Conformational changes and functional properties of soy lipophilic protein-epicatechin complexes formed by non-covalent interaction

Soy lipoprotein (SLP) is the main component of soy protein isolate in addition to beta-conglycinin (7 S) and glycinin (11 S), The contents of 7 S, 11 S and SLP were 23%, 46% and 31%, respectively. It has the effect of reducing blood cholesterol and triglyceride and can be used as a good carrier for transporting conjugated linoleic acid. This study investigated the effect of the interaction between soy lipophilic protein (SLP) and epicatechin (EC) on protein structure, their binding mode, physicochemical and antioxidant activities. Different concentrations of epicatechin (0, 0.1, 0.2, 0.3, 0.4 and 0.5 mg mL(-1)) were used to interact with soybean lipophilic protein. Identification of the binding mode of SLP and EC was achieved by Fluorescence and Fourier transform infrared (FTIR) spectroscopy. It was revealed that epicatechin bound to SLP mainly through hydrophobic interaction. The addition of EC changed the secondary structure of SLP, decreased alpha-helix and random coil contents and increased beta-strand contents. Fluorescence spectrum analysis results showed that after the combination of SLP with EC, the tertiary structure of the protein became loose and the surface hydrophobicity decreased due to unfolding of the protein polypeptide chain. The emulsifying and antioxidant activities of SLP were improved after complexation with EC. This study provides clarifications on the mechanism of the formation of SLP-EC complex and provides a new avenue in developing new food carriers using plant proteins and polyphenols.