Interfacial interaction of small molecular emulsifiers tea saponin and monoglyceride: Relationship to the formation and stabilization of emulsion gels

Abstract The oil-water (O-W) interface interaction of 1 wt% tea saponin (TS) and different monoglyceride (MAG) concentrations (0%–5%) was studied and further explored its relationship with emulsion gel properties. A combination of several analytical techniques such as microscopy, rheology, and infrared spectroscopy was used for macro and micro characterization of samples, respectively. Low concentrations (1%–3%) of MAG with TS had synergistic effects on the emulsification, the interface was dominated by fibrillar network of TS assembly though the co-adsorption of TS with the appropriate MAG. A combination of interfacial interaction and viscosity enhancement endowed obtained emulsion gels with improved properties, such as overall lower droplet size, homogeneous appearance, and better response to external deformations. However, in the presence of high MAG concentrations (4%–5%), interfacial films were readily subjected to the MAG crystal piercing, and with a reduced strength finally owing to the increasing distance and weakened hydrogen bonding of TS molecules. Besides, the interface and the subsequent formation and property of systems would be dominated by MAG. Thus, emulsion gels exhibited weak gel strength and declined stability. Because the number of protruding MAG crystals as well as the protruding distance was enhanced when the MAG content increased, droplet surface was completely destroyed and a collapsed system were formed. It was revealed that TS/MAG mixtures displayed interesting MAG concentration-dependence interfacial behaviors, which were closely related to the formation and stabilization of emulsions/emulsion gels. These findings would provide valuable information for the stabilization of emulsion gels involved in natural saponins.