Effect of mastitis on the lipid fraction of milk

Abstract

The effect of mastitis on the major lipid components of milk was investigated, using quarter milk samples from individual cows in the University herd. Milks with Wisconsin Mastitis Test (WMT) values < 10 mm were considered negative and those with WMT values > 20 mm positive for mastitis. The average fat globule size was not significantly altered by mastitis; however, the WMT positive milks contained more smaller (< 3.96 μ) fat globules. The WMT positive milks contained higher (P < 0.001) lipase activity and acid degree values and had 34.6% (P < 0.001) less phospholipids. Concentrations of total fatty acids were 4.0% lower (P < 0.001), and free fatty acids were 47.3% higher (P < 0.001) in WMT positive milks. The WMT positive samples had higher molar percentages of total fatty acids C[subscript 4:0] to C [subscript 14:0] and lower molar percentages of C[subscript 16:0] and C[subscript 18:0]. Molar percentages of the free fatty acids C[subscript 4:0], C[subscript 8:0], C[subscript 10:0], C[subscript 12:0], and C[subscript 14:0] were lower, while the molar percentages of C[subscript 16:0], C[subscript 16:1], C[subscript 18:0], C[subscript 18:1], and C[subscript 18:2] were higher in WMT positive milks. The WMT positive milks yielded 10.0% less (P < 0.05) milk fat globule membrane material. Higher (P < 0.01) amounts of aldolase and xanthine oxidase were present in the membrane preparation from WMT positive milks. The lipid moiety of the membrane preparation from WMT positive milks contained lower amounts of phospholipid (P < 0.05) and higher amounts of cholesterol per gram of membrane. Delipidated, dissociated membrane protein prepared from WMT positive milks was separated into five components by polyacrylamide gel electrophoresis, while the membrane protein prepared from WMT negative milks was separated into three components.