Covalent interaction of soy protein isolate and chlorogenic acid: Effect on protein structure and functional properties

Covalent interaction of soy protein isolate (SPI) and chlorogenic acid (CA) through laccase catalysis was studied. The structure, interfacial properties (foaming and emulsifying properties) and antioxidant activities of soy protein isolate-chlorogenic acid (SPI-CA) adducts were characterized. The formation of covalent adducts was indicated by the result of the SDS-PAGE analysis. The UV–vis and FTIR analysis indicated that the addition of CA resulted in changes in the secondary structure of the protein. The spectroscopy analysis indicated that the structure of SPI tended to unfold. The emulsifying activity of SPI-CA80 (CA concentration is 80 μmol/g protein) adducts was the highest, which increased by 34.77%. Additionally, SPI-CA100 adducts exhibited high antioxidant capacity, with ABTS and DPPH radical scavenging rates increased by 24.83% and 14.41%, respectively. The results showed that the interfacial properties of SPI were correlated with changes in the concentration of CA. Overall, this study demonstrates that covalent binding of SPI to CA enhances the potential application of SPI as a functional ingredient in food.