RESUMELes radicaux libres étant impliqués dans la genèse de plusieurs maladies, l'intérêt porté à la recherche d'antioxydants naturels a considérablement augmenté ces dernières années. L'objectif de cette étude était d'évaluer l'activité antioxydante des extraits hydro-éthanoliques des feuilles et écorces de Piliostigma thonningii. La détermination de la teneur en polyphénols a été effectuée par la méthode de Folin Denis. L'activité antiradicalaire a été évaluée par les tests de réduction du DPPH (2, 2-diphenyl-l-picrylhydrazyl) et de l'ABTS (acide 2,2'-azino-bis-(3-éthylbenzothiazoline-6-sulfonique)). Le pouvoir réducteur vis-à-vis de l'ion ferrique a été également évalué. Il ressort de ces tests que les écorces sont environ deux fois plus riches en polyphénols que les feuilles. Les CI50 des extraits des écorces et des feuilles sur DPPH sont respectivement de 46,8 ± 5,77 µg/ml et 138,9 ± 2,03 µg/ml. Concernant le test ABTS les CI50 des deux extraits sont 39,3 ± 1,00 µg/ml et 109 ± 6,25 µg/ml respectivement. Le pouvoir réducteur des écorces est supérieur à celui des feuilles à toutes les concentrations testées. Donc les écorces présentent une activité antioxydante meilleure que celle des feuilles de cette plante. © 2017 International Formulae Group. All rights reserved.Mots clés : Piliostigma thonningii, activité antioxydante, phénols totaux.Evaluation of the antioxidant activity of hydro-ethanolic leaf and bark extracts of Piliostigma thonningii Schumach ABSTRACT Free radicals are involved in the genesis of several diseases, what makes increasing research for natural antioxidants in recent years. The purpose of this study was to evaluate the antioxidant activity of the hydro-ethanolic leaf and bark extracts of Piliostigma thonningii. The polyphenol content was determined with Folin Denis reagent. The antiradical activity was evaluated using S. I. M. DIENG et al. / Int. J. Biol. Chem. Sci. 11(2): 768-776, 2017 769 DPPH (2, 2-dipheny l-picrylhydrazyl) and ABTS (2,2'-azino-bis-(3-ethylbenzothiazolin-6-sulfonic acid) reduction tests. The reducing power was also performed using ferric reducing. (FRAP). All experiments were done in triplicate. From these tests, it appears that the bark is approximately twice as rich in polyphenols as the leaves.The IC50 of the bark and leaf extracts on DPPH are respectively 46.8 ± 5.77 μg/ml and 138.9 ± 2.03 μg/ml. On ABTS test, bark and leaf extracts had exhibited scavenger activity with respective IC50 values 39.3 ± 1.00 μg / ml and 109 ± 6.25 μg / ml. Reducing power of bark extract was higher than that of leaf extract at all tested concentrations. Therefore, the bark exhibits a better antioxidant activity than that of the leaves of this plant.

The chemical diversity of Zanthoxylum zanthoxyloides growing wild in Senegal was studied according to volatile compound classes, plant organs and sample locations. The composition of fruit essential oil was investigated using an original targeted approach based on the combination of gas chromatography (GC) and liquid chromatography (LC) both coupled with mass spectrometry (MS). The volatile composition of Z. zanthoxyloides fruits exhibited relative high amounts of hydrocarbon monoterpenes (24.3 - 55.8%) and non-terpenic oxygenated compounds (34.5 - 63.1%). The main components were (E)-β-ocimene (12.1 - 39%), octyl acetate (11.6 - 21.8%) and decanol (9.7 - 15.4%). The GC and GC/MS profiling of fruit essential oils showed a chemical variability according to geographical locations of plant material. The LC/MS/MS analysis of fruit oils allowed the detection of seven coumarins in trace content. The chemical composition of fruit essential oils was compared with volatile fractions of leaves and barks (root and trunk) from the same plant station. Hexadecanoic acid, germacrene D and decanal were identified as the major constituents of leaves whereas the barks (root and trunk) were dominated by pellitorine (85.8% and 57%, respectively), an atypic linear compound with amide group. The fruit essential oil exhibited interesting antimicrobial activities against Staphylococcus aureus and Candida albicans, particularly the alcohol fraction of the oil.

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