液相色谱-高分辨串联质谱法检测牛奶中A1和A2 β-酪蛋白

建立一种基于液相色谱\|高分辨串联质谱（LC-HRMS/MS）方法检测牛奶中A1和A2 β-酪蛋白. 采用等电点沉淀法从牛奶中提取酪蛋白, 经胰蛋白酶酶解后, 将酶解产物进行LC-HRMS/MS分析, 选择含有差异氨基酸残基（第67位）的肽段作为特征肽段对A1和A2 β-酪蛋白进行区分. 采用Tris-HCl缓冲溶液充分溶解酪蛋白, 在酶解反应体系中添加乙腈以提高酶解效率. 采用高分辨质谱和串联质谱技术, 进一步排除杂质产生的干扰信号. 采用该方法对市售4种普通牛奶和2种A2牛奶进行检测, 结果表明， 普通牛奶中A1 β-酪蛋白的含量约为A2 β-酪蛋白含量的2~4倍, 个别A2牛奶样品含微量A1 β-酪蛋白. 该方法可检测牛奶中的A1和A2 β-酪蛋白, 具有高可靠性、 高灵敏度等优点, 为A2奶源筛选和质量控制提供支持.

Determination of A1 and A2β-Casein in Milk by Liquid Chromatography-High Resolution Tandem Mass Spectrometry

We established a method based on liquid  chromatography-high resolution tandem mass spectrometry (LC-HRMS/MS) to detect A1 and A2 β-casein in milk. Caseins were extracted from milk by isoelectric point precipitation method,  after trypsin hydrolysis,  the hydrolysates were analyzed by LC-HRMS/MS method. The peptide containing varied amino acid moiety at the 67th position was selected as characteristic species to  distinguish A1 and A2 β-casein. Casein was fully dissolved in Tris-HCl buffer solution. The  acetonitrile was added to the enzymatic hydrolysis system to improve the enzymtic hydrolysis efficiency.  High resolution mass spectrometry and tandem mass spectrometry were used to eliminate the interference signal of impurity. Four kinds of common milk  and two kinds of  A2 milk  were tested by this method. The results show that the content of A1 β-casein is about 2—4 times that of  A2 β-casein in common milk,  while a small amount of  A2 milk samples contain trace A1 β-casein. This method can detect A1 and A2 β-casein in milk with advantages of high reliability and sensitivity,  which provides support for A2 milk source screening and quality control.