Improving emulsifying properties using mixed natural emulsifiers: Tea saponin and golden pompano protein

Abstract

Emulsion stability could be improved by combining two natural emulsifiers. In this research, we studied the potential of combining golden pompano protein (GPP) and tea saponin (TS) on the O/W emulsion properties. At first, we investigated the influence of TS addition on the fourier transform infrared spectroscopy, free sulfhydryl content and fluorescence spectrum of the GPP. With the increase of TS addition, the content of α-helix decreased and the content of β-sheet increased, the free sulfhydryl content was also increased. We also determined the interfacial tension of GPP, TS and GPP-TS mixture. TS had stronger ability to reduce the oil-water interfacial tension. And the viscoelasticity of GPP-TS emulsion increased with the addition of TS, which might be due to the thickening effect of emulsifiers. These results indicated that the interaction between GPP and TS molecules was enhanced, which further increased the adsorption rate of GPP at the oil/water interface, reduced the interfacial tension, and improved the emulsification properties of the GPP-TS mixture. Compared with GPP emulsion, the mixed interfacial layer of GPP-TS emulsions got thicker and the steric repulsion become stronger. In addition, emulsion morphology was also affected by pH condition. GPP-TS emulsion droplets carried a great amount of net surface charge at alkaline condition, resulting in stronger electrostatic repulsion force and the emulsion distributed more uniformly. Rheological properties measurement indicated that the increase of TS addition increased the emulsion viscosity, thereby improving the emulsion stability. Our research demonstrated that the addition of TS could improve the GPP functional properties, and the GPP-TS mixture could form a more stable emulsion. This study showed that food-grade binary surfactant mixtures can be used to form stable emulsions with properties being tunable by altering the mixing ratios between surfactants. This mixed system demonstrated great potential as functional protein ingredient to control emulsion-type meat products or design of protein-based emulsion delivery systems in the food industry.