In the present study, a water-in-oil-in-water (W/O/W) multiple emulsion was prepared with soyasaponin as an ingredient of the inner water phase (W₁), soybean protein as an ingredient of the outer water phase (W₂), and corn oil as the oil phase (O) via a two-step emulsification method. The effects of three different types of soybean protein: soybean protein isolate (SPI), 7S and 11S proteins on the overall stability, particle size characteristics, potential characteristics, microstructure, rheological properties, interfacial tension and long-term stability of the emulsion were investigated. Results indicated that the turbiscan stability index (TSI) value of the emulsion showed an upward trend over time and the particle size was concentrated around 6 μm. The absolute potential of the SPI-stabilized emulsion was the highest (-30.2 mV). The system exhibited pseudo-plastic shear thinning behavior, and had the highest viscosity (0.029 Pa·s). After 15 days of storage, all emulsions showed a creaming phenomenon, and the TSI of the SPI-stabilized emulsion was the smallest (21.51). The stability of the 1% SPI-stability emulsion was better than that of the emulsion stabilized with 1% 11S or 7S.

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.