The effects of the interaction between cyanidin-3-O-glucoside (C3G) and walnut protein isolate (WPI) on the thermal and oxidative stability of C3G

This study explores the interaction between cyanidin-3-O-glucoside (C3G), a water-soluble pigment known for its diverse functional activities, and walnut protein isolate (WPI) as a potential stabilizing agent. Given the inherent instability of C3G, particularly its limited application in the food industry due to sensitivity to thermal and oxidative conditions, this research study aims to enhance its stability. According to the results of the fluorescence quenching experiment, C3G can efficiently quench WPI's intrinsic fluorescence through static quenching. Structural exploration revealed that C3G bound WPI via hydrophobic interaction force, with the number of bound C3G molecules (n) almost equivalent to 1. The ΔG value denoting change in Gibbs free energy for C3G binding with WPI was -8.05 kJ/mol, which indicated that the interaction between C3G and WPI is spontaneous. Moreover, the conformational structures of WPI were altered by C3G binding with a decrease in α-helix contents and an increase in β-turn, β-sheet, and random coil contents. The thermal degradation kinetics indicate that after interacting with WPI, the half-life of C3G increased by 1.62 times and 1.05 times at 80 and 95°C, respectively. The results of the oxidation stability test showed that the presence of WPI effectively reduced the discoloration and degradation of C3G caused by oxidation, and improved the oxidation stability of C3G. This study's findings will help to clarify the interaction mechanism between C3G and WPI, and broaden C3G's application scope in the food processing field.