Structural and physicochemical properties of subcritical water-extracted soy hull polysaccharides: Relationship to salty taste of sodium

Abstract

The reduction of sodium intake without affecting saltiness perception is still a huge challenge. The acid method (pH 2.0, 85 °C, 90min) and subcritical water treatment (SW, pH 6.3–2.0, 120 °C, 30min) were used to prepare saltiness-enhanced polysaccharides from soy hull. Structural and physicochemical properties of soy hull polysaccharides (SHP) and their relationship to the salivary diffusion and mucosal retention of Na+ were analyzed. Compared to acid-extracted SHP (ASHP), SW-extracted SHP (SW6.3, SW5.0, and SW4.0) exhibited a higher saltiness-enhanced effect, accompanied by an accelerated diffusion of Na+ in the saliva and enhanced adhesive retention of Na+ on the porcine tongue. These phenomena may be attributed to different fractions extracted by two methods. ASHP mainly consists of pectic polysaccharides with a higher galacturonic acid content, while RG-I enriched pectic and hemicellulosic polysaccharides were speculated for SW6.3, SW5.0 and SW4.0, which exhibited highly branched conformation with higher Mw and lower charge. The SHP-induced disruption of the salivary mucin network probably accelerates the Na+ permeation and the adhesion of Na+ on the porcine tongue. SW3.0 and SW2.0 showed lower apparent viscosity and Mw due to excessive degradation of the backbone and side chain, weakening the diffusion and adhesion of Na+, and salt taste. These results would be useful to reveal the regulatory mechanism of polysaccharides on saltiness perception, which provided a technology to prepare a saltiness-enhanced ingredient from a by-product of soybean processing for low-sodium foods.