Eucalyptus cinerea and E. nicholii by-Products as Source of Bioactive Compounds for Agricultural Applications

Biochemical, Antioxidant, and Antimicrobial Profiling of Essential Oils of Indian Origin for Culinary Applications

This study investigated the biochemical composition and tested the antioxidant and antimicrobial properties of four Indian-origin essential oils (EOs)-ginger, garlic, clove, and eucalyptus-to evaluate their potential for culinary applications. Gas chromatography-mass spectrometry (GC-MS) analysis was used to identify the chemical constituents of EOs. Antioxidant assays such as 2,2-diphenyl-1-picrylhydrazyl (DPPH) and ferric reducing antioxidant power (FRAP) and antimicrobial assays such as Agar well diffusion, minimum inhibitory concentration (MIC), and minimum bactericidal concentration (MBC) were carried out. In GC-MS analysis, α-zingiberene (28.01%), eugenol (70.12%), 1,8-cineole (52.95%), and allyl polysulfides and terpenes were the most dominant compounds in ginger, clove, eucalyptus, and garlic EOs, respectively, which are responsible for their antioxidant and antimicrobial properties. Based on the antioxidant assays, clove EO exhibited the strongest antioxidant activities in both DPPH (70.84 ± 3.95%) and FRAP (142.29 ± 1.05 μ mol Fe (II) g-1) even at 5% level, suggesting its potential to inhibit lipid peroxidation, a process linked to oxidative stress in food. The antimicrobial study demonstrated the potential of EOs against foodborne pathogens, particularly against methicillin-resistant S. aureus (MRSA), which reveals their potential against multidrug-resistant bacteria. Among them, clove EO demonstrated the most potent antimicrobial activity against both Gram-negative and Gram-positive bacteria, with notable activity against MRSA with an inhibition zone of 41.33 ± 0.57 mm. This strong antimicrobial activity of clove EO was directly correlated with its total phenolic content (375.91 ± 14.21 mg phenols 100 g-1 at 5% level). The results indicated that clove EO stands out for its strong antioxidant and antimicrobial properties, particularly against multidrug-resistant pathogens like MRSA. These findings suggest clove EO could be a promising natural alternative to synthetic preservatives and antibiotics in culinary applications, helping to preserve food and combat resistant bacteria.

Comparing diverse extraction methodologies to infer the performance of 1,8-cineole extraction from Eucalyptus cinerea: process optimization, kinetics, and interaction mechanisms

Eucalyptus oil is highly valued for its anti-inflammatory, antiviral, and antibacterial qualities. Research has shown that it is a powerful combatant against cancer cells, making it an extremely interesting area of research. For the first time, the present study proposes to extract 1,8-cineole from Eucalyptus cinerea leaves using different extraction methodologies, namely, hydro-distillation (HD), Soxhlet (SE), ultrasonication (UE), and microwave (ME) extraction techniques. In conventional extraction, HD yielded a maximum of 72.85% 1,8-cineole using a minimum solid-solvent ratio of 1 : 10 g mL-1 within 3 h compared to SE. The first-order kinetic equation was applied in the HD experimental dataset to understand the extraction mechanism. In modern extraction technology, ME achieved the highest yield of 1,8-cineole (95.62%) at the optimal solid-solvent ratio of 2 g mL-1, extraction time of 4.5 min, and irradiation power of 640 W using the response surface methodology (RSM). Furthermore, the kinetic analysis of UE was investigated using three different empirical models. The chemical components of the essential oil extracted using each extraction method were identified as oxygenated monoterpenes, sesquiterpenes, and oxygenated sesquiterpenes using gas chromatography. Following extraction using various techniques, the morphology of spent leaves lost its distinct texture, their oil glands were entirely distorted, and their vascular bundles could still be identified. It was observed that the hydrogen bond interaction between the solvent molecule and 1,8-cineole-like value-added components played a role in the extraction. Among the investigated techniques, the solvent-free ME method is the most environmentally acceptable method and could effectively extract essential oil from E. cinerea leaves.

Artemisia arborescens (Vaill.) L.: Micromorphology, Essential Oil Composition, and Its Potential as an Alternative Biocontrol Product

Artemisia arborescens is a Mediterranean evergreen shrub, with silver grey-green tomentose leaves and a strong scent. It has various ethnopharmacological uses and its secondary metabolites have demonstrated antimicrobial, antiviral, pharmaceutical, phytotoxic, and insecticidal activities. Different extracts obtained from aerial parts of this species are known for their allelopathic effect, but similar studies on its essential oil (EO) are lacking. Therefore, we carried out a pharmacognostic study, obtaining the characterization of the secretory structures and the EO produced. Trans-thujone and camphor are the main components, followed by aromadendrene, camphene, and 8-cedren-13-ol. EO phytotoxic activity was tested on weed plants (Lolium multiflorum Lam. and Sinapis arvensis L.) and crops (Raphanus sativus L. and Cucumis sativus L.), showing inhibition on both germination and radical growth of the two weeds tested. The effects of the EO against the bacterial plant pathogens Xanthomonas campestris pv. campestris (Gram-) and Pseudomonas syringae pv. tomato (Gram+) was also assayed. The minimum inhibitory concentration (MIC) was observed when it was used undiluted [100% v/v], and growth inhibition when diluted at different doses. The antimicrobial activity was also confirmed by the cellular material release and biofilm formation assays. The overall data show that A. arborescens EO can find application as a potential alternative biocontrol product against weeds and plant pathogens. This goal is particularly important from the perspective of replacing synthetic pesticides with natural products, which safeguard both the environment and the health of consumers.

Plant Essential Oils as Biopesticides: Applications, Mechanisms, Innovations, and Constraints

The advent of the "Green Revolution" was a great success in significantly increasing crop productivity. However, it involved high ecological costs in terms of excessive use of synthetic agrochemicals, raising concerns about agricultural sustainability. Indiscriminate use of synthetic pesticides resulted in environmental degradation, the development of pest resistance, and possible dangers to a variety of nontarget species (including plants, animals, and humans). Thus, a sustainable approach necessitates the exploration of viable ecofriendly alternatives. Plant-based biopesticides are attracting considerable attention in this context due to their target specificity, ecofriendliness, biodegradability, and safety for humans and other life forms. Among all the relevant biopesticides, plant essential oils (PEOs) or their active components are being widely explored against weeds, pests, and microorganisms. This review aims to collate the information related to the expansion and advancement in research and technology on the applications of PEOs as biopesticides. An insight into the mechanism of action of PEO-based bioherbicides, bioinsecticides, and biofungicides is also provided. With the aid of bibliometric analysis, it was found that ~75% of the documents on PEOs having biopesticidal potential were published in the last five years, with an annual growth rate of 20.51% and a citation per document of 20.91. Research on the biopesticidal properties of PEOs is receiving adequate attention from European (Italy and Spain), Asian (China, India, Iran, and Saudi Arabia), and American (Argentina, Brazil, and the United States of America) nations. Despite the increasing biopesticidal applications of PEOs and their widespread acceptance by governments, they face many challenges due to their inherent nature (lipophilicity and high volatility), production costs, and manufacturing constraints. To overcome these limitations, the incorporation of emerging innovations like the nanoencapsulation of PEOs, bioinformatics, and RNA-Seq in biopesticide development has been proposed. With these novel technological interventions, PEO-based biopesticides have the potential to be used for sustainable pest management in the future.

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

Eucalyptus species have been widely employed in the projects of reforestation in Tunisia. Although their ecological functions are controversial, these plants are indeed important to counteract soil erosion, and represent a fast-growing source of fuelwood and charcoal wood. In the present study, we considered five Eucalyptus species, namely Eucalyptus alba, E. eugenioides, E. fasciculosa, E. robusta, and E. stoatei cultivated in the Tunisian Arboreta. The aim was to carry out the micromorphological and anatomical characterization of the leaves, the extraction and phytochemical profile of the essential oils (EOs), and the evaluation of their biological properties. Four of the EOs showed the prevalence of eucalyptol (1,8-cineole) varying from 64.4 to 95.9%, whereas a-pinene predominated in E. alba EO (54.1%). These EOs showed in vitro antioxidant activity, and reduced the oxidative cellular stress as shown by their activity on reactive oxygen species (ROS) production, and modulation of the expression of antioxidant enzymes, such as glutamate-cysteine ligase (GCL) and heme oxygenase-1 (Hmox-1). Moreover, the EOs inhibited the production of nitric oxide (NO), showing anti-inflammatory activity. The data collected suggest that these EOs may be considered a promising therapeutic strategy for inflammation-based diseases and may represent an additional value for the economy of Tunisia.

Essential Oils and Biological Activities of Eucalyptus falcata, E. sideroxylon and E. citriodora Growing in Tunisia

Many plants are able to synthesize essential oils (EOs), which play key roles in defense against weeds, fungi and pests. This study aims to analyze the chemical composition and to highlight the antioxidant, antimicrobial and phytotoxic properties of the EOs from Eucalyptus falcata, E. sideroxylon and E. citriodora growing in Tunisia. EOs were analyzed by gas chromatography coupled to mass spectrometry (GC/MS) and their antioxidant properties were determined by total antioxidant capacity (TAC), DPPH and ABTS assays. The phytotoxic potential was assessed against weeds (Sinapis arvensis, Phalaris canariensis) and durum wheat crop (Triticum durum) and compared to chemical herbicide glyphosate. The antifungal activity was investigated in vitro against eight target fungal strains. All EOs displayed a specific richness in oxygenated monoterpenes (51.3-90%) and oxygenated sesquiterpenes (4.8-29.4%), and 1,8-cineole, citronellal, citronellol, trans-pinocarveol, globulol, spathulenol and citronellyl acetate were the main constituents. Eucalyptus EOs exhibited remarkable antioxidant activity and E. citriodora oil exhibited significant activity when compared with E. falcata and E. sideroxylon EOs. The phytotoxic potential of the tested oils had different efficacy on seed germination and the growth of seedlings and varied among tested herbs and their chemical composition variability. Their effectiveness was better than that of glyphosate. At the post-emergence stage, symptoms of chlorosis and necrosis were observed. Furthermore, a decrease in chlorophyll and relative water content, electrolyte leakage and high levels of MDA and proline were indicators of the oxidative effects of EOs and their effectiveness as bioherbicides. Moreover, all the EOs exhibited moderate fungitoxic properties against all the tested fungal strains. Therefore, according to the obtained results, Eucalyptus EOs could have potential application as natural pesticides.