Contribution à l’étude phytochimique et à l’évaluation de quelques activités biologiques des extraits des graines de Nigella sativa L.

Abstract

Nigella is an aromatic plant widelyused in traditional medicine in Algeria, it presents many active principles known by theirtherapeutic properties. In the present study, methanolic and aqueous extracts of Nigella Sativa L. seeds were studied to quantify their polyphenol and flavonoid contents using Folinciocalteu and AlCl3, respectively. In addition, the antioxidant activity is also tested by the DPPH radical reduction method. In addition, the antibacterial power of these extracts was studied by the solid-state diffusion method, on reference bacterialstrains. The qualitative analysis of theseextracts by the preliminary tests revealed the presence of phenolic compounds, tannins and flavonoids; thisisconfirmed by a quantitative analysisbased on the dosage of the latter. The qualitative analysis of these three extracts by TLC revealed the presence of numerous constituents among which: gallicacid, quercetin and vanillin. Wetried on the analysis of these extracts which revealed the richness of the extract AQ and METI and METII in phenolic compounds which confirms the results of the dosage of polyphenols by the method of Folin-Ciocalteu, where the contents are respectively: 2.35, 0.058 and 0.82 μg EAG/mg and in flavonoidswith contents of 0.211, 1.29 and 0.322 μg/mg Similarly, the quantitative evaluation of the antioxidant power of theseextracts, confirmsthat the methanolic extract by maceration showed better DPPH-inhibitory antiradical activity with the lowest IC50 (14.71 μg/ml) followed by the methanolic extract by soxhlet (IC50 33.82 μg/ml) and the aqueous extract with IC50 (80.75 μg/ml). Regarding the antimicrobial activity, the methanolic and aqueous extracts of Nigella Sativa L. seeds showed an appreciated antimicrobial effect by inhibiting the growth of different pathogenic strains (Pseudomonas aeruginosa and Staphylococcus aureus). While, no antibacterial effect was revealed in the strains (Klebsiella pneumoniae and Enterococcus faecalis. All these results highlight the different therapeutic applications of this plant in traditional medicine and encourage the search for new natural molecules with antioxidant and antibacterial properties, with the aim of investing them in different industries: pharmaceutical, cosmetic, food, etc.