Determination of A2 -casein and total -casein in liquid milk and milk powder by capillary zone electrophoresis

beta-casein (beta-CN) is one of the major casein proteins in cow milk. There are 13 different variants documented for beta-CN in cow milk, among which A1 and A2 are the major variants. The separation and quantitation of A2 beta-CN are imperative for A2 dairy products. A new capillary zone electrophoresis (CZE) method with UV detection at 214 nm was established for the separation and quantification of the A2 variant and total beta-CN content in cow milk and milk powders. The separation of beta-CN variants was achieved on bare fused silica capillaries (50 mu m x 30/40 cm (effective/total length))). The separation buffer was a mixture of 4 mol/L urea, 0.2% (mass fraction) hydroxypropyl methylcellulose, 140 mmol/L citric acid, and 50 mmol/L disodium hydrogen phosphate buffer (pH 2.7). The corrected peak areas and the concentrations of total beta-CN and the A2 variant showed good linearity, with correlation coefficients (r(2)) ranging from 0.9968 to 0.9997. The intra-day precisions for A2 beta-CN and total beta-CN determination in four samples (two pasteurized milk samples and two milk powder samples) were in the ranges of 2.4%-4.7% and 2.6%-4.8%, respectively. The inter-day precisions for A2 beta-CN and total beta-CN determination in four samples were in the ranges of 4.0%-6.3% and 3.9%-6.7% respectively. The recoveries of A2 and total beta-CN ranged from 85.5% to 106.4%. With the established CZE method, the A2 beta-CN variant and total beta-CN protein in liquid and powder bovine milk products could be separated and accurately quantified. By calculating the A2 beta-CN content in the total beta-CN, the quality of A2 dairy products can be evaluated, and this in turn would aid in the protection of consumer rights.