Investigation the interaction between quinoa glycopeptides and polyphenol: spectroscopic analyses and antioxidant activities

The interaction between quinoa glycopeptides (QGs) and three polyphenols [(−)-epigallocatechin-3-gallate (EGCG), gallic acid (GA) and tannic acid (TA)] was investigated by particle size, potential, fluorescence spectrum, and Fourier infrared spectrum, and the changes of antioxidant activity after compound were investigated by in vitro antioxidant experiments. The results showed that the average particle size of quinoa glycopeptide decreased and its distribution became more uniform after it was combined with three polyphenols. The intrinsic fluorescence was quenched and decreased with the increase of polyphenol content, and the maximum emission wavelength of the intrinsic fluorescence spectrum was redshifted. When combined with EGCG, GA and TA, the surface hydrophobicity of quinoa glycopeptides decreased significantly. The quenching type of EGCG, GA, and TA on quinoa glycopeptides was static quenching. The addition of polyphenols changed the hydrophobic amino acid groups in quinoa glycopeptides, and the hydrophobic interaction was the main force. Additionally, the secondary structure of QG was slightly changed after the binding of polyphenols to QG. Moreover, DPPH and ABTS radical scavenging abilities and ferric reducing antioxidant power analysis showed that EGCG, GA, and TA enhanced significantly the antioxidant capacity of QG. Therefore, this study can guide the preparation of quinoa functional food.