Screening phytochimique et étude de l’activité antioxydante de trois plantes médicinales de la pharmacopée traditionnelle du Niger : Vernonia amygdalina Del., Tephrosia purpurea (L.) et Momordica ba

Considering the potential role in food industry and human health, antioxidants are gaining popularity all across the globe. Antioxidants are defined as a substance that even in small amounts, is capable of preventing or delaying the oxidation of easily oxidizable materials. In this work, different parts of three plant species of the Niger Pharmacopoeia (Vernonia amygdalina Del., Tephrosia purpurea (L..) and Momordica balsamina (L..) were studied. Tube characterization reactions were used for phytochemical screening. The Folin-Ciocalteu and aluminium trichloride methods were used to determine the total polyphenol and flavonoid content. The antioxidant activity of the various crude extracts was determined through DPPH tests. Two types of extraction were used for these tests : maceration and decoction, and raw extracts were used for the work. The results of phytochemical screening showed on the different plants parts indicate the presence of various chemical groups, including polyphenols, tannins, saponins, flavonoids, alkaloids, saponosides, and others.. The compounds were quantified by spectrophotometry. Quantification of the compounds by spectrophotometry showed that the aqueous extracts of the bark and leaves of Vernonia amygdalina were the richest in polyphenols (57.05±0.33 mg EAG/g and 47.062±0.88 mg EAG/g, respectively), while the hydroethanolic and ethanolic extracts of the leafy branches of Tephrosia purpurea were the richest in total flavonoids (13.79±0.28 mg EQ/g and 13.73±0.12 mg EQ/g respectively). In terms of antioxidant power, the results obtained showed that the extract of Vernonia amygdalina bark exhibited the highest antioxidant activity with an inhibitory concentration (CI50=0.0023mg/ml). Our findings showed that the aqueous extracts of these plants have antioxidant properties; which substantiated their utilization in the conventional management of specific ailments. Key words : Vernonia amygdalina, Momordica balsamina, Tephrosia purpurea, Antioxidants, Niger.