Molecular mechanisms of bitterness and astringency in the oral cavity induced by soyasaponin

The interaction mechanism between soyasaponin (Ssa) and bitter receptors/mucin, as well as the saliva interface behavior of Ssa, were investigated to explore the presentation mechanism of Ssa bitterness and astringency (BA). Strong bitterness arising from high Ssa concentrations (0.5–1.5 mg/mL) had a masking effect on astringency. At Ssa concentrations of 1.0–1.5 mg/mL, Ssa micelles altered the structure of mucin, exposing its internal tryptophan to a more polar environment. At Ssa concentrations of 0.05–1.50 mg/mL, its reaction with mucin increased the aggregation of particles in artificial saliva, which reduced the frictional lubricating properties of oral saliva. Ssa-mucin interactions affected the salivary interfacial adsorption layer, and their complexes synergistically reduced the interfacial tension. Ssa monomers and soyasapogenols bind to bitter receptors/mucin via hydrogen bonding and hydrophobic interactions. Class A Ssa binds more strongly than class B Ssa, and thus likely presents a higher BA. In conclusion, Ssa interacts with bitter receptors/mucin causing conformational changes and aggregation of salivary mucin, resulting in diminished frictional lubricating properties of oral saliva. This, in turn, affects taste perception and gustatory transmission. •The difference in BA perception wasn’t obvious when Ssa was higher than 0.5 mg/mL.•Ssa-mucin complexes reduced interfacial tension and facilitated the release of BA.•Class A Ssa has a stronger BA than Class B Ssa.