生鲜乳及工业奶粉中酸溶性非蛋白氮质量分数的测定

Determination of Acid-Soluble Non-Protein Nitrogen in raw milk and milk powder

以生鲜乳或工业奶粉为原料采用不同的沉淀方法沉淀蛋白质,并采用凯氏定氮法测定上清液中的蛋白质增加量,即为酸溶性非蛋白氮的添加量。通过对几种沉淀方法进行对比,选择三氯乙酸法,并通过添加未水解蛋白、部分水解蛋白、完全水解蛋白、尿素和甘氨酸等物质,测定该方法的回收率。结果表明:用质量浓度150 g/L的三氯乙酸沉淀蛋白质,效果较好,回收率在81.2%～101.8%之间。

Raw milk or industrial milk powder was precipitated by different methods. The content of protein increased in the supematant was measured by Kjeldahl nitrogen method, which was the content of acid soluble non-protein nitrogen added. After comparing different methods of precipitation, trichloroacetic acid precipitation method as the best one was used in this paper. By adding non-hydrolyzed protein, partially hydrolyzed protein, complete hydrolysis of protein, urea, glycine and other substances, the recovery of this method was determined. The results showed that 150 g/L trichloroacetic acid was enough to precipitate the proteins with the recovery in the range between 81.2%-101.8%.