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

Abstract

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 α-helix, random coil structure and an increase in β-sheet and β-turn. The soy protein isolate preheated at 121 °C exhibited a strong binding affinity towards cyanidin-3-O-glucoside with strong Ks of 147.40 × 10⁴ 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-O-glucoside interaction could effectively protect anthocyanins' stability through strong binding affinity influenced by the systematic alterations in the secondary structure.

Keywords: Anthocyanins; Black soybean; Cyanidin-3-O-glucoside; Cyanidin-3-O-glucoside (PubChem CID: 185664); Disodium hydrogen phosphate (PubChem CID: 71180); Hydrochloric acid (PubChem CID: 313); Hydrogen peroxide (PubChem CID: 784); Interaction; Potassium bromide (PubChem CID: 253877); Potassium chloride (PubChem CID: 4873); Sodium acetate (PubChem CID: 517045); Sodium dihydrogen phosphate (PubChem CID: 24204); Soy protein isolate; Stability; Tryptophan anion (PubChem CID: 3090777); Tyrosine cation (PubChem CID: 5460804).