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 α s1 -cn fraction, which was 21.8% of the total cn fraction, whereas the β-cn percentage of total cn was 43.8%.The respective values for α s2cn and κ-cn were 13.7% and 13.8%.These quantitative characteristics were consistent with the predominance of the strong α 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 α 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 β-cn forms were variants A and C in similar frequencies.Variant D (formerly B) of κ-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.