Roles of soybean β-conglycinin subunit fractions in fibril formation and the effects of glycinin on them

This research is aimed at exploring the fibrillation of soybean beta-conglycinin (7S) subunits (alpha alpha ' and beta) at 90 C and pH 2.0, as well as the effects of glycinin (11S) on them. Fibril formation kinetics was monitored by measuring changes in thioflavin T (Th T) fluorescence intensity of the proteins. This analysis showed that alpha alpha ' subunits had a higher fibrillation capacity but slower fibril formation rate than the beta subunit. Glycinin accelerated the rate of fibrillation of the alpha alpha ' and beta subunits but weakened the fibril structure. The size of the fibrils first decreased and then increased with increasing heating time. Circular dichroism and intrinsic fluorescence spectroscopy analysis indicated that the beta-sheet structure and hydrophobic interactions were important for the generation of ordered fibrils. Shear viscosity and transmission electron microscopy analysis suggested that the alpha alpha ' subunits formed relatively rigid fibrils that led to a high solution viscosity. In contrast, beta subunit fibrils became unstable after prolonged heating, forming shorter fibrils (fragments) that tended to aggregate, which led to a lower solution viscosity. This research also suggested that the extension region of alpha alpha' subunits played an important role in fibrillation, and the presence of the highly hydrophobic basic polypeptides of glycinin might be the main reason for the inhibition of soy protein fibrillation. Our analysis of soy protein fibrillization at the subunit level provides insights that might enhance the future application of soy protein fibrils as functional ingredients in foods.