Abstract: In order to improve the utilization of soybean proteins, soybean glycinin (11S) and β-conglycinin (7S) were subjected to ultrasound pretreatment before hydrolysis in this study, and then the structural changes of ultrasound treated and untreated 7S and 11S hydrolysates were studied by fluorescence spectroscopy, Fourier transform infrared spectroscopy and ultraviolet-visible absorption spectroscopy. The results showed that the secondary and tertiary structures of 7S and 11S hydrolysates were partially unfolded. Compared with the control, both treated 7S and 11S hydrolysates showed an increase in α-helix and β-turn proportions, and a decrease in β-sheet and random coil proportions, which suggested that the hydrophobic groups inside molecules were exposed to the surface. Moreover, ultrasonication significantly increased the degree of hydrolysis of 7S and 11S hydrolysates (P < 0.05) than the untreated controls. The antioxidant activity of the treated 7S and 11S hydrolysates demonstrated a significant improvement in reduction capacity, hydroxyl free radical scavenging activity and iron chelating capacity as compared to their respective untreated counterparts. Therefore, ultrasound pre-treatment is an effective way to enhance the hydrolysis of 7S and 11S to prepare hydrolysates with high antioxidant activity. These results can provide theoretical support for the development of natural antioxidant substances from soybean protein.

Key words: glycinin, β-conglycinin, enzymatic hydrolysis, structure, antioxidant activity