Formation and stability of emulsions using a natural small molecule surfactant: Quillaja saponin (Q-Naturale®)

Abstract

Q-Naturale® is a natural food-grade surfactant isolated from the bark of the Quillaja saponaria Molina tree. The major surface active components of Q-Naturale® are believed to be saponin-based amphiphilic molecules. In this study, we compared the effectiveness of this natural surfactant for forming and stabilizing emulsions with a synthetic surfactant (Tween 80) that is widely used in the food industry. We examined the influence of homogenization pressure, number of passes, and emulsifier concentration on the particle size produced. Q-Naturale® was capable of forming relatively small droplets (d < 200 nm) at low surfactant-to-oil ratios (SOR < 0.1) using high pressure homogenization (microfluidization), but the droplets were not as small as those produced using Tween 80 under similar conditions (d < 150 nm). Q-Naturale®-coated droplets were stable to droplet coalescence over a range of pH values (2–8), salt concentrations (0–500 mM NaCl) and temperatures (20–90 °C). However, some droplet flocculation was observed under highly acidic (pH 2) and high ionic strength (≥400 mM NaCl) conditions, which was attributed to screening of electrostatic repulsion. Indeed, Q-Naturale®-coated droplets had a relatively high negative charged at neutral pH that decreased in magnitude with decreasing pH. These results indicate that Q-Naturale® is an effective natural surfactant that may be able to replace synthetic surfactants in food and beverage products.