Effects of Polyphenols from Walnut Pellicles on the Structure and Allergenicity of Walnut Globulin

In this study, we explored the effects of polyphenols from walnut pellicles on the structure and allergenicity of walnut protein. The combination with polyphenols from pellicles affected structural profiles that characterized by UV-Visible, fluorescence, FTIR and CD spectroscopy and significantly (P<0.05) reduced Immunoglobulin G (IgG)-binding capacity of walnut protein. Additionally, allergenicity-guided assay revealed walnut globulin (WG) was the main allergenic protein, binding to polyphenols altered morphological structure and significantly (P<0.001) decreased allergenicity of WG. Furthermore, complexes of phenolic extracts from walnut pellicle (PEWP) and WG prepared in neutral and alkaline pH conditions were characterized and the interaction between them was investigated using multi-spectroscopy, indicating combination between PEWP and WG was affected by the ratio and pH value. Multi-spectroscopic analyses reveled that combination of polyphenols and protein caused a decrease in fluorescence intensity and α-helix content, and an increase in β-turn and random coil contents, leading to the unfolding of the protein structure. Meanwhile, combination with PEWP reduced the IgG-binding capacity of WG in a dose-dependent manner, reaching the lowest of 26.90±4.31% (at pH 7), which was significantly (P<0.05) lower compared to that at pH 11 (41.79±1.25%). Correlation analysis indicated that IgG-binding capacity had a significant correlation with protein structure and adding concentration of PEWP (r= -0.85, P<0.01), and pH conditions may indirectly affect the structure and allergenicity of protein by influencing the interaction between WG and PEWP. Moreover, fluorescence-quenching mechanism analyses revealed interaction between WG and PEWP mainly occurred through hydrogen bond and hydrophobic interaction at pH 7.