Ca2+-Crosslinked Alginate Network Attenuates Starch Digestibility and Postprandial Glycemic Response in Rice Starch Gels

Rice starch (RS) is widely consumed, but is usually rapidly digested, which may increase postprandial blood glucose levels. Therefore, regulating RS digestibility is important for development functional starch-based foods. In this study, sodium alginate (NaAlg) was incorporated into RS gels and subsequently crosslinked with Ca2+ to form a calcium alginate (CaAlg) network, and its effects on the physicochemical properties, digestion behavior, and physiological responses of RS gels were evaluated. Rheological measurement showed that the Ca2+-crosslinked alginate network increased the viscosity and viscoelastic moduli of RS gels. Low-field nuclear magnetic resonance analysis showed that the Ca2+-crosslinked alginate network reduced free water mobility. Structural characterization using Fourier-transform infrared spectroscopy, X-ray diffraction, and cold-field scanning electron microscopy shows that the Ca2+-crosslinked alginate network was associated with enhanced intermolecular interactions and a more continuous gel network, while all gelatinized samples exhibited predominantly amorphous structures. In vitro digestion experiments showed that the hydrolysis degree at 120 min decreased from 92.3% in RS to 85.6% in HCaAlg/RS. The rapidly digestible starch content significantly decreased from 72.4% to 68.4% (p < 0.05), while resistant starch significantly increased from 7.7% to 14.4% (p < 0.05). First-order kinetic fitting showed that C∞ significantly decreased from 93.0% to 86.0%, and k significantly decreased from 0.027 to 0.013 min−1 (p < 0.05). In vivo experiments showed that the Ca2+-crosslinked alginate/RS gels were associated with a lower postprandial glycemic response, with the incremental area under the curve significantly decreased from 747.2 to 591.7 mmol·min/L (p < 0.05), and the intestinal propulsion rate decreased from 89.6% to 75.3% (p < 0.05). These results suggest that Ca2+-crosslinked alginate network formation may modulate the structural properties, digestion behavior, and digestion-related physiological responses of RS gels, providing a basis for the development of starch-based functional foods with improved glycemic control.