Stability of buffalo casein micelles.

Buffalo skim-milk is less heat stable than cow skim-milk. Interchanging ultracentrifugal whey (UCW) and milk diffusate with micellar casein caused significant changes in the heat stability of buffalo casein micelles (BCM) and cow casein micelles (CCM). Buffalo UCW dramatically destabilized CCM, whereas buffalo diffusate with CCM exhibited the highest heat stability. Cow kappa-casein stabilizes alphas-casein against precipitation by Ca better than buffalo kappa-casein. About 90% of alphas-casein could be stabilized by kappa:alphas ratios of 0.20 and 0.231 for cow and buffalo, respectively. Sialic acid release from micellar kappa-casein by rennet was higher than from acid kappa-casein in both buffalo and cow caseins, the release being slower in buffalo. The released macropeptide from buffalo kappa-casein was smaller than that from cow kappa-casein as revealed by Sephadex gel filtration. Sub-units of BCM have less sialic acid (1.57 mg/g) than whole micelles (2.70 mg/g). On rennet action, 47% of bound sialic acid was released from sub-units as against 85% from whole micelles. The sub-micelles are less heat stable than whole micelles. Among ions tested, added Ca reduced heat stability more dramatically in whole micelles, whereas added phosphate improved the stability of micelles and, more strikingly, of sub-micelles. Citrate also improved the heat stability of sub-micelles but not of whole micelles.