From Synthesis Optimization to Chelation Mechanism: A Rice Protein Peptide–Calcium Complex Enhances Intestinal Calcium Absorption and Bone Formation via the TRPV6-Calbindin9k Axis

Rice protein peptides, abundant byproducts of rice processing, represent a sustainable source for developing novel nutritional delivery systems. To address the low bioavailability of traditional calcium supplements, this study aimed to fabricate a high-performance calcium-chelating complex (RPP-Ca) and elucidate its functional mechanism. The synthesis process was systematically optimized, yielding a maximum calcium-binding capacity of 93.98 ± 1.99 mg/g under optimal conditions (pH 10, 70 °C, 50 min reaction time, peptide-to-calcium mass ratio of 2:1). Physicochemical characterization utilizing scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) confirmed successful chelation, revealing significant microstructural reorganization and enhanced thermal stability compared to native peptides. Functional validation via in vitro Caco-2 cell models and in vivo calcium-deficient mouse models demonstrated that RPP-Ca significantly promotes intestinal calcium absorption and osteogenesis. Mechanistically, these effects were mediated through the activation of the TRPV6-Calbindin9k signaling axis. These findings underscore the potential of industrial rice protein peptides as an effective and bioavailable calcium fortification ingredient, providing a theoretical basis for the high-value utilization of rice byproducts in functional foods.