人为添加三聚氰胺液态乳中蛋白质含量测定方法的研究

Research on the methods of protein determination after added melamine in milk

用GB/T5413.1《婴幼儿配方食品和乳粉蛋白质的测定》、GB/T 21704—2008《乳与乳制品中非蛋白氮含量的测定》和ISO8968-5:2001/IDF 20-5:2001《Milk-Determination of nitrogen content-Part 4:Determination ofprotein nitrogen content》3种国内外现行标准方法,对液态乳中添加三聚氰胺后的蛋白质、非蛋白氮和蛋白氮含量进行了测定,并与双缩脲比色法和三氯乙酸-双缩脲比色法测定的蛋白质含量进行了比较。结果表明:利用前3种标准方法分别测定液态乳添加三聚氰胺后的蛋白质、非蛋白氮和蛋白氮含量,误差率依次为46.60%、93.00%和52.70%;利用双缩脲比色法和三氯乙酸-双缩脲比色法测定液态乳添加三聚氰胺后的真蛋白含量,误差率分别为2.87%和2.22%,比上述3种标准方法更为准确,说明它们既可以排除添加尿素、甘氨酸等非蛋白氮的干扰,又可以准确测定液态乳中的蛋白质含量;其中三氯乙酸-双缩脲比色法比双缩脲比色法的适用性更广。

The contents of protein, non-protein nitrogen and pro!ein nitrogen were determined using GB/T5413.1 ,GB/T 21704-2008 and ISO 8968-5：2001/ IDF 20-5：2001 methods after adding melamine in milk, and the results were compared with the standard methods, the Biuret Spectrophotometry methord （B method） and Trichloroacetic acid and Biuret Spectrophotometry method （T ＋ B method）. It is shown from the results that the error rates were 46.60%, 93.00% and 52.70% respectively for the methods of GB/T5413, GB/T 21704 - 2008 and ISQ 8968-5：2001 to determine the content of protein, non-protein nitrogen and protein nitrogen in melamine added milk, while the error rates of B method and T＋ B method were 3.00% and 3.05% respectively. The B method and T＋ B method could determine the content of protein after adding Urea and Glycin. Compared with the B method, the T ＋ B method can determined the content of protein accuratelyafter adding hydrolysatum in milk.