Research on Physicochemical Properties and In Vitro Digestive Characteristics of High-Amylose Corn Starch–Ultrasound-Treated Waxy Rice Flour Blends

This study aimed to investigate the effect of high-amylose corn starch (HACS) addition on the physicochemical properties and in vitro digestibility of an ultrasound-treated waxy rice flour (UWRF)–HACS blend system. As the proportion of HACS increased, the amylose content in the blends significantly increased (p < 0.05), while their water solubility index (WSI) and swelling power (SP) significantly decreased (p < 0.05). Additionally, the average particle size of the blends increased, and the surface of starch granules became smoother. Compared to UWRF, the blends did not generate new functional groups, but increased the starch’s relative crystallinity and short-range ordered structure. Rheological results indicated that the HACS-UWRF blends were mainly elastic and exhibited a typical weak gel system. In vitro digestibility results showed that the addition of HACS significantly increased the resistant starch (RS) content in the rice cakes (p < 0.05), while substantially reducing the hydrolysis index (HI) and estimated glycemic index (eGI) (p < 0.05). This study revealed the processing characteristics and gelatinization behavior changes in the HACS-UWRF blends. It provides a theoretical basis for the development of specialized flour for slow-glycemic rice cakes.