Insight into the interaction mechanism between mulberry polyphenols and β-lactoglobulin

The interaction mechanism of components in complex food systems is one of the hot topics in food science. Both protein and polyphenols co-exists in many foods, but their interaction mechanism is very difficult to elucidate. In this paper, the interaction between mulberry polyphenols (MP) and β-lactoglobulin (β-LG) was investigated based on individual phenolic ratios in MP to explore impact of MP on β-LG. The results showed that the effects of MP on β-LG could be reproduced by simulated MP (sMP) which was composed of the main individual phenolics in MP. MP, sMP and individual phenolics interacted with β-LG through static quenching, in which MP, sMP, cyanindin-3-rutinoside (C3R) and epicatechin (EC) bound to β-LG via hydrogen bonds and van der Waals force; cyanindin-3-glucose (C3G) and p-coumaric acid (PCA) bound to β-LG via hydrogen bonds and hydrophobic interactions; but quercetin (Q), rutin (R), protocatechuic acid (PA) and pelargonidin-3-glucosid (Pg3G) bound to β-LG mainly through hydrophobic interaction. Addition of MP, sMP or most individual phenolics of MP significantly increased the particle size of β-LG. C3G, C3R, PCA, Q and R, with varying degrees of influence, markedly changed secondary structure of β-LG by affecting the microenvironment of amino acids residues. Furthermore, R, PCA, EC and Pg3G induced the transition from β-fold to α-helix of β-LG, making the protein more stable. The contribution of each individual phenolic to the interaction between MP and β-LG was mainly dose-dependent and also influenced by their chemical structures.