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.

Automated summary

This study compared the effects of different exogenous proteins on wheat starch digestion and evaluated the mechanisms involved based on the distribution behaviors of the proteins in the starch matrix. Rice protein, soy protein isolate, and whey protein isolate all effectively inhibited the rapid digestion of wheat starch, but through different modes. Rice protein increased the content of slowly digestible starch, while soy protein isolate and whey protein isolate increased the content of resistant starch. Fluorescence images demonstrated that rice protein aggregated and competed for effective space with starch granules, while soy protein isolate and whey protein isolate formed continuous network structures within the starch matrix. These distribution behaviors resulted in varying reductions in starch digestion by influencing the gelatinization and ordered structure of starch. Pasting and water mobility results indicated that all exogenous proteins inhibited water migration and swelling of starch. Additionally, X-ray diffraction and Fourier transform infrared spectroscopy analysis revealed that the exogenous proteins improved the ordered structures of starch. Rice protein had a more significant effect on the long-term ordered structure, while soy protein isolate and whey protein isolate had a more effective effect on the short-term ordered structure. These findings will contribute to the understanding of exogenous protein inhibition of starch digestion and inspire applications in low-glycemic index foods.