Abstract: Recently, plant essential oil is increasingly applied as a bioactive component in the food industry. Lavender essential oil has multiple bioactivities such as sedative, hypnotic and antioxidant effects. However, poor hydrophobic properties limit its application in food products. In the present study, lavender essential oil microemulsion systems were constructed to evaluate their phase behavior and to investigate the influence of microstructure transformation on their free radical scavenging activity. According to the ternary phase diagram, dipropylene glycol acted as a co-surfactant to expand the single-phase area of microemulsions to 71.4%. Based on the results of dye diffusion and conductivity measurement, the dispersion phase was gradually inverted from a W/O stage (0%–30% water content) to a bicontinuous stage (40%–50% water content), and finally an O/W stage (60%–90% water content) along the dilution line. The viscosity peaked at the bicontinuous stage. This study found that the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging capacity was increased with the increase of water content. In addition, 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical scavenging capacity was reduced at the W/O and bicontinuous stages, followed by an increase at the O/W stage, peaking at a 70% water content. In conclusion, the systems can effectively improve the solubility of lavender essential oil, and there is a close association of their physical characteristics and antioxidant effect with microstructure transition.

Key words: lavender essential oil, microemulsion, phase behavior, microstructure transformation, free radical scavenging capacity