Martin Benoit Ngassoum

Antimicrobial study of essential oils of Ocimum gratissimum leaves and Zanthoxylum xanthoxyloides fruits from Cameroon.

An investigation of antimicrobial activities of essential oils of fresh leaves of Ocimum gratissimum and the essential oil of the dried fruits of Zanthoxylum xanthoxyloides was carried out. The essential oils showed extensive inhibition zones and are, therefore, effective antimicrobial systems.

Chemical composition of essential oils of Lantana camara leaves and flowers from Cameroon and Madagascar

The essential oils of leaves and flowers of Lantana camara (Verbenaceae) from Cameroon and Madagascar were analysed by GC–FID and GC–MS. The oils are characterized by a high percentage of sesquiterpenes. The major components in the oils from Cameroon are ar-curcumene (25%), β-caryophyllene (13%) and caryophyllene epoxide (7%), while the main components of the oil from Madagascar are davanone (15%) and β-caryophyllene (12%). The monoterpenes percentages are lower in the two essential oils and are represented by sabinene (1–9%), α-pinene (2–4%), 1,8-cineole (1–3%) and linalool (1–3%). A comparison with the composition of various essential oils of L. camara with different origin will also be given. Copyright

Toxicity of some terpenoids of essential oils of Xylopia aethiopica from Cameroon against Sitophilus zeamais Motschulsky

Abstract:  The acute toxicity of essential oils from the whole fruit (EF) or from the fibres of the fruit (FF) of the local aromatic plants Xylopia aethiopica Dunal (Annonaceae) collected in north Cameroon was evaluated on Sitophilus zeamais adults. A concentration of 1 ml of essential oil per 100 g of maize seeds was tested to determine weevil mortality after 24 h of exposure. Under these conditions, the essential oil derived from both EF and FF of X. aethiopica led to 100% mortality. In a second step, proportions of active compounds present in the oil of both EF and FF of X. aethiopica were quantified. The toxicity of the four main compounds was tested against S. zeamais: α‐pinene, β‐pinene, Δ‐3‐carene and terpinen‐4‐ol according to their proportion in the essential oil of the concerned plant part. β‐pinene and terpinen‐4‐ol were responsible for 50% of the mortality at the proportion found in EF and FF essential oils respectively. When mixed, a synergic effect of the compounds was observed that restored the mortality percentage observed for the crude oil. It appears that X. aethiopica essential oil could be a potential source of natural and low‐cost insecticide to control storage pests.

Identification of soil bacteria able to degrade phenanthrene bound to a hydrophobic sorbent in situ.

Efficient bioremediation of PAH-contaminated sites is limited by the hydrophobic character and poor bioavailability of pollutants. In this study, stable isotope probing (SIP) was implemented to track bacteria that can degrade PAHs adsorbed on hydrophobic sorbents. Temperate and tropical soils were incubated with (13)C-labeled phenanthrene, supplied by spiking or coated onto membranes. Phenanthrene mineralization was faster in microcosms with PAH-coated membranes than in microcosms containing spiked soil. Upon incubation with temperate soil, phenanthrene degraders found in the biofilms that formed on coated membranes were mainly identified as Sphingomonadaceae and Actinobacteria. In the tropical soil, uncultured Rhodocyclaceae dominated degraders bound to membranes. Accordingly, ring-hydroxylating dioxygenase sequences recovered from this soil matched PAH-specific dioxygenase genes recently found in Rhodocyclaceae. Hence, our SIP approach allowed the detection of novel degraders, mostly uncultured, which differ from those detected after soil spiking, but might play a key role in the bioremediation of PAH-polluted soils.

Effect of Site Location and Collecting Period on the Chemical Composition of Hyptis Spicigera Lam. an Insecticidal Essential Oil from North-Cameroon

Abstract Hyptis spicigera essential oils from seven localities in the North-Cameroon (Ngaoundere, Guirvidig, Kodeck, Lara, Toloum, Kaele, Tchecal-baila) were investigated by GC and GC/MS. Results showed differences within harvesting sites and between the different sites of collection but did not revealed clear tendencies in the evolution of the oil composition with regard to the sampling period. The main group of compounds in all the analyzed samples were: α-pinene (11.9%-42.1%), β-pinene + sabinene (6.0%-39.8%) and β-phellandrene + 1,8-cineole (8.8%-27.4%) except in one oil where β-caryophyllene (23.4%) was the principal component. The insecticidal activity of H. spicigera and its principal terpenic components was evaluated against the cowpea weevil Callosobruchus maculatus F., the major cause of damages of cowpea (Vigna unguiculata (L.) Walp) in North Cameroon.

Composition and Antimicrobial Activity of Cymbopogon giganteus (Hochst.) Chiov. Essential Flower, Leaf and Stem Oils from Cameroon

Abstract The essential oils of fresh flowers (2 samples), leaves and stems of Cymbopogon giganteus (Hochst.) Chiovenda from Cameroon were investigated by GC and GC/MS. More than 55 components have been identified in the samples 1 (flowers 1), 2 (leaves), 3 (stems) and 4 (flowers 2) with main compounds possessing the p-menthadiene skeleton as follows: cis-p-mentha-1(7),8-dien-2-ol (1: 22.8%, 2: 27.7%, 3: 29.1%, 4: 20.5%), trans-p-mentha-1(7),8-dien-2-ol (1: 24.9%, 2: 21.6%, 3: 28.1%, 4: 26.5%), trans-p-mentha-2,8-dien-1-ol (1: 17.3%, 2: 22.1%, 3: 21.4%, 4: 16.3%) and cis-p-mentha-2,8-dien-1-ol (1: 8.3%, 2: 5.4%, 3: 4.6%, 4: 9.7%). Additional components in higher concentrations, responsible for the characteristic aroma impressions of these samples are especially limonene, trans-verbenol and carvone as well as some other mono- and sesquiterpenes. Antimicrobial activities of the four oils were found against Gram-(+)- and Gram-(-)-bacteria as well as the yeast Candida albicans, and these results were discussed with the compositions of each sample.

Investigation of Essential Oils of Plectranthus glandulosus Hook f. (Lamiaceae) from Cameroon

Abstract The essential oil of fresh and dried leaves of Plectranthus glandulosus Hook f. [syn. Coleus laxiflorus (Benth.) Roberty] from Cameroon were analysed by GC and GC/MS. The oils were characterized by a high percentage of oxygenated monoterpenes (58.6% and 84.6% respectively) represented by cis-piperitone oxide (3.0% and 35.1%), trans-piperitone oxide (0.5% and 12.6%), fenchone (30.8% and 21.6%) and piperitenone oxide (10.9% and 6.0%). The main monoterpene hydrocarbons were terpinolene (25.2% and 7.7%), limonene (3.2% and 1.7%) and myrcene (2.2% and 1.6%). The sesquiterpene derivatives were found in a very low percentage (< 2.5%), represented mainly by germacrene D (1.4% and 1.0%).

Investigation of the Essential Oil and Headspace of Laggera pterodonta (DC.) Sch. Bip. ex Oliv., a Medicinal Plant from Cameroon

Abstract The essential oils of leaves and flowers of Laggera pterodonta (Asteraceae) from Cameroon were analyzed by GC and GC/MS. The oils were characterized by a high percentage of oxygenated sesquiterpenes (30–80%) and thymol derivatives (4–50%). The major components in the oils were γ-eudesmol (17–45%), α-eudesmol (4–15%), 2,5-dimethoxy-p-cymene (4–50%) and juniper camphor (4–12%). Monoterpenes are found in a high percentage in the flower headspace, represented mainly by γ-terpinene (32%), terpinen-4-ol (14.1%) and β-phellandrene (6%).

Essential Oil and Headspace from Hyptis suaveolens (L.) Poit. Leaves and Flowers from Cameroon

Abstract The essential oils of the leaves, flowers and leaf stems of Hyptis suaveolens (L.) (Lamiaceae) from Cameroon were analyzed by GC, GC/MS and olfactometry. The oils and headspace were characterized by a high percentage of monoterpenes. The main monoterpenes in the oils and headspace were sabinene (9.3–42.2%), β-pinene (3.4–9.6%), limonene (3.2–8.0%) and p-cymene (2–3%). The sesquiterpenes were represented by β-caryophyllene (2–14%) and cis-α-bergamotene (2–3%). The oils contained also a high number of oxygenated monoterpenes and sesquiterpenes of low concentration. Some diterpenes have been identified in the oil of if H. suaveolens, particularly ar-abietatriene (2–6%), ar-abietatriene-19-ol (1%) and abietinol (1%).

Survey of pesticide residues in maize, cowpea and millet from northern Cameroon: part I

In northern Cameroon, the misuse of pesticides for pest control is common among small-scale farmers. Therefore, monitoring of pesticide residues was carried out on stored maize, cowpea and millet from eight localities. The determination of residues of organochlorines (lindane, α-endosulfan and β-endosulfan), organophosphorus compounds (malathion and pirimiphos-methyl), synthetic pyrethroids (permethrin) and carbamates (carbufuran) was performed using GC–ECD/NPD and GC–MS for confirmation. Organochlorine pesticides were detected more frequently and in higher concentrations, ranging from 0.02 ± 0.01 mg kg−1 for β-endosulfan in millet to 9.53 ± 4.00 mg kg−1 lindane in maize, than organophosphorus compounds, with concentrations varying from 0.04 ± 0.03 mg kg−1 for pirimiphos methyl to 0.23 ± 0.38 mg kg−1 for malathion in maize. Permethrin was found only in maize at 0.39 ± 0.23 mg kg−1. No carbofuran was found. More than 75% of samples contained pesticide residues above the maximum residue limit (MRL); showing a potential human dietary risk related to consumption of these grains.