Evaluating the antioxidant capacity in different fraction of sheep milk.

The aim of the study was to design a protocol to evaluate sheep milk oxidation traits, both in the water soluble and the lipid soluble fractions, in order to assess such parameters in a simple and inexpensive way. Milk was fractioned as whole milk (WM), skim milk (SM), whey (W)) and deproteinated whey (DW). The antioxidant activity (TAC and AOP), available sulphydryls (SH), ascorbic acid (AA) and cholesterol content were determined, and the degree of antioxidant protection (DAP) of cholesterol was calculated. It was shown that current analytical methods should not be directly applied to milk, due to turbidity and peculiar pH behaviour of caseins. Therefore, samples may need some preparative steps before analysis. Proteins were found to account for most part of milk antioxidant capacity, with caseins playing the major role in milk antioxidant barrier. Such activity could not be attributed to available sulfhydryls (i.e. cysteine residues), suggesting a relevant contribution of other amino acids. The TAC method could be successfully applied for an overall estimation of both water and lipid soluble antioxidant activity of milk. However, peculiar classes of antioxidants, that are present at low concentrations, such as SH groups and AA may need more specific analytical techniques. Sheep milk (antioxidant capacity)