Regulating the structural, physicochemical, and digestive properties of sweet potato starch by complexation with...

This study investigated the effects of punicalagin on the physicochemical, structural, and digestive properties of sweet potato starch (SPS). Additionally, the inhibitory effect of punicalagin on amylase activities and the underlying mechanisms were examined. Results showed that punicalagin was bound to the SPS through hydrogen bonding and esterification, although the complexes retained an A-type crystal structure. The short-range ordered structure (R_1047/1017: 0.40-0.73) and long-range ordered structure (relative crystallinity: 1.53%-2.38%) of SPS were enhanced upon the addition of punicalagin. The SPS-punicalagin complexes exhibited smoother and more compact microstructures. Moreover, the punicalagin increased the solubility, transparency, gelatinization temperatures (onset, peak, and completion) of SPS and reduced the swelling power and gelatinization enthalpy. The SPS-punicalagin pastes exhibited pseudoplastic and shear-thinning behavior with altered storage modulus and loss modulus. Punicalagin increased the content of resistant starch, resulting in the reduction of the glycemic index (55.64-41.17). The hydrolysis resistance of punicalagin-SPS complexes was primarily attributable to punicalagin, which inhibited α-amylase and α-glucosidase by binding to their active sites, showing a stronger interaction observed for α-amylase. These findings indicated that punicalagin reduced the digestibility of SPS by changing the multi-scale structure of starch and suppressing amylase activity. This study provides valuable information for the development of health-oriented starch-based foods utilizing punicalagin.