Synergistic interfacial properties of soy protein–stevioside mixtures: Relationship to emulsion stability

The dynamic interfacial tension and dilatational rheology of soy protein isolate (SPI) and stevioside (STE) mixtures at the oil–water interface were investigated to study the underlying stabilization mechanism for emulsions. The physical properties and long-term stability of emulsions prepared by SPI–STE mixtures were also evaluated. With bulk concentration of SPI fixed at 0.5%, the interfacial dilational properties and emulsion characteristics were markedly affected by the presence of low STE concentration (0.1%), although the interface was still dominated by SPI. With increasing STE concentrations to intermediate level (0.25–1%), synergistic effects in interfacial tension decays and a plateau in the elasticity for mixed SPI–STE interfaces were clearly observed. The effects should be mainly attributed to the formation of SPI–STE complex, enhancing interfacial protein–protein and protein–STE interactions, thus resulting in the presence of a plateau in the elastic behavior. These interfacial properties were positively reflected in the emulsions prepared by SPI–STE mixtures. The emulsions exhibited a fine formation ability and long-term stability after 120 days, which was believed to be due to their better response to external deformations. At high STE content (2%), STE dominated the formation of interface mainly by the preferential adsorption of STE molecules, as evidenced by the results of interfacial properties and surface protein load of emulsions. These findings would provide a potential strategy for designing emulsified foods with long-term stability.