Characterization and Bioactivity of Essential Oils from Geijera parviflora (Rutaceae): A Native Bush Medicine from Australia

Abstract

Essential oil was hydrodistilled from the Australian Wilga, botanically named G. parviflora Lindl., (Rutaceae). Fresh and aged essential oils were characterized using GC-MS, quantified using GC-FID and screened for bacterial inhibition qualitatively using disc diffusion and quantitatively using micro-titer plate broth dilution. To identify components responsible for bacterial inhibition, TLC-bioautography was used. Free radical scavenging capacity was determined using diphenylpicrylhydrazyl in methanol, and solvent extracts of the leaves using light petroleum, acetone and water were screened for qualitative pharmacological properties, as well as extracts produced by smoking the leaves and channeling into a condenser. Results showed that all essential oils extracted here conform broadly in composition to a previous identified chemotype with α-pinene, camphene and sabinene as the main constituents. As the essential oils age, polymerization of peroxide intermediates produced epoxycaryophyllene in at least one of our samples. The fresh oil showed only a modest level of antibacterial activity, but this became pronounced as the oil aged in storage, which resulted from a chemical change in the oil during years of storage at 4°C. Bioautography revealed that the antimicrobial capacity of the fresh oil may be attributed to its less abundant constituents, mainly α-terpineol, terpinen-4-ol, spathulenol, 1,8-cineole and camphor. The solvent extracts of the leaves revealed the presence of saponins, triterpenoids and alkaloids. The last two of these were also present in the smoke extract.