Inhibitory effects of soy protein and its hydrolysate on the degradation of anthocyanins in mulberry extract

The inhibitory effects of soy protein (SP) and soy protein hydrolysate (SPH) on the changes in color and anthocyanin content in mulberry anthocyanin extract (MAE) during storage (42 °C/5 d) were investigated at pH 6.3. Fluorescence spectroscopy, circular dichroism (CD), and Fourier-transform infrared (FT-IR) spectroscopy were used to study the interaction between SP/SPH and cyanidin-3-O-glucoside (C3G), the major anthocyanin in MAE. The results showed that SP and SPH inhibited the degradation of color and anthocyanin content in MAE and extended its half-life (t1/2) 0.15 and 2.25 times, respectively. Additionally, the protection provided with SPH was better than with SP. The fluorescence analysis showed that SP and SPH interacted with C3G mainly through hydrophobic and electrostatic interactions, respectively, and the binding affinity of SPH for C3G was greater than that of SP. The inhibitory effect of SP/SPH on the degradation of MAE might be positively correlated with the SP/SPH–C3G interactions. FT-IR and CD results showed that complexation with C3G changed the secondary structure of SP/SPH, which was reflected by a decrease in the β-sheet content and increases in β-turns and random-coils. These results showed the efficacy of SP/SPH for preserving anthocyanins and developing functional, natural colorants for applications within the food industry.