Size of native and heated casein micelles, content of protein and minerals in milk from Norwegian Red Cattle -: effect of milk protein polymorphism and different feeding regimes

Milk samples of 59 cows of the Norwegian Red Cattle breed receiving three different supplementary concentrates, were analysed for genotypes of caseins and whey proteins, the content of different milk salts (Ca2+, Ca, Mg and citrate), the content of total protein, casein and whey protein and the mean micellar size of native and heated casein micelles. The genotype of alpha(s1)-casein had a statistically significant effect on the content of protein and casein, and the content of whey protein and the casein number were significantly influenced by different feeding regimes, and the content of citrate. The mean size of native and heated casein micelles was significantly influenced by the feeding regimes, genotype of alpha(s1)-casein (native mean size only) and kappa-casein, pH and the content of casein, whey protein and casein number. The heat-induced changes in mean micellar size were significantly affected by the calcium ion activity which accounted for approximately 40% of the total variation. (C) 2000 Elsevier Science Ltd. All rights reserved.