Evaluation of conformational and functional properties of covalent and non-covalent RBPI-CC complexes

This work investigated the binding interaction between (+)-catechin (CC) and rice bran protein isolate (RBPI) by determining the structure and function. The binding methods were covalent and non-covalent with different CC concentrations (0.05, 0.15, and 0.25%). Compared with non-covalent interactions, CC was more likely to form covalent interactions with RBPI. Additionally, the oligomers were formed during the covalent interactions of protein to CC. The results showed that CC reduced the ɑ-helices and β-sheets of the protein, and increased β-turns and random coils. The content of SH group contents decreased with the increase of CC concentration. Since in the covalent interactions at pH 9.0, the negatively charged quinonoid forms of CC will neutralize the positively charged protein, so the absolute ζ-potential will increase. The covalently linked RBPI-CC complexes have a smaller particle size. It can be seen from the microscopic image that the protein forms become more granular through the covalent action of CC. In this contribution functional properties were obtained by emulsifying activity index (EAI), emulsifying stability index (ESI), water holding capacity (WHC) and fat holding capacity (FHC). The WHC and FHC exhibited noticeable improvement, especially when the covalent interactions concentration of CC was 0.15%. Additionally, CC effectively increased the antioxidant activity of RBPI. This study is advantageous to elucidate the mechanisms underlying the interactions of CC with RBPI and the possible uses of RBPI-CC complexes in food formulations.