Oxidative stability of bovine milk determined by individual variability in herd irrespective of selenium status

The effect of supplementing dairy cows with organic selenium (25 mg day−1) on oxidative stability of milk when exposed to Cu(II) ions or to fluorescent light was evaluated using solid-phase micro-extraction gas chromatography with flame ionisation detection. Neither formation of volatile lipid (hexanal) and protein (dimethyl disulfide) oxidation products nor radical scavenging activity was affected by selenium supplementation. We found that other factors must be determinant for the oxidative stability of milk, and that these factors vary considerably between individual cows. Milk from two cows that were either sensitive or resistant to oxidation was compared in an attempt to identify the molecular basis for these differences. It was found that oxidation of milk could not solely be explained on the basis of fatty acid composition, or content of low molecular weight antioxidants, such as uric acid, ascorbic acid, and tocopherol.