Variation in chemical profile of leaves essential oils from thirteen Tunisian Eucalyptus species and evaluation of their antioxidant and antibacterial properties.

• Chemical composition and bioactivities of Eucalyptus essential oils varied significantly between the thirteen species. • 1,8-cineole was the main compound in majority of tested oils. spathulenol was the major one in E. camaldulensis. • Eucalyptus essential oils exhibited a weak antioxidant activity, but a remarkable bacterial inhibition growth. • E. camaldulensis had the strongest bioactivities. The aromatic medicinal plant Eucalyptus and its essential oils have been used since antiquity in folk medicine. The interest in this genus has increased remarkably over the last decade mostly because of their various biological activities. This study aimed to determine the chemical composition of essential oils of thirteen Eucalyptus species leaves and their antioxidant and antibacterial activities. Obtained results showed that E. maidenii had the highest essential oil yield (6.16 ± 1.55 %). Chemical composition (by GC/MS) was highly affected by the species factor (P < 0.001), with the abundance of the major compound 1,8-cineole (82.64 % in E. microcarpa) in most Eucalyptus species. Essential oils exhibited a moderate antioxidant activity, but an interesting bacteriostatic effect against all tested bacteria. Eucalyptus camaldulensis had the strongest bioactivities despite its major compound was spathulenol with efficacy concentration of 50 % EC 50 = 2.96 ± 0.11 mg/mL for the reducing power assay and presented an important inhibition zone (25.33 ± 2.84) and lowest minimum inhibitory concentration (MIC = 0.93 mg/mL) against Serratia marcescens bacteria. This result demonstrated that biological activities could be explained by the synergistic effect between major and minor compounds. [ABSTRACT FROM AUTHOR]