Essential Oil Composition, Antioxidant Activity and Leaf Micromorphology of Five Tunisian Eucalyptus Species

Antimicrobial, Herbicidal and pesticidal potential of Tunisian eucalyptus species: Chemoprofiling and biological evaluation

The Eucalyptus genus, characterized by its imposing stature and fragrant foliage, has been a source of fascination for humanity over the centuries. The focus of the present investigation was directed towards the essentials oils (EOs) of five Eucalyptus trees cultivated in Tunisia. The GC-MS analysis unveiled unique compositional profiles, a finding substantiated by both Hierarchical Clustering Analysis (HCA) and Principal Component Analysis (PCA) conducted on the leaves EOs. These analyses resulted in the formation of discrete HCA clades, delineating 23 significant components. Notably, the percentage of eucalyptol emerged as the pivotal factor demarcating the separation between three distinct groups. The statistical analysis revealed a dose-dependent relationship in both phytotoxicity evaluation and antibacterial activity. The EOs from Eucalyptus loxophleba and E. salubris exhibited the highest phytotoxicity, inhibiting radical elongation and germination of various seeds, especially Sinapis arvensis and Raphanus sativus. The antimicrobial assessment demonstrated significant inhibitory effects of the EOs on bacterial strains, with MIC values spanning from 14 to exceeding 50 mg/ml. The EOs also affected biofilm formation and cellular metabolism, displaying varied efficacy among different Eucalyptus species against some bacterial strains. The EOs exhibited selective inhibition against acetylcholinesterase (AChE), butyrylcholinesterase (BChE), α-amylase, and α-glucosidase. E. campaspe EO showed the highest AChE activity, while E. loxophleba and E. salubris EOs were most potent toward α-amylase. E. loxophleba EO demonstrated notable activity against α-glucosidase. Overall, these findings provide important data about the diverse biological activities of Eucalyptus EOs, suggesting potential applications in agriculture, medicine, and pharmacy.

Phytochemical study on the essential oils of Callitris glaucophylla Joy Thomps. & L.A.S. Johnson, and assessment of their antioxidant, anti-enzymatic and allelopathic effects

Callitris glaucophylla Joy Thomps. & L.A.S. Johnson is a coniferous forest species of the Cupressaceae family native to Australia. This species is rich in essential oils (EOs) but few studies about variability and biological activity of these EOs are available in the literature. The purpose of this study was to evaluate the variability of production of C. glaucophylla EOs in relation to the different plant parts (needles, cones and stems) and to investigate their antioxidant, anti-enzymatic and herbicidal properties. EOs were obtained by hydro distillation and analyzed by GC and GC-MS. The antioxidant potential of EOs was assessed by ABTS, FRAP and DPPH assays, their phytotoxic activities were evaluated against germination and shoots and radical growth of Sinapis arvensis, Trifolium campestre, Lepidium sativum and Lolium rigidum. The EOs were evaluated for their possible anti-enzymatic effects with spectrophotometric assay. EOs resulted rich in monoterpenes hydrocarbons (61.04-77.82 %) and oxygenated monoterpenes (19.52-25.26 %). The main compounds were α-pinene as major compound in all plant parts (36.99-59.84 %), 1,8-cineole (19.88 % in stems) and limonene (18.94 % in needles). Herbicidal assays showed that all EOs have remarkable and significant phytotoxicity towards germination, roots, and aerial parts growth of the tested plants, depending on the EO, the doses and tested species. The EOs showed significant free radical scavenging potential and resulted more active against cholinesterases than α-glucosidase and α-amylase. The data obtained constitute an important contribution in selecting and valorizing appropriate forestry tree biomass as sources of antioxidant and phytotoxic molecules for sustainable application in food preservation and weeds control. The activities against the tested enzymes confirmed a possible use of these EOs as natural pesticides.

Essential oil and its nanoemulsion of Eucalyptus cladocalyx: chemical characterization, antioxidant, anti-inflammatory and anticancer activities

Formulating a nanoemulsion (NE) of essential oil (EO) could enhance its efficiency while requiring lower concentrations. Eucalyptus cladocalyx F. Muell EO was rich in monoterpenes hydrocarbons. NE was prepared and the effect of surfactant (Tween 20, 40 and 80) and shearing time were investigated. The results showed that the best NE was formed using Tween 80 after 25 min of emulsification. Small droplet size (40 nm), low polydispersity index PDI (0.49), and stable zeta potential highlighted the excellent NE stability which was tested under storage conditions for 4 months. The results showed that the antioxidant and anticancer activities of NE were enhanced compared to free EO. Furthermore, NE and EO exhibited high anti-inflammatory effects by inhibiting nitric oxide (NO), Interleukin 6 (IL-6), and tumor necrosis factors alpha (TNF-α) production in liposaccharides (LPS)-induced RAW264.7 cells. In conclusion, a stable Eucalyptus cladocalyx-NE was produced, with improved biological activities.

Chemical Composition, Antibacterial Properties, and Anti-Enzymatic Effects of Eucalyptus Essential Oils Sourced from Tunisia

This study was conducted to examine the chemical composition of the essential oils (EOs) from six Tunisian Eucalyptus species and to evaluate their anti-enzymatic and antibiofilm activities. The EOs were obtained through hydro-distillation of dried leaves and subsequently analyzed using GC/MS. The main class of compounds was constituted by oxygenated monoterpenes, particularly prominent in E. brevifolia (75.7%), E. lehmannii (72.8%), and E. woollsiana (67%). Anti-enzymatic activities against cholinesterases, α-amylase, and α-glucosidase were evaluated using spectrophotometric methods. Notably, the E. brevifolia, E. extensa, E. leptophylla, E. patellaris, and E. woollsiana EOs displayed potent acetylcholinesterase (AChE) inhibition (IC50: 0.25-0.60 mg/mL), with E. lehmannii exhibiting lower activity (IC50: 1.2 mg/mL). E. leptophylla and E. brevifolia showed remarkable α-amylase inhibition (IC50: 0.88 mg/mL), while E. brevifolia and E. leptophylla significantly hindered α-glucosidase (IC50 < 30 mg/mL), distinguishing them from other EOs with limited effects. Additionally, the EOs were assessed for their anti-biofilm properties of Gram-positive (Staphylococcus aureus and Listeria monocytogenes) and Gram-negative (Acinetobacter baumannii, Pseudomonas aeruginosa and Escherichia coli) bacterial strains. The E. extensa EO demonstrated the main antibiofilm effect against E. coli and L. monocytogenes with an inhibition > 80% at 10 mg/mL. These findings could represent a basis for possible further use of Eucalyptus EOs in the treatment of human microbial infections and/or as a coadjutant in preventing and treating Alzheimer's disease and/or diabetes mellitus.