Ultrasound-assisted preparation of faba bean protein isolate-Vitis vinifera L. polyphenol extract conjugates: Structural and functional characterization

The purpose of this study was to create conjugates between faba bean proteins (FP) and grape leaf polyphenols (GLP) utilizing an alkaline treatment assisted by sonication. The effects of sonication intensity on the binding of FP and GLP were investigated using scanning electron microscopy (SEM), Fourier Transform Infrared (FT-IR) spectroscopy and differential scanning calorimetry (DSC). The SEM results revealed that sonication altered the structure of the solid material formed by dehydrating FP-GLP conjugates, with fragmented particles being observed in the powdered form. The FTIR results showed that sonication increased the β-sheet structure content while decreasing the α-helix and β-turn structure content. Sonication decreased the size of the FP-GLP conjugates, which was attributed to disruptive cavitation and shear forces. The magnitude of the zeta potential of the conjugates increased significantly after sonication, which suggested that it induced some chemical alterations of the functional groups on the proteins and/or polyphenols. The antioxidant and emulsifying activities of the conjugates were also altered appreciably by sonication. Overall, the effects of sonication depended on the degree of sonication used, which should therefore be optimized to obtain conjugates with the desired functional attributes. This study showed that sonication reduced the production time from 24 h to 10 min of FP-GLP conjugates and enhanced their antioxidant (increased DPPH and ABTS, 145.89% and 48.08%) and emulsifying properties might be beneficial as functional components in foods and other industrial items.