Effect of non-covalent and covalent complexation of (−)-epigallocatechin gallate with soybean protein isolate on protein structure and in vitro digestion characteristics

The present study was aimed to investigate the effects of non-covalent and covalent interactions between soy protein isolate (SPI) and different concentrations (1, 2 and 5 mM) of (−)-epigallocatechin gallate (EGCG) regarding the structural and functional properties of the complex. The combination with EGCG caused changes in the secondary structure of SPI. The covalent complexes formed at low concentrations of EGCG tended to form a network structure. Compared with the SPI-EGCG non-covalent complexes, the covalent complexes exhibited higher thermal stability and oxidation resistance and a polyphenol-protective effect. In addition, the corresponding anti-digestive ability of the covalent complexes was strong and would therefore be more stable in the intestinal tract. The findings of this study provide a theoretical reference and research basis for the use of different SPI-polyphenol complexes as functional food ingredients or as bioactive materials.