The influence of genetic variants of milk proteins on the compositional and technological properties of milk .1. Casein micelle size and the content of non-glycosylated kappa-casein

Milk samples (total = 203) containing different genetic variants of the milk proteins were analyzed for the average casein micelle diameter. In addition, most samples (n = 191) were analyzed for the content of nonglycosylated kappa-casein by IPG-IEF. Special attention was paid to the rare genetic variants (alpha(s1)-Cn C, beta-Cn B or C, and kappa-Cn C or E). There were highly significant (p<0.001) relationships between the genotypes of the beta-Cn, kappa-Cn and beta-Lg locus and the average diameter of the casein micelles. The kappa-Cn locus had the greatest influence on the average micelle size, which increased from 190 nm to 229 nm in the following order: kappa-Cn BC/BB<AB<AC<BE<AA<AE. A highly significant relationship (p<0.001) was also observed between the genotypes of the kappa-Cn locus and the content of non-glycosylated kappa-casein, which increased in the following order: AC/AE<AA<AB<BE<BC<BB. Milk of the type beta-Lg BB contained significantly more (p<0.05) non-glycosylated kappa-casein than the type beta-Lg AB and AA. The allele kappa-Cn B in the genotypes AB, BC and BE induced a significantly greater amount of non-glycosylated kappa-casein than the alleles A, C and E, whereas the A-allele induces significantly less non-glycosylated kappa-casein than the alleles B and E.