Binding affinity between dietary polyphenols and beta-lactoglobulin negatively correlates with the protein susceptibility to digestion and total antioxidant activity of complexes formed

Abstract

Non-covalent interactions between beta-lactoglobulin (BLG) and polyphenol extracts of teas, coffee and cocoa were studied by fluorescence and CD spectroscopy at pH values of the gastrointestinal tract (GIT). The biological implications of non-covalent binding of polyphenols to BLG were investigated by in vitro pepsin and pancreatin digestibility assay and ABTS radical scavenging activity of complexes formed. The polyphenol-BLG systems were stable at pH values of the GIT. The most profound effect of pH on binding affinity was observed for polyphenol extracts rich in phenolic acids. Stronger non-covalent interactions delayed pepsin and pancreatin digestion of BLG and induced beta-sheet to alpha-helix transition at neutral pH. All polyphenols tested protected protein secondary structure at an extremely acidic pH of 1.2. A positive correlation was found between the strength of protein-polyphenol interactions and (a) half time of protein decay in gastric conditions (R-2 = 0.85), (b) masking of total antioxidant capacity of protein-polyphenol complexes (R-2 = 0.95).