Mechanistic studies of polyphenols reducing the trypsin inhibitory activity of ovomucoid: Structure, conformation, and interactions

The present study was aimed to evaluate the interaction between anthocyanins from black rice and soybean protein isolate (SPI) via non-covalent and covalent bindings and the impact of these interactions on the functional and conformational changes of soybean protein. The conformational changes of the protein structure with different concentrations of anthocyanins (0.05, 0.1%, and 0.2%) were analyzed using three-dimensional fluorescence and Fourier transform infrared spectroscopy. The anthocyanins were more likely to form covalent interactions with SPI instead of non-covalent interactions. The addition of anthocyanins changed the secondary structure of SPI with a decrease in β-sheets and an increase in β-turns and random coils. The emulsifying and foaming properties of SPI were improved after complexation with anthocyanins. This study might be useful for elucidating the mechanisms behind the binding of anthocyanins with SPI and the possible uses of SPI-anthocyanin complexes in food formulations.

Several health benefits have been ascribed to consumption of resveratrol, a polyphenol that can be extracted from grape skins. However, its use as a nutraceutical ingredient is compromised by its low water solubility, chemical stability, and bioavailability. Encapsulation of resveratrol in protein nanoparticles can be used to overcome these issues. Fluorescence quenching experiments were used to study the interaction of resveratrol with gliadin and zein. Resveratrol interacted with both proteins, but the binding constant was higher for zein than for gliadin at 35 °C. Furthermore, binding between resveratrol and gliadin increased at higher temperatures, which was not observed for zein. Analysis of the thermodynamic parameters suggested that resveratrol-gliadin binding mainly occurs through hydrophobic interactions while the binding with zein is predominantly mediated through hydrogen bonds. These results help rationalise ingredient selection and production of protein nanoparticles and microparticles for encapsulation, protection and release of resveratrol and potentially other bioactive compounds.