New insights into rice starch-gallic acid-whey protein isolate interactions: Effects of multiscale structural evolution and enzyme activity on starch digestibility

Abstract

In starch-based food where proteins and polyphenols coexist, the impact of protein on the inhibition of starch digestion by polyphenols is unclear. Therefore, the aim of this study was to investigate the impact of whey protein isolate (WPI) on the inhibition of rice starch digestion by gallic acid (GA) from the aspects of multiscale structure and enzyme activity. Rice starch-gallic acid-whey protein isolate complex (RS-GA-WPI) was formed predominantly by hydrogen bonding and hydrophobic interactions. Compared to rice starch-gallic acid complex (RS-GA), RS-GA-WPI exhibited higher short-range ordering and thermal stability, and lower relative crystallinity. Fluorescence spectra and molecular docking showed that the interactions between GA and WPI weakened the hydrogen bond between GA and enzyme active site, so that WPI significantly reduced the enzyme inhibitory activity of GA. The above factors led to the result that the presence of WPI weakened the inhibitory effect of GA on starch digestibility. RS-GA-WPI showed higher starch digestibility and lower resistant starch content compared to RS-GA. This study provided a new understanding of starch digestion mechanism in starch-polyphenol-protein coexistence system.