Review:: Polymorphism of the caprine αs1-casein gene and its effect on the production, composition and technological properties of milk and on cheese making and ripening

The caprine alpha(s1)-casein gene displays a high degree of polymorphism, with eight different protein variants described up to date. The rate of synthesis of the mature protein is closely linked to the caprine alpha(s1)-casein genotype. There are three variants which are associated to high alpha(s1)-casein content in milk (A, B, and C), one to an intermediate content (E), three to a low content (D, F, and G) and one to a null content (O). During the last few years studies of goat milk protein polymorphism have gained renewed interest, as the ocurrence of certain milk protein genetic variants is correlated with the composititon of milk and also with some milk processing parameters. For instance, analyses of the physicochemical properties of milk from goats homozygous for the three main alpha(s1)-casein alleles (A, E, F) confirm the effects of the genotypes on the percentage of casein and fat, and shows significant effects on the diameter of the micelles and their calcium content. These characteristics seem to be associated with enhanced clotting of goat milk, cheese curd firmness, curd syneresis and overall cheese yield. The caprine alpha(s1)-casein gene constitutes a very attractive model for studying the regulation of the expression of the corresponding protein, and might also become a very powerful tool in improving the technological properties of goat milk.