Antioxidant activity of ovine casein hydrolysates:: identification of active peptides by HPLC-MS/MS

This paper shows the potential role of different ovine casein fractions and their hydrolysates to exert antioxidant activity. ABTS(-+) decolorization assay was used to evaluate the antioxidant activity of the casein fractions (beta-, kappa- and alpha(s)-caseins) before and after their hydrolysis by pepsin, trypsin and chymotrypsin. Although the antioxidant activity increased in all the fractions after hydrolysis, the effect was particularly remarkable in the kappa-casein fraction, which increased its antioxidant activity almost threefold. Further assays in a linoleic acid oxidation system showed that kappa-casein hydrolysate inhibited lipid peroxidation. Analysis of the ovine kappa-casein hydrolysate by RP-HPLC-MS/MS allowed the identification of 12 peptide sequences with potential antioxidant properties. One of the most abundant peptides, the fragment HPHPHLSF [f(98-105)] was chemically synthesized. Results showed that this kappa-casein-derived peptide was a potent inhibitor of linoleic acid oxidation with an activity similar to that obtained with the synthetic antioxidant BHT. Although other peptides might also contribute, HPHPHLSF was the one most likely to be responsible for the activity found in the kappa-casein hydrolysate.