Mucoadhesive and sodium transport properties of some animal (Casein and Gelatin) and plant (Lotus Seed) proteins as a strategy for saltiness enhancement.

Proteins possess advantageous mucoadhesive and mucopenetrative properties when in contact with the oral mucosa, which might be used to modulate saltiness perception. The present study investigated the mucoadhesive properties of lotus seed protein (LP), compared to some animal proteins known for their mucoadhesion ability [casein (CA) and gelatin (G)]. To optimize and maximize the protein binding to mucin and the oral mucosa, we tested the binding at different protein concentrations (2 % - 10 % w/v) and pH levels (1.2 to 6.8). Since the human oral environment is about 37°C, all experiments were conducted at this temperature. The ability of proteins to interact with mucin was studied through mucin adsorption assay, turbidity, and viscosity increase. The charge density was also determined to understand the origin of mucoadhesion. The diffusion of sodium ions through a mucin-protein layer was investigated using a simulated tongue, while protein/Na+ex vivo retention experiments were conducted with real porcine tongues. Saltiness perception was also tested in vivo by a taste panel using sodium-containing protein solutions. The three proteins exhibited enhanced mucoadhesion at lower protein concentrations, with acidic conditions maximizing this interaction (p < 0.05). Under acidic conditions, Na+ diffusion was significantly higher (p < 0.05) for CA and LP. Sensory evaluation showed that LP enhanced perceived saltiness the most (intensity score of 5.04), compared to 4.22 for CA and 3.98 for G (p < 0.05). These biopolymers may have potential applications as salt reduction strategies in liquid and semi solid foods.