Determination of the total concentration of casein and β-lactoglobulin by indirect competitive ELISA in milk and dairy products

The main purpose of this work was to develop an assay as a means of quality control in milk and dairy products. As specific and high abundant proteins in milk and diary products, casein and b-lactoglobulin were chosen as the targets, and an indirect competitive enzyme-linked immunosorbent assay(ELISA) was developed for determination of the total concentration of casein and b-lactoglobulin. The detection limit of the assay was 79.07 ng/mL,and a working range of the calibration curve was from140.6 to 36,000 ng/mL. The intra-assay and inter-assay coefficients of variations were 4.7 % and 6.5 %, respectively. The recoveries ranged from 94.1 % to 106.6 %. The developed ELISA assay was used to detect the total concentration of casein and b-lactoglobulin in liquid milk and milk powder. The results indicated that the developed assay was very specific, and the addition of nonprotein nitrogen(such as melamine, cyanuric acid, and urea) and vegetable protein did not affect the detection. The good performance of the assay makes it suitable for use in the quality control of milk and dairy products.