好的检测正常牛乳的酪蛋白含量,并能对市售便宜奶粉、乳清粉、食用明胶和三聚氰胺进行经济掺假鉴定,结合对产品豆腥味的感官评价和对假酪蛋白色泽偏暗的颜色测定的方法,可以对大豆分离蛋白粉进行掺假鉴定,验证了纯牛乳制品掺假检验的定量指标:酪蛋白质量分数(g/g蛋白质)≥73%。

The optimal testing conditions of casein isoelectric precipitation determination method were 10% acetic acid solution, magnetic Stir, pH 4.4-4.8, centrifugating at 3000 r/min for 15 min, direct drying at 102 ℃. The percentages of casein content （g/g protein） of raw milk, Yinqiao pure milk, marketing cheap milk powder, food gelatin, melamine, soy protein isolate powder were 79.8%, 78.7%, 0, 0, 0, 0 and 90.3% respectively. The results showed that this determination method could well test the casein content in normal milk and could identify the economic adulteration of marketing cheap milk powder, food gelatin, melamine and could also identify the adulteration of soy protein isolate powder combining sensory evaluation of beany flavor and darksome color testing of fake casein. The testing data validated that the quantitative index for adulteration testing in pure milk products was the percentage of casein content（g/g protein）not less than 73%.