Modulation of sodium retention, diffusion, and saltiness perception via the interaction of Haematococcus pluvialis...

Optimizing the diffusion and retention behavior of sodium in the oral cavity is crucial for enhancing the perception of salty taste in food. This study demonstrated that a mucin/Haematococcus pluvialis polysaccharide (HPP) mass ratio of 1:3 effectively improved the diffusion and retention profiles of sodium within the oral cavity. This behavior was notably modulated by the sodium chloride (NaCl) concentration in the environment. To begin with, the effects of 0.3% to 1.5% HPP were investigated on oral behavior in both ex vivo pig tongue and in vivo saliva models. A 0.9% HPP solution more strongly retained sodium on the surface of the tongue. Subsequently, we assessed Na⁺ diffusion behavior in the mucin/HPP layer under varying NaCl concentrations (0-200 mM) to explore how mucin-HPP interactions alter mucin structure. Our results showed that the addition of HPP caused phase separation in the mucin-HPP mixture, mostly due to electrostatic repulsion. However, hydrogen bonding and physical entanglement facilitated by polysaccharide structure further induced structural changes in the mucin layer. Moreover, the results of diffusion wave spectroscopy (DWS) experiments confirmed that HPP promoted the diffusion of Na⁺ in the mucin layer. Atomic force microscopy (AFM) and cryo-scanning electron microscopy (cryo-SEM) revealed that under 200 mM NaCl conditions, the mucin/HPP mixture formed a mesh structure characterized by large pores, entanglement, and even a thin layer structure, which facilitated the retention and diffusion of Na⁺ in the mucin layer. The results of biological layer interferometry (BLI) analysis further confirmed that HPP interacted with mucin in the presence of NaCl and that the affinity between the two was NaCl concentration and mucin/HPP ratio dependent. These findings enhance our understanding of the mechanism by which polysaccharides regulate salt perception, offering reference for the development of low-sodium food salt enhancers using byproducts from microalgae processing.