Interspecific variability of 1,8-cineole content, phenolics and bioactivity among nine Eucalyptus taxa growing under the sub-humid bioclimate stage

Background Eucalyptus essential oils and extracts are used since the ancient times in alternative medicine. The 1,8-cineole is the most significant constituent of Eucalyptus essential oil, while phenolic contents define the value of eucalyptus extracts. Based on the last considerations, interspecific variability of 1,8-cineole content, phenolics and antioxidant potentials among nine Eucalyptus taxa growing under the sub-humid bioclimate stage of Tunisia was investigated. Methods Essential oil profiling was assessed based on gas chromatography-mass spectrometry analysis. Total phenolic and flavonoid contents were assessed using Folin-Ciocalteau and aluminium chloride colorimetric methods, respectively. The antioxidant ability of Eucalyptus volatile metabolites and extracts was achieved based on two test systems namely DPPH and FRAP assays. Results Qualitative and quantitative variations in the composition of essential oils according to the studied taxon were shown. The total phenolic and flavonoid contents varied also significantly among the investigated samples. Based on the obtained results, the species Eucalyptus sideroxylon exhibits the highest 1,8-cineole content (76.24 ± 0.86), total phenolics and flavonoids contents (38.5 ± 1.4 mg GAE /g DW and 18.6 ± 0.3 mg RE /g DW, respectively). Moreover this species highlighted the highest free radical-scavenging ability and ferric reducing power for both essential oil and methanolic extracts. Chemometric multivariate analysis showed the classification of the nine studied taxa to three clusters. Conclusions The pattern of 1,8-cineole concentration, phenolic and flavonoid contents for the studied nine Eucalyptus species and hybrid showed E. sideroxylon species as the potential candidate for further improvement strategies regarding the production of eucalyptus essential oils and phenolics with high quality for pharmaceutical industry.