Effect of anionic polysaccharides on conformational changes and antioxidant properties of protein-polyphenol binary covalently-linked complexes

[Display omitted] •Anionic polysaccharides were added to interact with the covalently-linked complexes.•The interaction is through steric hindrance and electrostatic repulsion.•Compared the effects of CMC or pectin on the binary complexes.•Complexes emulsion with pectin added had better stability and antioxidant activity. This work evaluated the anionic polysaccharides to improve the functional properties and antioxidant activities, and compared the effects on covalently-linked the soy protein isolate (SPI)- (–)-epigallocatechin-3-gallat (EGCG) binary complexes. The increasing molecular weight via covalent insertion of (–)-epigallocatechin-3-gallat (EGCG) into the soy protein isolate (SPI) was verified by SDS-PAGE. The addition of polysaccharides had no obvious effects on the molecular weight, indicating noncovalent insertion by adsorption. Fourier transform infrared spectroscopy (FT-IR) analysis suggested that SPI-EGCG complexes mixed with polysaccharides changed the secondary structures of SPI with a decrease in α-helix and an increase in β-turn. The emulsions exhibited better stability index (ESI) by adding polysaccharides than the binary complexes emulsion, with decreased particle sizes and increased absolute ζ-potential values, while the value of ESI for the pectin mixed increased more. The 1,1-diphenyl-2-picrylhydrazyl radical (DPPH•) scavenging capacity of SPI-EGCG complexes with the addition of polysaccharides were both greater than 70 %. These findings indicated that anionic polysaccharides could be potentially used as a natural and safe alternative for regulating covalently-linked SPI-EGCG emulsion stability and improving emulsion oxidation resistance.