The interaction of cocoa polyphenols with milk proteins studied by proteomic techniques

•The interaction of cocoa polyphenols with milk proteins was studied by proteomics.•Formation of a covalent complex with cocoa phenols was observed in beta-lactoglobulin.•The impact of other polyphenol/protein non-covalent interactions was also evaluated.•The data may explain the antioxidant properties of polyphenols in milk/cocoa drinks.

The molecular interaction of cocoa polyphenols with milk proteins were investigated in vitro by combined proteomic and biochemical strategies. Mass spectrometry and antioxidant activity assays allowed monitoring the binding of casein and whey protein fractions to cocoa polyphenols. In particular, the nature of interaction of β-lactoglobulin (β-Lg) with catechin and epicatechin was characterized and the amino acid residue at the binding site was identified. On the other side, antioxidant activity assays also showed a significant effect of the various milk protein fractions in decreasing the in vitro antioxidant activity of polyphenols, suggesting the existence of other types of protein-polyphenol interactions, probably weaker non-covalent bonds. From a nutritional point of view, these data indicate that the β-Lg covalent modification by polyphenol alone do not support the hypothesis of a decrease in the bioavailability of polyphenols themselves (Scalbert & Williamson, 2000). This might also explain the maintenance of the antioxidant properties of cocoa polyphenols in cocoa-based beverages. These results suggest the perspective use of the model system developed to study other complex food matrices.