Externally triggered color and texture modulation in synergistic soy protein-hydrocolloid stabilized high internal...

Four-dimensional (4D) food printing has recently attracted attention as a means to fabricate stimuli-responsive foods capable of dynamic color and texture changes. However, most existing 4D systems rely on internal pH modulators or heat activation, resulting in slow ion diffusion, uneven color propagation, and weakened gel networks. To address these limitations, high internal phase Pickering emulsions (HIPEs) stabilized by soy protein isolate (SPI) and hydrocolloids, including Arabic gum (AG), xanthan gum (XG), and iota-carrageenan (IC), where developed as model systems to investigate protein-polysaccharide interactions and their effects on the structural and rheological properties of printable emulsions. Structural and molecular analyses, including via droplet size distribution, confocal microscopy, FT-IR, and molecular interaction assay, revealed that hydrocolloid incorporation, particularly 5 % XG, yielded the most stable emulsion with the smallest droplets and the highest post-shearing recovery rate, attributed to enhance hydrogen bonding and denser interfacial networks. Rheological analysis demonstrated shear-thinning, viscoelastic, and self-recovering behaviors, supporting accurate extrusion and structural fidelity. For 4D application, external pH modulation was applied by spraying pH-adjusting solution onto curcumin-loaded HIPEs constructs, inducing controllable color and texture transformation without thermal activation. Both XG- and IC-stabilized formulations exhibited high print precision, curcumin encapsulation efficiencies exceeding 94 %, and excellent retention. Overall, this study established an externally triggered 4D food printing platform capable of controllable color and texture changes, offering a practical route toward designing responsive and functionally stable food architectures.