Saltiness Enhancement Modulated by Hydrophobic Mucoadhesion of Soy Hull Pectic-Like Polysaccharides within a Salivary Mucin Layer

Na⁺ saltiness perception strongly depends on its diffusion and retention within the salivary layer, processes modulated by mucoadhesive polysaccharides. However, the underlying saltiness-enhancing mechanism of soy hull polysaccharide (SHP) remains unclear due to its compositional and structural heterogeneity. SHP was separated into neutral (SHP-N, hemicellulose) and acidic (SHP-A, RG-I-enriched pectin) fractions. Salivary mucoadhesion of Na⁺ and SHP were investigated. Compared to SHP-N, negatively charged SHP-A exhibited a stronger saltiness-enhanced effect by accelerating Na⁺ diffusion and prolonging retention, which is not mainly attributed to viscosity changes. The electrostatic screening effect of Na⁺ promoted stable mucoadhesion of SHP-A on the mucin layer. Strong hydrophobic interaction as the dominant force is primarily mediated by protein domains within the rhamnogalacturonan I (RG-I) region of SHP-A. Strong SHP-mucin affinity may influence Na⁺ adsorption-desorption dynamics and accelerate its penetration. This work reveals key structural domains of polysaccharides responsible for saltiness enhancement and their mucoadhesive driving forces in salivary layer.