The composition, size and hydration of yak casein micelles

The composition, size and hydration of yak (Bos grunniens) casein micelles and the variation of these parameters during a warm and a cold period, were investigated. The concentrations of micellar calcium, magnesium and inorganic phosphorus in yak milk obtained during the cold period were higher than those obtained during the warm period, while the reverse result was observed for micellar citrate. In yak casein micelles, the relative proportion of beta-casein decreased significantly from the warm period to the cold period, whereas the opposite was observed for alpha(S1)-casein, and the relative proportion of alpha(S2)- and kappa-casein remained largely constant. Casein micelles in yak milk obtained during the cold period showed smaller average diameter, narrower size distribution and higher hydration. On the other hand, these parameters of casein micelles in yak milk differed significantly compared with those in cows' milk, with different contents of the components, larger average size and higher hydration. (C) 2013 Elsevier Ltd. All rights reserved.