Tailoring 3D-printed soy protein gels for dysphagia diets: Influence of xanthan gum's substituents and underlying mechanism.

The development of safe dysphagia diets demands precise control over the rheological and oral processing properties of food matrices. In this study, the effects of xanthan gum (XG) side-chain substituents (pyruvate and acetyl groups) on the interaction with soy protein isolate (SPI) and the functional properties of SPI-XG composite gels were systematically investigated. Rheological characterization confirmed that all SPI-XG composite gels displayed typical shear-thinning behavior, and XG incorporation significantly improved the printability of SPI gels by reducing viscosity and yield stress. At a shear rate of 1 s-1, viscosity decreased from 549.75 Pa·s to 347.37 Pa·s with decreasing pyruvate content, while yield stress decreased from 505.11 Pa to 375.40 Pa. Texture analysis showed that gel hardness decreased from 702.68 g to 489.32 g with reduced pyruvate substitution, whereas deacetylation increased hardness from 499.75 g to 593.13 g and gel strength from 74.75 g to 91.50 g. Low-field NMR results indicated that deacetylation reduced water mobility and promoted a more compact gel network. All SPI-XG gels satisfied the IDDSI Level 4 requirements for dysphagia diets. Tribological and electromyography analyses further demonstrated that XG incorporation reduced chewing resistance and muscle activity during mastication. Molecular interaction studies revealed that hydrogen bonding and van der Waals forces dominated SPI-XG associations, while pyruvate and acetyl groups modulated charge distribution and molecular packing. These findings clarify the structure-function relationship of XG substituents in SPI-based gels and provide guidance for designing 3D-printed texture-modified foods for dysphagia management.