Oxidation of some milk lipid materials in model systems in presence of copper and ascorbic acid

Abstract

SummarySome milk lipid materials representing the phospholipid protein complex—fat globule membrane from buttermilk (FGMI) and from butter serum (FGMII), intact fat globules (dialysed cream) and triglycerides (butter oil)—were subjected to copper-induced oxidation in systems containing distilled water, phosphate buffer of pH 6·60 or milk dialysate. These model systems usually contained 2% lipid material and were allowed to oxidize for 48 h at 3–5 °C. Oxidation intensity was measured by means of the 2-thiobarbituric acid test.The oxidation intensity was dependent on the composition of the lipid material and of the aqueous phase. Ascorbic acid in absence of added copper catalysed the oxidation of the membrane materials and of globular fat. The oxidation intensity produced by FGMI (from buttermilk) differed significantly from that produced by FGMII (from butter serum) and the difference was well correlated with differences in their composition. Butter-oil preparations gave the lowest oxidation intensities, indicating that they are not the site for development of oxidative defects in aqueous media.