Protein composition and polymorphism in the milk of Skopelos goats

Individual milk samples taken from goats of the Skopelos breed of Greece were analyzed by RP-HPLC using as standards the casein fraction of milks of known genotypes. Milk samples with particular characteristics with respect to the casein fraction were further analyzed by IEF and RP-HPLC/ESI-MS. The mean total protein content (36.7 +/- 2.6 g . L-1) and the mean casein content (29.7 +/- 2.3 g . L-1) were high. The same was true for the alpha(s1)-cn fraction, which was 21.8% of the total cn fraction, whereas the beta-cn percentage of total cn was 43.8%. The respective values for alpha(s2)-cn and kappa-cn were 13.7% and 13.8%. These quantitative characteristics were consistent with the predominance of the strong alpha(s1)-cn variants B3, B4 and As/B1. In all samples analyzed by RP-HPLC/ ESI-MS the deleted form differing from the respective complete form by Gln78 was found at different levels of phosphorylation, with the exception of variants F and D/G. The most frequent alpha(s2)-cn variant was by far variant A followed by variants C and F, whereas compositional data implied the existence of a null allele. The detected beta-cn forms were variants A and C in similar frequencies. Variant D ( formerly B) of kappa-cn predominated and the rare variant G was found. Different phosphorylation types of each casein variant and the characteristics of whey proteins were also determined.