Interaction between soybean protein and tea polyphenols under high pressure

Tea polyphenols (TP) and soybean proteins (SP) are important materials in food industry. High hydrostatic pressure (HHP) is a useful tool for improvement of protein's function. This study evaluated the interactions between the polyphenol and HHP-treated protein using circular dichroism, fluorescence spectroscopy and molecular modeling. The high pressure at 400 MPa significantly modified the secondary structure of SP by increasing the beta-sheet content and decreasing the alpha-helix content, while the addition of 0.1% (w/v) tea ployphenol appeared to protect the alpha-helix structure. The surface hydrophobicity decreased with HHP treatment and the addition of TP. The optimal solubility of native SP was 0.258 g/mL at 0.08% (w/v) TP. Together with HHP treatment; TP increased the protein solubility to 0.50 g/mL and the emulsifying activity was enhanced approximately three times, up to 43.5%. The micro-texture of SP matrix was also improved with TP and HHP treatment. Both the hydrogen bonding and hydrophobic interaction between TP and SP were elucidated using docking method. Apart from the hydrogen bonding, the Pi-Pi interaction was observed in the binding of phenolic compounds to 7S or 11S globular protein.