Stabilization and Rheology of Concentrated Emulsions Using the Natural Emulsifiers Quillaja Saponins and Rhamnolipids

Concentrated emulsions are widely used in the cosmetic, personal-care, and food industries to reduce storage and transportation costs and to provide desirable characteristics. The current study aimed to produce concentrated emulsions (50 wt % oil) using two natural emulsifiers, quillaja saponins and rhamnolipids. The impacts of emulsifier concentrations on the particle sizes, rheological properties, and stabilities of concentrated emulsions were evaluated. Emulsion particle sizes were negatively correlated with the concentrations of both quillaja saponins and rhamnolipids, and rhamnolipids were more effective in producing smaller droplets. Both emulsifiers formed stable concentrated emulsions against a series of environmental stresses, including various temperatures (30–90 °C), salt concentrations (≤200 mM NaCl), and pHs (pH 5–8). The rheology tests suggested that concentrated emulsions stabilized by quillaja saponins or rhamnolipids presented shear-thinning behaviors and had relatively low consistency coefficients.