The purpose of this study was to evaluate the usefulness of a simple theoretical model at predicting the stability of emulsions containing lipid droplets and polyelectrolytes. The influence of droplet concentration, mean droplet diameter, droplet charge and polyelectrolyte concentration on the aggregation stability of the emulsions was examined. Emulsions stabilized by a globular protein (beta-lactoglobulin) were prepared with different oil droplet (0.5-10 wt %) and pectin (0-0.5 wt %) concentrations at pH 7 (where lipid droplets and pectin molecules were both anionic) and pH 3.5 (where lipid droplets were cationic and pectin molecules anionic). The particle charge, size, and creaming stability of the emulsions were then measured, and stability maps were constructed at pH 3.5 and 7. At pH 7, there was no evidence of pectin adsorption to droplet surfaces, and the emulsions were stable to bridging flocculation, but depletion flocculation occurred when the pectin concentration exceeded about 0.1 wt % (independent of droplet concentration). At pH 3.5, pectin adsorbed to the droplet surfaces, and the emulsions were unstable to bridging flocculation at intermediate pectin concentrations (dependent on droplet concentration) and unstable to depletion flocculation at high pectin concentrations. At certain droplet and pectin concentrations, stable emulsions could be formed consisting of protein-coated lipid droplets surrounded by a pectin layer. The information gained from this study would be useful for optimizing the production of emulsions stabilized by protein-polysaccharide interfacial complexes.

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