牛奶中酪蛋白结果分析

The analysis results of casein in milk

目的通过对市售牛奶采用索氏(Soxhlet)法和等电点法分别测定牛奶中酪蛋白的结果和对比分析,揭示这两种测试方法的优缺点。方法采用索氏(Soxhlet)法抽提粗脂肪,即利用低沸点的有机溶剂(乙醚或石油醚)回流抽提,除去有机溶剂,以增加油的重量来计算粗脂肪的含量。利用在PI时溶解度最低的原则,将酪蛋白沉淀,用乙醇洗涤沉淀物,除去脂类杂质后得到纯的酪蛋白,并利用紫外吸收光谱法来测定蛋白质的含量。结果两种方法测定牛奶样品中酪蛋白含量分别为等电点法2.33g/100mL,索氏抽提法0.730g/100 mL,均低于牛奶包装袋上所标注的牛奶中的3.5 g/100 mL.结论所测市售蒙牛袋装牛奶的营养成分基本符合标准。奶中酪蛋白测定索氏法测定结果排除了脂肪干扰,其值略低,但更合理。

Objective To reveal the advantages and disadvantages of the two test methods through the results of casein in milk by the methods of Soxhlet（Soxhlet） and isoelectric point.Methods We used Soxhlet（Soxhlet） extracted crude method,namely the use of low-boiling point organic solvent（ethanol or petroleum ether） back extraction to remove organic solvents,in order to increase the weight of the oil to calculate the fat content.The lowest solubility in the PI when using the principles of the casein precipitation,ethanol washing sediment,obtained after removal of impurities in pure lipid casein.UV absorption spectrometry was used to determine protein content.Results The content of casein in milk samples were2.33g/100ml by method of isoelectric point and 0.730g/100 mL with Soxhlet extraction method.The result were lower than those marked on the bags of milk in milk of 3.5mg / 100 mL.Conclusion The nutritional content of milk of Mengniu bags meet a criterion.Determination of milk casein Soxhlet fat determination results exclude interference,and its value is slightly lower but more reasonable.