GC/MS analysis and antimicrobial and antioxidant activities of essential oil of Eucalyptus radiata

BACKGROUND: The essential oil from Eucalyptus radiata leaves collected in Tunisia was extracted by steam distillation and analysed by gas chromatography/flame ionisation detection and gas chromatography/mass spectrometry. Its antioxidant and antiradical properties were evaluated by the 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) assays. The antimicrobial activity of the oil was examined in vitro against two plant-pathogenic bacteria (four strains each of Agrobacterium tumefaciens and Pseudomonas savastanoi pv. savastanoi) and two plant-pathogenic fungi (Fusarium solani and Rhizoctonia solani). RESULTS: Thirty-five compounds were identified and quantified in the essential oil, the major ones being 1,8-cineole (69.53%), α-pinene (11.94%) and trans-pinocarveol (4.81%). Medium antioxidant activity was found in the ABTS assay (IC₅₀ = 484.3 ± 17.3 mg L⁻¹), whereas no significant free radical-scavenging activity was detected in the DPPH assay (IC₅₀ > 10 000 mg L⁻¹). The antimicrobial assays showed that the oil exhibited a high level of activity against A. tumefaciens and R. solani, with minimum inhibitory concentrations ranging between 750 and 1000 μL L⁻¹. However, it was less efficient against P. savastanoi pv. savastanoi and F. solani. CONCLUSION: The results indicate that the essential oil of E. radiata, with a high content of terpenic compounds, exhibits significant antimicrobial activity against strains of A. tumefaciens and the fungus R. solani and may therefore be useful for their control.