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

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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 β-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°C) was determined using particle size, ζ-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°C, at ≤100 mM NaCl, and at pH 3–5, whereas tertiary emulsions were stable at 30–60°C, at ≤100 mM 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.