Chitosan Coating Improves Retention and Redispersibility of Freeze-Dried Flavor Oil Emulsions

Flavor oils are often encapsulated as emulsions by drying processes such as freeze-drying or spray-drying, using mainly macromolecular emulsifiers such as gums and proteins to stabilize the emulsions during drying. The objective of the present study was to examine whether a combination of a charged small-molecule emulsifier and an oppositely charged polysaccharide adsorbed to the emulsion droplet surface can substitute commonly used encapsulation materials for the drying of flavor oil emulsions. To this end, polysaccharide-coated flavor oil emulsions were prepared by high-pressure homogenization of mixtures consisting of a flavor oil (R-carvone), a negatively charged citric acid ester small-molecule emulsifier (citrem), and various concentrations of a positively charged polysaccharide (chitosan) in acetate buffer at pH 4.0. Nanoemulsions with average particle diameters of approximate to 100 nm in the absence and approximate to 230-250 nm in the presence of chitosan coating were obtained. These emulsions were subsequently freeze-dried with different concentrations of maltodextrin, which served as the main encapsulation material. It was demonstrated that coating the oil droplet surface with a small amount of chitosan resulted in remarkably improved retention levels and redispersibility properties of the freeze-dried carvone emulsions. Maltodextrin content also affected both retention and redispersibility. At optimal chitosan and maltodextrin concentrations approximate to 95% retention levels were obtained, and the average particle sizes of freeze-dried and redispersed emulsions were approximate to 270-300 nm, as compared to approximate to 230-250 nm before freeze-drying. The results demonstrate that charged small-molecule emulsifiers used in combination with oppositely charged polymers are viable alternatives to macromolecular emulsifiers for freeze-drying of flavor oil emulsions.