Enhanced antioxidant and antiproliferative activities of Cymbopogon citratus (DC.) Stapf essential oils in microemulsion

Cymbopogon citratus essential oils (C.EO) have important applications in food and pharmaceutical industries. However, the studies on microemulsions of C.EO (M-EO) are very limited though M-EO from other plants have been extensively studied. In this study, C.EO were first extracted by hydrodistillation and characterized by gas chromatography–mass spectrometry analysis with the identification of citronellal (35.7%), citronellol (12.5%), and geraniol (16.6%) being the major oil compounds. Furthermore, M-EO were prepared using Tween 80 as a surfactant and ethanol as a cosurfactant, and the pseudo-ternary phase diagrams were depicted at different surfactant/cosurfactant (Km) and surfactant + cosurfactant/essential oil (Smix) ratios. The M-EO structure changes were investigated and elaborated through the determination of electrical conductivity and viscosity of the system prepared at a Km of 2:1 and an Smix of 8:2. M-EO was relatively stable after 90 days at an ambient temperature of 25 °C. Extracellular antioxidant activities of M-EO were improved by approximately 47% assessed by oxygen radical absorbance capacity assay and by 184% by peroxyl radical scavenging capacity assay compared to the direct use of C.EO. The cellular antioxidant activity of M-EO against liver cancer HepG2 cells was 151.1 ± 15.5 μmol quercetin equivalent/mg essential oils compared to negligible activity with C.EO. The EC50 of the antiproliferative activity of M-EO against HepG2 cells was 26.75 ± 2.91 μg essential oils/g, much lower than that (174.22 ± 8.20 μg essential oils/g) of C.EO. In addition, M-EO had little cytotoxicity against human normal cells, L02. The results obtained from this study indicate that microemulsions are very good systems for applications of C.EO in functional food and pharmaceutical industries.