Study on the mechanism of various exogenous proteins with different inhibitions on wheat starch digestion: From the distribution behaviors of protein in the starch matrix

This study aimed to compare the effect of various exogenous proteins on wheat starch (WS) digestion and assess the relevant mechanisms based on the distribution behaviors of exogenous proteins in the starch matrix. Rice protein (RP), soy protein isolate (SPI), and whey protein isolate (WPI) all effectively suppressed the rapid digestion of WS but with different modes. RP increased the slowly digestible starch content, while SPI and WPI increased the resistant starch content. Fluorescence images showed that RP aggregated and competed for effective space with starch granules, while SPI and WPI formed continuous network structures among the starch matrix. These distribution behaviors endowed different reductions in starch digestion by influencing the gelatinization and ordered structure of starch. Pasting and water mobility results suggested all exogenous proteins inhibited the water migration and swelling of starch. Simultaneously, X-ray diffraction and Fourier transform infrared spectroscopy analysis showed that exogenous proteins improved the ordered structures of starch. RP had a more significant effect on the long-term ordered structure, while SPI and WPI had a more effective effect on the short-term ordered structure. These findings will enrich the theory of exogenous protein inhibiting starch digestion and inspire the applications in low-glycemic index food.