Fabrication and Characterization of Tunable High Internal Phase Emulsion Gels (HIPE-Gels) Formed by Natural Triterpenoid Saponin and Plant Soy Protein

High internal phase emulsion gels have attracted widespread attention. Here, two natural emulsifiers, plant soy protein isolate (SPI) and natural Quillaja saponin (QS), were investigated for the fabrication of high internal phase emulsion gels (HIPE-gels). It was found that tunable HIPE-gels were formed with different concentrations of SPI mixed with QS. A noncovalent hydrophobic interaction between SPI and QS served as an additive effect in reducing the surface tension and the droplet size of the resultant emulsions. Moreover, the flow and viscoelastic properties of the emulsion gels can be well adjusted by the specific interdroplet interactions and droplet size. Upon increasing SPI, the interdroplet stacking interaction among emulsion droplets promoted the formation of strong emulsion gels. Conversely, QS, as a structural modifier, progressively decreased the droplet size and gel strength. This is due to the fact that QS not only competitively squeezed out SPI from the oil-water interface but also enhanced the electrostatic repulsion of emulsion droplets. As a proof of concept, we demonstrate herein the successful development of high (10%) soy protein-based vegetarian mayonnaise. This finding would provide natural ingredients in the development of desired emulsions for the potential application of spreadable products, including saturated/trans-fat alternatives, high plant protein-based mayonnaise, and spreads.