Non-covalent interaction of the plant protein composites-proanthocyanidins and the utilization in oil in water emulsions

The polyphenols and plant proteins are increasingly being utilized as functional food ingredients, it is critical to understand their interaction mechanism with each other. In this study, protein composites (RP-PP and RP-SPI) were fabricated using pH-driven technology by rice protein (RP) with pea protein (PP) and soy protein isolates (SPI), respectively. The interaction mechanism between the protein composites and proanthocyanidins (PA) was also explored using a combined approach of spectroscopy and thermodynamics. The analysis of fluorescence spectroscopy and turbidity confirmed the formation of the protein composites-PA colloidal complexes. The thermodynamic results calculated from fluorescence data and ITC analysis indicated the hydrogen bond was the main interaction force between the protein composites and PA. The secondary structures of the protein composites were changed with the decreased α-helix and β-turn due to the increasing PA. In addition, the existence of PA reduced the surface hydrophobicity, particle size, and the interfacial tension of proteins. Furthermore, the thermal stability and zeta potential of proteins increased after the binding of the PA. Ultimately, the PA showed a potential in reducing the dimension of droplet and enhancing storage stability of proteins-PA emulsion. This study provides useful information for the industrial application of the proteins-polyphenols complexes.