Effects of Milk Composition and Genetic Polymorphism on Coagulation Properties of Milk

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Abstract
Milk samples from 31 Holstein cows of different phenotypes for .beta.-casein, .kappa.-casein, and .beta.-lactoglobulin were collected monthly over the entire lactation. These samples were analyzed for total solids, fat, protein, casein fractions, lactose, urea, citric acid, somatic cell count, and pH. Rennet clotting time, rate of firming, and curd firmness as measured by a Formagraph were not significantly influenced by phenotypes for .beta.-casein and .kappa.-casein. Phenotype AA for .beta.-lactoglobulin gave the best clotting time (3.91 min) and firmness of curd (36.30 mm) when compared with AB and BB phenotypes. Relative percentages of the different caseins and .alpha.-lactalbumin affected significantly rate of firming and curd firmness at cutting. Amount of .kappa.-casein in milk was the most significant factor that affected curd firmness with a coefficient of regression of 15.96.