Influence of mastitis on the properties of bovine caseins

Abstract

The effect of mastitis on the distribution and properties of the native casein micelles and the isolated casein fractions of skimmilk was investigated. Quarter milk samples were obtained from individual cows and analyzed by the Wisconsin Mastitis Test (WMT). Samples with WMT values < 10 mm were considered negative (normal) while those with WMT values > 20 mm were regarded positive (abnormal) for mastitis. Approximately 71 to 94% of the casein was sedimented from normal skimmilk compared to 51 to 78% from abnormal skimmilk, following ultracentrifugation at 56,000 to 144,000 x g for 1 hr at 4 C. About 50% of the proteins were destabilized in abnormal skimmilk compared to 10% in normal skimmilk by heating at 90 C for 10 min. Dialyses of abnormal against normal skimmilk (1:10 v/v ratio) for 36 hr at 4 C considerably increased both protein stability and casein sedimentation in abnormal skimmilk. Both normal and abnormal skimmilks were fractioned into four components by Sephadex G-100 and no significant differences were apparent in the elution patterns. The concentration of soluble and micellar casein in milk was dependent on calcium concentration, pH, and temperature. In all cases, abnormal skimmilk contained less micellar and more soluble casein than normal skimmilk. Mastitis induced significant changes in the composition and properties of milk proteins. ...