Oil-in-water emulsion system stabilized by protein-coated nanoemulsion droplets

Nanoemulsion droplets (average size of about 150 nm) coated with micellar casein were used as an emulsifying agent to stabilize oil (n-hexadecane)-in-water emulsions. We found that these nanodroplets adsorbed at the oil-water interface and formed stable emulsions, with the size of the droplet-stabilized emulsions being dependent on the concentration of nanodroplets in the dispersions. Stable emulsions were still formed at low concentrations, even though the interface was not fully covered by the nanodroplets. The nanodroplets fully covered the interface at higher concentrations, resulting in a transition from a thick interfacial layer to a multilayer containing a network of assembled nanodroplets. Because of their soft and elastic nature, the adsorbed nanodroplets showed strong deformation at the oil-water interface. The morphology of the interfacial nanodroplets was dependent on their location inside the network interfacial layer. The adsorption and deformation of the droplets at the oil-water interface and the formation of network structures, as observed in the present study, provide new, useful fundamental knowledge with potential applications for microencapsulation and emulsion stabilization.