Enhancing the formation and stability of emulsions using mixed natural emulsifiers: Hydrolyzed rice glutelin and quillaja saponin

Abstract

Emulsifiers can often be used in combination to improve their functional performance. In this study, we examined the potential of combining two natural emulsifiers, hydrolyzed rice glutelin (HRG) and quillaja saponin (QS), on the formation and stability of oil-in-water emulsions. In particular, we investigated the impact of total emulsifier level, QS-to-HRG ratio, pH, ionic strength, and temperature on the mean particle diameter (d3,2), ξ-potential, creaming stability, and microstructure of the emulsions. The size of the oil droplets produced by homogenization decreased as the QS-to-HRG ratio increased from 1:4 to 1:1, but remained constant after that. The ξ-potential and dimensions of the droplets coated by the mixed emulsifiers were reasonably similar to those coated by QS alone, suggesting that the adsorbed saponins dominated the interfacial properties in the mixed systems. We also determined the physical stability of emulsions prepared using HRG, QS, or 1:1 QS-HRG after exposure to pH changes (pH 3–7), salt addition (0–500 mM NaCl, pH 7) and thermal treatment (30–90 °C 30 min, 200 mM NaCl, pH 7). QS-emulsions were stable to aggregation and creaming over a wider pH range than the other emulsions. Conversely, the mixed emulsions had better stability to high salt levels and temperatures (pH 7), which was attributed to a thicker interfacial layer causing stronger steric repulsion. This research may increase the utilization of plant-based emulsifiers in food and beverage applications.