Interaction of Protein Isolate with Anthocyanin Extracted from Black Soybean and Its Effect on the Anthocyanin Stability

The interactions between black soybean protein isolate (B-SPI) and cyanidin 3-O-glucoside (C3G), anthocyanin extracted from black soybean coat was investigated under neutral conditions. The fluorescence spectra showed that C3G had fluorescence quenching effects on B-SPI. Thermodynamic parameters showed that increment G < 0, which demonstrated that the binding was a spontaneous reaction. Since Delta H > 0 and Delta S > 0, the interactions between C3G and B-SPI was mainly hydrophobic interactions. Fourier infrared spectroscopy results suggested that the contents of alpha-helix and beta-sheet structure showed an increasing trend, whereas the beta-angle content displayed a decreasing trend. The degradation of C3G followed first-order kinetics at 85 degrees C and 100 degrees C. After the interactions with B-SPI, the degradation rate constant was decreased and the half-life of C3G was prolonged from 70.25 +/- 0.90 min to 175.64 +/- 38.04 min at 85 degrees C, from 62.68 +/- 1.1 min to 72.51 +/- 2.5 min at 100 degrees C (p < 0.05). The results indicated that the interactions of B-SPI and C3G improved the thermal stability of C3G under heating conditions.