Influence of environmental stresses on O/W emulsions stabilized by β-lactoglobulin-pectin and β-lactoglobulin-pectin-chitosan membranes produced by the electrostatic layer-by-layer deposition technique

This manuscript describes the influence of environmental stresses, such as pH, ionic strength, and heating, on the stability of multilayer emulsions formed from natural polyelectrolytes. A "primary" emulsion was prepared by homogenizing 10 wt% corn oil with 90 wt% aqueous beta-lactoglobulin solution (0.5 wt% Blg, pH 7). This emulsion was mixed with aqueous pectin solution (0.4 wt%, 59% DE, pH 7) to yield emulsions containing 5 wt% corn oil, 0.225 wt% Blg, and 0.2 wt% pectin. The pH of this emulsion was then adjusted to pH 4 where anionic pectin adsorbs to the cationic protein-coated droplet surfaces and forms a "secondary" emulsion. This emulsion was rehomogenized to disrupt any flocculated droplets and was then added to chitosan solution (0.5 wt%, 90% DD, pH 4) to produce "tertiary" emulsions containing 2.5 wt% corn oil, 0.1125 wt% Blg, 0.1 wt% pectin, and 0.15 wt% chitosan. The stability of primary, secondary, and tertiary emulsions to pH (3-7), NaCl (0-500 mM), and thermal treatment (30 min at 30-90 degrees C) was determined using particle size, C-potential, and microstructure analysis. Primary emulsions were unstable at all pH, salt concentrations, and thermal treatments. Secondary emulsions were stable to droplet aggregation and creaming at 30-90 degrees C, at <= 100 mM NaCl, and at pH 3-5, whereas tertiary emulsions were stable at 30-60 degrees C, at <= 100 mNl NaCl, and at pH 3-6. These findings provide a better understanding of the possible use of these biopolymers to engineer O/W emulsion systems with improved physical stability.