The effects of ethanol content and emulsifying agent concentration on the stability of vegetable oil‐ethanol emulsions

Abstract

AbstractIn vegetable oil‐ethanol emulsions ethanol is the polar phase and vegetable oil is the nonpolar phase. The primary advantage of vegetable oil‐ethanol emulsions over conventional water‐oil emulsions is that they enable the incorporation of water‐and oil‐insoluble or poorly soluble functional compounds and/or drugs into emulsions. A number of nonionic surfactants were used to select appropriate stabilizers for stable vegetable oil‐ethanol emulsions. We found decaglycerol mono‐oleate (MO750) to be the best stabilizer for ethanol‐in‐oil (E/O) emulsions. The effects of ethanol content and of emulsifying agent concentration on the stability of vegetable oil‐ethanol emulsions were examined with MO750. After emulsification, two turbid layers formed simultaneously when ethanol content exceeded 20 wt%. The top layers (oil‐in‐ethanol emulsions; O/E emulsions) were very unstable, whereas the stability of the bottom layers (E/O emulsions) depended on the ethanol content. The stability of E/O emulsions is closely related to the effective concentration of MO750 aggregates, which play an important role in the film thickness stability of interfacial films formed by surfactant aggregates. Instability of E/O emulsion at 5 wt% MO750 is probably due to the polydispersity (i.e., nonuniform size and shape) of MO750 aggregates at high MO750 concentration. E/O emulsions prepared with 0.1, 0.5, and 1 wt% MO750 were stable, suggesting that the interfacial films formed were effective in protecting the droplets against coalescence and Ostwald ripening.