Noncovalent interaction between proanthocyanidins and soy protein isolate fibers: Structure, functionality and interaction mechanism

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This study focused on the addition of different concentrations of proanthocyanidins (OPC) to form noncovalent complexes with soy protein isolate fibers (SPIF). To investigate the effects of polyphenols on the structural and functional properties of protein fibers and to elucidate the mechanism of their interaction. The addition of OPC unfolded the internal structure of the proteins, exposing the hydrophobic groups and reducing the β-sheet structure of SPIF, forming the SPIF-OPC complexes. And the binding of the two would be close to saturation, at the final concentration of added OPC was 0.5 or 1 mg/mL. Multiple spectroscopy and isothermal titration calorimetry analyses indicated that static quenching was the mechanism of fluorescence quenching of SPIF by OPC. The two spontaneously combined through hydrogen bonding and hydrophobic interactions. Transmission electron microscopy observations of the microscopic morphology also indicated that the addition of OPC altered the original long, semi-flexible fibers structure of SPIF. The fibers gradually showed a large number of branches and became short and curved. When the final concentration of added OPC was 4 mg/mL, the emulsifying activity index of SPIF increased by 78.40% and the foaming capacity of SPIF increased by 37.10%. The interaction mechanism of different concentrations of OPC with SPIF will be comprehensively understood from this study, thus expanding its application in food, medicine, cosmetics, and other fields.