Balancing structural reinforcement and aggregation: Calcium-mediated regulation of soy protein isolate-rice starch...

Understanding how divalent ions regulate macromolecular interactions and network assembly in protein-polysaccharide systems is essential for designing functional food materials. In this study, calcium-mediated structuring was employed to modulate structural, rheological, digestive properties of protein-starch composite gels based on resistant starch and soy protein isolate. Different calcium salts were associated with distinct structural organizations, ranging from network reinforcement to aggregation-dominated assembly, resulting in tunable viscoelastic behavior and functional performance. Calcium citrate and calcium carbonate were associated with reinforced and more continuous gel networks, which may involve enhanced Ca²⁺-mediated intermolecular interactions and more balanced electrostatic conditions. In contrast, calcium chloride and calcium gluconate were associated with aggregation-dominated structures, which may be associated with differences in pH modulation, calcium availability, anion-dependent hydration behavior, resulting in heterogeneous structures with reduced network connectivity. Consequently, calcium citrate- and calcium carbonate-treated gels exhibited superior viscoelasticity, mechanical strength, and shape retention after 3D printing, whereas calcium chloride- and calcium gluconate-treated gels formed heterogeneous structures that were more susceptible to extrusion-induced disruption. Most formulations satisfied requirements of IDDSI Level 4, demonstrating their potential as texture-modified foods for individuals with dysphagia. These structural differences were closely associated with variations in water distribution, mechanical properties, digestion behavior, leading to enhanced protein digestibility, restricted starch hydrolysis, and improved calcium bioaccessibility. This study demonstrates that calcium salt type is an effective strategy for tailoring structural and functional characteristics of protein-starch composite gels, and offers a practical strategy for developing calcium-fortified 3D printable foods with tailored texture, digestion characteristics, and nutritional functionality.