Insights into wheat starch-soy protein isolate-tannic acid interactions: Effect of gelatinization and multiscale...

The structures of SPI and the thermodynamically incompatible conditions between starch and SPI limit the application of SPI in starch-based foods. This study employed tannic acid (TA) to modulate the affinity between wheat starch (WS) and SPI, thoroughly investigating the effects of interactions among WS, SPI, and TA on the structural and digestive properties of WS. The interactions among WS, SPI, and TA depended on the amount of TA, which influenced the structures of both WS and SPI. Low TA amount promoted the aggregation of SPI, enhancing the phase splitting between WS and SPI and inhibiting starch granules gelatinization and starch molecules retrogradation. Higher amount of TA would reduce the particle size of SPI, promoting the association between WS and SPI and increase WS granules gelatinization, but reduce WS molecules rearrangement through compete water with WS. However, the huge steric hindrance and the enhanced interactions among WS, SPI, and TA caused by excessive TA addition would reduce the rearrangement of WS molecules. Additionally, rising TA amount increased the V-type inclusion crystalline content within the complexes. Compared to the WS-SPI or WS-TA binary systems, the WS-SPI-TA ternary system exhibited lower short-range ordered structures but higher relative crystallinity and changed with TA amount. Moreover, the physical barrier provided by SPI and the inhibitory effects of TA, SPI, and SPI-TA complexes on amylolytic enzymes reduced enzyme activity. Consequently, the WS-SPI-TA complexes achieved a maximum resistant starch content of 26.08%. This study provides theoretical guidance for the development of SPI applications in starchy foods.