MEASUREMENT OF BETA-CASEIN IN HUMAN-MILK BY MICROPARTICLE-ENHANCED NEPHELOMETRIC IMMUNOASSAY

A microparticle-enhanced nephelometric immunoassay was developed for b eta-casein quantification in human milk. It is based on the nephelomet ric measurement of the light scattered during the competitive immunoag glutination of a microparticle-human whole casein conjugate with an an ti-bovine beta-casein antiserum. This immunoassay is sensitive (detect ion limit in reaction mixture, 0.05 mg l(-1)) and can be performed in diluted milk (1:6000 in reaction mixture), excluding any interference or sample pre-treatment. It allowed the quantification of beta-casein over a large range of concentrations (0.6-18.3 g l(-1)) with accuracy (linear recovery in dilution-overloading assay) and precision (within- and between-run coefficients of variation from 3 to 12%). The develope d immunoassay was applied to the measurement of beta-casein concentrat ion in 230 human colostrum, transitional and mature milk samples. In t his preliminary study, the concentration was found to be significantly higher in transitional milk (3.1 g l(-1)) than in colostrum (2.2 g l( -1)). The ratio of beta-casein versus total protein was lower in colos trum (11%) than in transitional (23%) and in mature milk (22%).