David N Leach

Southern Cross University, Лизмор, New South Wales, Australia

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Publications (105)104.21 Total impact

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    ABSTRACT: This study describes the antioxidant and insecticidal activities of essential oils (EOs) of Mentha suaveolens subsp. timija, Thymus satureioides, Achillea ageratum, Cotula cinerea and Salvia officinalis widely used in Morocco as flavorings, food additives and preservatives. Sixty seven components were identified accounting for more than 95.0 % of the total oils. M. suaveolens subsp. timija oil had as main components menthone and pulegone. A. ageratum oil was particularly rich in artemisyl acetate and yomogi alcohol. The essential oil of T. satureioides was characterized by high contents of carvacrol and borneol. C. cinerea oil contained trans-thujone and cis-verbenyl acetate as major constituents, whereas S. officinalis oil was characterized by trans-thujone and camphor. Antioxidant activities were examined by means of 2,2-diphenyl-1- picrylhydrazyl radical (DPPH), reducing power, β-carotene/linoleic acid bleaching and ABTS radical tests. In all assays, the highest antioxidant potency was observed in T. satureioides EO with IC50 values ranging from 0.15±0.36 μg mL-1 to 0.23±0.67 μg mL−1 across the four assays. The in vitro evaluation of the insecticidal activity showed that M. suaveolens subsp. timija EO present the highest insecticidal efficiency against adults of Tribolium castaneum with LD50 and LD90 values of 0.17 μL cm−2 and 0.26 μL cm−2, respectively, and LT50, LT90 values ranged from 44.19 h to 2.98 h and 98.14 h to 6.02 h, respectively. Our data support the possible use of T. satureioides oil as potential antioxidant agent, while M. suaveolens subsp. timija oil can be developed as a new natural bio-insecticide.
    Journal of Food Science and Technology -Mysore- 02/2014; · 2.02 Impact Factor
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    ABSTRACT: Hydro-distilled essential oils (EOs) from the aerial parts of wild and cultivated Salvia aucheri subsp. blancoana, an endemic and threatened medicinal species of Morocco, were analyzed by GC/MS and screened for their antioxidant and insecticidal activities. In total 23 compounds representing more than 98.7% of the total oils were identified. Camphor (26.6–57.3%), camphene (6.3–22.0%), α-pinene (4.1–20.6%) and (E)-caryophyllene (5.4–5.7%) were found as the main constituents of the two oils. The EOs of the wild and cultivated material differed significantly in both the percentage of the main components and their biological activity. Camphor was more dominant in wild Moroccan sage oil (57.3%) than in cultivated sage (26.6%), while camphene (22.0%) and α-pinene (20.6%) were more abundant in the cultivated material compared to 6.3% and 4.1% respectively in wild sage. Regarding the biological activity, cultivated Moroccan sage oil showed the highest antioxidant activity, while the wild plant EO was the most effective against adults of the red flour beetle Tribolium castaneum Herbst.
    Industrial Crops and Products 01/2014; 57:106–109. · 3.21 Impact Factor
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    ABSTRACT: Thymus leptobotrys and T. maroccanus are endemic Moroccan medicinal species that are intensively exploited from the wild because of their wide ranging therapeutic properties. In order to preserve these valuable medicinal plants from risk of extinction, the cultivation (with and without N, P, and K fertilizer) and its consequent effect on oil chemical composition and biological activities were studied. Carvacrol (64.1–78.1%) was found as the major constituent in oil samples, followed by p-cymene (4.7–12.4%) and γ-terpinene (3.2–7.9%). Cultivation without using N, P, and K fertilizer caused a slight decrease in carvacrol content against an increase of its main precursor p-cymene. However, application of N, P, and K fertilizer increased the carvacrol content of 3.9% for T. maroccanus and 9.4% for T. leptobotrys oils compared with unfertilized plants. Regarding the antioxidant activity, wild thyme oils showed the highest potency in all assays, while oils from cultivated plants fertilized with N, P, and K had greater activity than oils from plants not receiving fertilizer. Concerning the antimicrobial activity, oils from fertilized plants exhibited the highest inhibitory effect against most tested strains with MIC values ranged from 0.03 to 31.68 mg/mL. From this work, it can be concluded that cultivation could be a promising solution to ensure the sustainable utilization of these endemic and threatened medicinal thyme species.
    Industrial Crops and Products 01/2014; 62:113–118. · 3.21 Impact Factor
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    ABSTRACT: Mentha suaveolens subsp. timija is a strict Moroccan endemic species that is intensively exploited from the wild because of its wide ranging medicinal and culinary properties. This has resulted in the species becoming rare or threatened with risk of extinction in the wild. In order to ensure the conservation and sustainable utilization of this valuable medicinal and aromatic plant, its cultivation has been suggested as a promising solution. However, many uncontrolled factors can affect this cultivation including salinity. Thus, the present work aims to evaluate the effects of saline conditions simulated by different NaCl concentrations (0, 50, 100 and 150 mM) on growth (fresh and dry weights), mineral content, essential oil (EO) quantity and quality of M suaveolens subsp. timija. The experiment was conducted inside a shade house at the experimental garden at the Faculty of Sciences, Semlalia-Marrakech during the growing season (February–May) of the year 2010. The results showed that increasing NaCl levels to 150 mM reduced significantly the fresh and dry biomass production by 47.558% and 69.324%, respectively, in comparison to the control. Application of NaCl induced also an increase in Na+ content, while K+ content and K+/Na+ ratio decreased with increasing salt stress. The EO yield decreased by 38.9% and 50.6% at 100 and 150 mM NaCl, respectively, compared with the control (0.77 ± 0.14%). Pulegone, menthone and isomenthone were found to be the principal components of M suaveolens subsp. timija EO. The relative abundance of menthone in particular was affected by salt stress. Based on the present results, it can be concluded that mint timija is a salt sensitive crop and cannot be cultivated in salt-affected areas.
    Industrial Crops and Products. 01/2014; 59:80–84.
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    ABSTRACT: The essential oils (EOs) of Artemisia herba alba, Rutachalepensis and Satureja calamintha aerial parts were analysed by GC/MS and the EOs were tested for their toxicity against two flour beetles, Tribolium castaneum and Tribolium confusum. EO composition showed that the major compounds were pulegone, menthone and menthol for S. calamintha, camphor and β-thujone for A. herba alba and 2-undecanone for R. chalepensis. Contact bioassay showed that all EOs were toxic to adults of T. castaneum and T. confusum. Higher toxicity was found with the EOs from S. calamintha and R. chalepensis (LD50 of 0.09-0.13 μL/cm(2) and LD90 of 0.17-0.29 μL/cm(2)). In fumigant toxicity test, A. herba alba and S. calamintha EOs produced insecticidal activity with S. calamintha EO being more toxic with LD50 and LD90 values of 10.5 and 19.1 μL/L air, respectively, for T. confusum against 7.8 and 17.4 μL/L air, respectively, for T. castaneum.
    Natural Product Research 01/2014; · 1.03 Impact Factor
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    ABSTRACT: Thymus saturejoides is a perennial shrub widely distributed in the arid and semi arid parts of the Moroccan mountains. Essential oils (EOs) of this species are used extensively in food and pharmaceutical industries because of their wide biological and pharmacological properties. To our knowledge, no data are available on the antibacterial and antioxidant activities of T. saturejoides EOs in relation to the chemical variability of the species. Also, the potential synergistic interaction of EOs from this species as natural antimicrobial agent with conventional antibiotics against food-borne bacteria has not been investigated. Thus, the aim of the present study was to determine the volatile oil constituents of EOs from three wild Moroccan T. saturejoides populations collected from Northwest–Southeast of Morocco (June, 2011). Antioxidant activity and their antibacterial potency (singly and in combination with cefixime) against selected food-borne bacteria was then determined. Gas chromatography–mass spectrometry (GC–MS) analysis revealed 30 compounds, representing 98.6 to 99.5% of the total oils. The major constituents identified were carvacrol (45.3%), p-cymene (8.9%), linalool (8.4%), and borneol (7.5%) in oil from the Er-Rich population (arid site); carvacrol (26.5%), borneol (20.1%), camphene (8.0%), and γ-terpinene (5.6%) in oil from Ourika population (medium arid site) and carvacrol (25.3%), borneol (19.7%), camphene (7.6%), and p-cymene (6.6%) in oil from Taws population (less arid site). Essential oil obtained from Er-Rich population showed the highest antioxidant activity as measured by 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging ability, reductive potential, and β-carotene/linoleic acid assays with IC50 values of 44.54 ± 0.92 μg/mL, 22.90 ± 0.16 μg/mL and 19.17 ± 0.01 μg/mL, respectively. Antibacterial tests showed that the oils from this species had a high inhibitory activity against tested bacteria, with the exception of Pseudomonas aeruginosa. The most potent activity was observed with oil obtained from the Er-Rich population with minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values of 0.14 to 0.55 mg/mL and 0.28 to 0.55 mg/mL, respectively. Out of 21 combinations tested between EOs and cefixime, 67% showed total synergism, 19% had partial synergistic interaction and 14% showed no effect. Oil from the Er-Rich population exhibited the highest synergistic effect with antibiotic (FIC index values of 0.29 to 0.5). The synergy displayed by this combination of EO and cefixime may be of potential benefit for control of food-related bacteria, consequently permitting the use of lower doses of standard antibiotics.
    Industrial Crops and Products 01/2014; 61:338-344. · 3.21 Impact Factor
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    Dataset: SP08003
    Stewart W Wossa, Topul Rali, David N Leach
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    ABSTRACT: The chemical composition, antioxidant and antimicrobial activities of essential oils isolated by hydrodistillation from the aerial parts of wild endemic Moroccan Thymus maroccanus at different developmental stages (vegetative, flowering and post-flowering) were evaluated. The yield of essential oils (v/w%) based on dry weight at different stages were: vegetative (2.14%), flowering (leaves: 1.80%; flowers: 3.46%), and post-flowering (leaves: 0.98%; post-flowers: 2.46%). Analysis of the essential oils by GC/MS revealed the presence of 28 components represented mainly by monoterpenes, both oxygenated (59.4–79.4%) and hydrocarbons (14.3–34.2%). The ranges of major constituents were as follow: carvacrol (14.1–77.6%), p-cymene (3.5–7.9%), γ-terpinene (3.8–6.6%) and α-pinene (1.2–7.8%). Leaves at post-flowering stage also contained a significant amount of borneol (16.3%) and thymol (27.8%). Essential oils obtained from flowering stage showed the highest antioxidant activity as measured by DPPH free radical scavenging ability, reductive potential and β-carotene/linoleic acid assays with IC50 values ranging from 61.48 ± 1.58 μg/mL to 182.86 ± 2.84 μg/mL for leaves and from 63.81 ± 1.96 μg/mL to 129.93 ± 6.16 μg/mL for flowers. The essential oils were also screened for antimicrobial activity against seven bacteria of significant importance for food hygiene and four pathogenic fungal strains. The results indicated that Candida strains were the most sensitive among the microorganisms tested (MIC values of 0.12–0.25 mg/mL) followed by Gram positive and Gram negative bacterial strains, with the Gram-negative Pseudomonas aeruginosa being the most resistant strain. The maximum antimicrobial activity was observed with oils obtained from the vegetative and flowering stages, which therefore represent the optimal harvesting times of this plant for application in the pharmaceutical and food industries.
    Industrial Crops and Products 01/2013; 49. · 3.21 Impact Factor
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    ABSTRACT: Thymus broussonetii, Thymus maroccanus and Thymus satureioides, are endemic Moroccan species that are intensively utilized because of their wide ranging medicinal and culinary properties. In an effort to preserve these over-exploited species, the effect of cultivation on the essential oil chemical composition, antioxidant and antimicrobial activities were investigated. The hydrodistilled oils obtained from wild and cultivated thyme species were analyzed by GC–MS. In total, 41 components were identified representing more than 98% of the oils, with carvacrol (26.0–71.6%), borneol (5.0–20.1%), γ-terpinene (4.0–8.9%) and p-cymene (5.2–10.3%) as the main constituents. Similar oil profiles were obtained from wild and cultivated T. maroccanus, whereas some quantitative differences were noted between oils obtained from wild and cultivated T. broussonetii and T. satureioides. The antioxidant and antimicrobial assays revealed that all oils tested from wild and cultivated studied thyme species showed strong activities.
    Industrial Crops and Products 01/2013; · 3.21 Impact Factor
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    ABSTRACT: The hydro-distilled essential oils obtained from aerial parts of the wild (w) and cultivated (c) mint timija (Mentha suaveolens subsp. timija), an endemic medicinal species of Morocco, have been analyzed by GC-MS and screened for antimicrobial activity. In total, 35 compounds representing more than 98% of the oils were identified. Menthone (39.4(w)-10.8(c)%), pulegone (62.3(c)-34.3(w)%) and isomenthone (9.3(c)-7.8(w)%) were found as the main components for the two oils. The volatiles of the wild and cultivated material differed significantly in both the percentage of the main components and antimicrobial effect. Pulegone was more dominant in cultivated mint timija (62.3%) than in wild one (34.3%), while menthone was more abundant in the wild material (39.4%). In the antimicrobial assays, both oils displayed good to excellent activity against all microorganisms tested with the oil of the cultivated form being more active.
    Natural product research 07/2012; · 1.01 Impact Factor
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    ABSTRACT: Samples of the aerial parts of Thymus broussonetii, T. ciliatus, T. leptobotrys, T. maroccanus, T. pallidus, T. satureioides, and T. serpyllum collected from different natural regions in southern and south-western Morocco were analyzed for their qualitative and quantitative essential oil profiles. In total, 46 compounds, representing more than 99% of the oils, were characterized. Monoterpenes, both hydrocarbons (12.9-58.0%) and oxygenated monoterpenes (38.8-81.1%), were the principal classes of compounds for most of the thyme species studied. Cluster analysis allowed the classification of the species into three main groups: a carvacrol group (Group I), comprising the species T. maroccanus and T. leptobotrys, a linalyl acetate and (E)-nerolidol group (Group II), represented by T. serpyllum, and a thymol and/or carvacrol, γ-terpinene, and p-cymene group (Group III), composed of T. satureioides, T. broussonetii, T. ciliatus, and T. pallidus. The essential oils were screened for their antioxidant and anticandidal activities. The data showed that the oils obtained from T. leptobotrys and T. maroccanus (carvacrol group) possessed the highest antioxidant activities as assessed by the determination of the DPPH free radical-scavenging ability and the ferric-reducing potential. The anticandidal assays indicated that the highest activity was noticed for the essential oil isolated from T. leptobotrys.
    Chemistry & Biodiversity 06/2012; 9(6):1188-97. · 1.81 Impact Factor
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    ABSTRACT: The composition of essential oils isolated from leaves of 11 natural populations of Cupressus atlantica, an endemic and endangered coniferous species from Morocco, was investigated by GC-MS. In total, 42 essential oil components were identified, accounting for 73.1-97.7% of the total oil. Monoterpene (25.2-84.9%) and sesquiterpene hydrocarbons (12.2-46.8%) were the principal subclasses of compounds, with α-pinene (15-65.4%), germacrene D (5.9-30.5%), δ-3-carene (2-16.6%) and γ-cadinene (1.3-9.8%) as the main constituents. The results of the oil composition were analysed by hierarchical cluster and principal component analysis that established three main groups of essential oils. These oils were differentiated by the content of the major constituents (α-pinene, germacrene D, δ-3-carene and γ-cadinene), geographical location and climatic characteristics.
    Natural product research 03/2012; · 1.01 Impact Factor
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    ABSTRACT: The essential oils of leaves and flowers of the wild and cultivated Moroccan Achillea ageratum L., a rare and threatened medicinal species, were examined by GC/MS, and their chemical compositions were compared. At least nine components were identified in both wild and cultivated A. ageratum oils, representing more than 95% of the oils. Artemisyl acetate (62.34-78.79%), yomogi alcohol (4.89-12.40%), santolina alcohol (4.86-11.77%), and artemisia alcohol (3.36-7.04%) were the major compounds. Terpene-alcohol proportion was higher in wild A. ageratum than in cultivated A. ageratum. The antibacterial analysis showed that both oils presented high activity against all the studied Gram-positive strains in a range of MIC values from 2.55 to 7.02 mg/ml, but they appeared not effective against the tested Gram-negative ones (MIC values 20.40-41.10 mg/ml). They also exhibited remarkable antifungal activities against Candida species with MIC values ranging from 5.83 to 8.42 mg/ml. From these results, it was concluded that domestication of this threatened medicinal species using clonal propagation did not significantly affect its chemical composition and consequently its antimicrobial properties.
    Chemistry & Biodiversity 03/2012; 9(3):598-605. · 1.81 Impact Factor
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    ABSTRACT: The title compound, C(20)H(28)O(3), was isolated during our investigation into the chemical composition and pharmacological activity of Centipeda cunninghamii (DC.) A. Braun & Asch. (Asteraceae). The enanti-opure compound, a diterpene with a carbon skeleton, is composed of three six- and one five-membered rings in chair, twist-boat, half-chair and envelope conformations, respectively. Each mol-ecule makes one intra- and one inter-molecular O-H⋯O hydrogen bond in the crystal lattice, forming hydrogen-bonded chains along [010]. The absolute configuration of the compound was assigned on the basis of optical rotation measurements.
    Acta Crystallographica Section E Structure Reports Online 02/2012; 68(Pt 2):o526-7. · 0.35 Impact Factor

Publication Stats

757 Citations
104.21 Total Impact Points

Institutions

  • 1999–2014
    • Southern Cross University
      • Southern Cross Plant Science
      Лизмор, New South Wales, Australia
  • 2011–2012
    • Cadi Ayyad University
      • Faculty of Sciences Semlalia
      Maraksh, Marrakech-Tensift-Al Haouz, Morocco
  • 2009
    • Murdoch University
      Perth City, Western Australia, Australia
  • 2008–2009
    • Henan Provincial People’s Hospital
      Cheng, Henan Sheng, China
  • 2007
    • University of Papua New Guinea
      • Department of Chemistry
      Port Moresby, National Capital District, Papua New Guinea
  • 2006
    • University of New South Wales
      • School of Chemistry
      Kensington, New South Wales, Australia
  • 1994–2006
    • University of Western Sydney
      Penrith, New South Wales, Australia
  • 2004
    • University of Hawai'i System
      Honolulu, Hawaii, United States