Effect of fine structure of xanthan on its interaction with mucin: Toward designing of dysphagia diets.

Food sensory perception is strongly influenced by interactions between food components and salivary molecules, particularly mucin. This study systematically investigated the molecular interactions between mucin and xanthan gum (XG), a key thickener in dysphagia diets, to provide a theoretical basis for XG-based formulation design. The pyruvate and acetyl groups on XG side chains were identified as major determinants of these interactions. Depyruvylated XG (DPXG) reduced system charge density and weakened electrostatic interactions, resulting in lower intermolecular association and viscoelasticity, while deacetylated XG (DAXG) exposed more hydroxyl groups, enhanced hydrogen bonding, and promoted stronger conformational rearrangement. Circular dichroism analysis showed that XG and its derivatives induced only slight structural rearrangement of mucin rather than significant β-sheet disruption, with DAXG producing the most pronounced structural perturbation. Intrinsic fluorescence revealed that both DPXG and DAXG reduced fluorescence intensity, particularly DAXG, indicating greater tryptophan exposure and stronger fluorescence quenching. Tribological tests indicated scale-dependent lubrication behavior, with native XG maintaining the best lubrication performance, whereas DAXG showed lower friction in macroscale measurements but higher local friction at the microscale. Structural and computational analyses suggested that these differences were associated with changes in hydrogen-bonding and interfacial organization, providing guidance for XG-based dysphagia diet design.