Interaction characterization of preheated soy protein isolate with cyanidin-3-O-glucoside and their effects on the stability of black soybean seed coat anthocyanins extracts

The interactions of soy protein isolate with cyanidin-3-O-glucoside were investigated to study the protective effect of protein on anthocyanin's stability by UV-Vis spectrophotometry, Fourier transform infrared spectroscopy, circular dichroism and fluorescence spectroscopy. Preheat treatment and binding of cyanidin-3-O-glucoside effectively changed the secondary structure of soy protein isolate, with a decrease in alpha-helix, random coli structure and an increase in beta-sheet and beta-turn. The soy protein isolate preheated at 121 degrees C exhibited a strong binding affinity towards cyanidin-3-O-glucoside with strong Ks of 147.40 x 10(4)M(-1) and also effectively increased the thermal and oxidation stabilities of black soybean seed coat extract via decreasing the degradation rate by 67% and 23%, respectively. Soy protein isolate interacted with cyanidin-3-O-glucoside mainly through hydrophobic interactions and static quenching process. Altogether, the results suggested that preheated soy protein isolate-cyanidin-3-0-glucoside interaction could effectively protect anthocyanins' stability through strong binding affinity influenced by the systematic alterations in the secondary structure.