Relationship between αs1-casein variants and clotting capability of ovine milk

Five ovine alpha(s1)-casein variants, for example A, B, C, D, and E, have been detected in Italian ovine milk. Since studies on aptitude of Sarda breed for cheesemaking have shown the poorest clotting capability of D variant, a study was carried out to investigate the effect of alpha(s1)-casein polymorphism on the clotting profile of ovine milk. A total of 87 individual milk samples belonging to Sarda x Comisana, Sarda x Delle Langhe, and Comisana x Delle Langhe sheep crossbreeds were analysed for fat, protein, casein content, thromboelastographic parameters, for example r (min), k(20) (min), and 2r (mm), and for alpha(s1)-casein phenotype. AC, BB, CC, BC, and CD alpha(s1)-casein phenotypes occurred with a frequency of 3.4, 1.1, 41.3, 51.7 and 6.8%, respectively. Only milk containing alpha(s1)-casein CC, CD and BC was compared for technological behaviour. Milk production was found to decrease in the order BC>CC>CD. Fat, total N (P<0.05), and casein content (P<0.05) of the CC containing milks were higher than for both CD and BC. By comparing the ability of each phenotype to form a well-structured curd, CC was found superior to BC (P<0.05). Although not directly examined, we presume that the BB phenotype shows thromboelastographic parameters similar to those of BC and CD. Among the three phenotypes studied, the D variant was confirmed to be detrimental to ovine milk, even in association with other variants.