Stabilization of orange oil-in-water emulsions: A new role for ester gum as an Ostwald ripening inhibitor

Orange oil-in-water emulsions (5% oil) stabilized by modified starch (2-10%) were prepared using high pressure homogenization. The initial droplet diameter decreased with increasing modified starch concentration, but all emulsions exhibited appreciable droplet growth during storage (15 days). The impact of adding a lipophilic weighting agent (ester gum) to the oil phase prior to homogenization was examined. Droplet growth could be inhibited by ensuring that the oil phase contained >9% ester gum, which was attributed to its ability to inhibit Ostwald ripening through an entropy of mixing effect. There was little effect of ionic strength (0-500 mM NaCl) or thermal treatment (30-90°C) on the stability of modified-starch stabilized emulsions containing orange oil and ester gum. This manuscript demonstrates that the primary role of ester gum (usually considered a weighting agent) in improving the stability of orange oil emulsions is to retard Ostwald ripening, rather than to act simply as a weighting agent. It was also demonstrated that corn oil could be used to retard Ostwald ripening by a similar mechanism in orange oil emulsions.