Abstract
In this study, essential oil and various extracts (hexane, petroleum ether, acetone, ethanol, methanol and water) of Eucalyptus gilii were screened for their chemical composition, antimicrobial and antioxidant activities. The essential oil chemical composition was analyzed by gas chromatography-mass spectrometry (GC-MS) and gas chromatography-flame ionization detection (GC-FID), respectively. Thirty four compounds were identified, corresponding to 99.5% of the total essential oil. Tannins [104.9–251.3 g catechin equivalent (CE)/Kg dry mass], flavonoids [3.3–34.3 g quercetin equivalent (QE)/Kg dry mass], phenolics [4.7–216.6 g gallic acid equivalent (GAE)/Kg dry mass] and anthocyannins [1.2–45.3 mg cyanidin-3-glucoside equivalent (C3GE)/Kg dry mass] of various extracts were investigated. Free radical scavenging capacity of all samples was determinedt. In the 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay, the IC50 of essential oil was 163.5 ± 10.7 mg/L and in the 2,2'-azinobis-3-ethylbenzothiazoline-6-sulphonate (ABTS) assay, it was 94.7 ± 7.1 mg/L. Among the various extracts, the water extract showed the best result (IC50 = 11.4 ± 0.6 mg/L) in the DPPH assay which was comparable to vitamin C (IC50 = 4.4 ± 0.2 mg/L). The antimicrobial activities were evaluated against different bacterial and fungal strains. Gram positive bacteria were found to be more sensitive to the essential oil and extracts than Gram negative ones. Anthocyanins seem to have a major effect on the growth of Bacillus subtilis (R2 = 0.79). A significant antifungal activity was observed against the yeast and fungi. Correlations between chemical composition and antioxidant activities were studied and R2 values were about 0.96 for the effect of phenolics on the DPPH assay.
Highlights
In all regions of the World, history shows that medicinal plants have always held an important place
The antimicrobial activity of E. gillii essential oil was evaluated by the determination of the Minimum Inhibitory Concentration (Table 4), which is the first concentration of added essential oil with which we do not notice visible microbial growth
Concerning Gram negative bacteria, Salmonella enterica was the most sensitive, with a 17 mm inhibition zone obtained with the petroleum ether extract, followed by K. pneumoniae, P. aeruginosa and E. coli which were more resistant against the various extracts
Summary
In all regions of the World, history shows that medicinal plants have always held an important place. Essential oils have broad spectrum of activity against different bacterial and fungal strains [3] Their antimicrobial activity is mainly based on their chemical composition, in particular the nature of their main volatile components [3,4,5,6]. These medicinal plants are distributed worldwide, for example in Tunisia, where the climatic conditions are favorable for wild, cultivated and introduced plants. Eucalyptus is mainly cultivated for its timber, pulp and essential oils that present medicinal properties and therapeutic uses.
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