Measurement of beta-casein in human milk by microparticle-enhanced nephelometric immunoassay
A microparticle-enhanced nephelometric immunoassay was developed for beta-casein quantification in human milk. It is based on the nephelometric measurement of the light scattered during the competitive immunoagglutination of a microparticle-human whole casein conjugate with an anti-bovine beta-casein antiserum.
This immunoassay is sensitive (detection 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 developed immunoassay was applied to the measurement of beta-casein concentration in 230 human colostrum, transitional and mature milk samples. In this 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 colostrum (11%) than in transitional (23%) and in mature milk (22%).