Casein diversity in caprine milk and its relation to technological properties: heat stability

Caprine milk is characterized by a genetically linked diversity in casein content. Of particular importance is the genetic polymorphism of α_s1-casein, which is under the influence of seven known alleles controlling the level of α_s1-casein expression in milk. In this article, the effect of α_s1-casein genotype on milk composition and heat stability is considered. Two different types of caprine milk were used: milk high in α_s1-casein from animals heterozygous AE or BE with respect to α_s1-casein genotype and milk low in α_s1-casein from animals homozygous FF. Milk high in α_s1-casein was less stable upon heating than milk low in α_s1-casein. Unlike bovine milk there was no recovery in heat stability at pH values greater than 7.0. These differences were associated with factors in the serum rather than the casein fraction and could not be explained by the variation in the protein composition, /3–lactoglobulin to casein ratio or the small variation in Ca²⁺ and lactose levels between the two milks. On the other hand, milk low in α_s1-casein had a higher urea content, which had a significant stabilizing effect.