Evaluation of phase behavior, microstructure transition and antiradical activity of lavender essential oil-based microemulsions

Lavender essential oil (LO) is widely used as a bioactive component in cosmetics. In this study, the pseudo ternary phase diagrams of microemulsions composed of oil phase (LO: short-chain alcohol = 1:1, w/w), nonionic surfactant (Tween 80) and water were constructed to evaluate the impact of cosurfactant type on the dilutability of microemulsion systems. The solubilization of LO was improved in the presence of 1,3-butylene glycol. For this reason, microstructural inversion of a water titration line D82 was investigated by dye diffusion, conductivity, viscosity and DSC. Microemulsions transition from W/O to bicontinuous occured at 20% water content, and then to O/W structure at 50% water content. In the bicontinuous phase, the viscosity reduced rapidly by the rise of temperature. The structure transition affected the free radical scavenging activity. The DPPH radical scavenging activity increased continuously with water content from 10% to 90%, indicating that increasing free water may accelerate the interaction between LO and DPPH radicals. The ABTS radical scavenging activity of W/O and bicontinuous formulations was concentration-dependent while increased again and peaked at 70% water content in O/W regions. The microemulsion techniques could be applied as potential delivery systems to improve the application of poorly water-soluble essential oils. [GRAPHICS] .