Résumé:
Medicinal plants are important natural sources for a wide variety of bioactive substances. This work focused on the valorization of three Algerian medicinal plants namely Phagnalon rupestre, Teucrium polium and Zygophyllum album for qualitative and quantitative estimation of phenolic compounds, identification of their phytochemical composition in some secondary metabolites, and their antioxidant activities estimation.
A screening study for the main secondary metabolites of the studied plants was established, as well as a colorimetric quantification of the total polyphenol contents (by the Folin-Ciocalteu method), total flavonoid contents (by the aluminum trichloride method), condensed tannins (by the vanillin method) and hydrolysable tannins (by the ferric chloride method). The quantitative determination detected in the aqueous extract of T.polium and P.rupestre demonstrated the higher contents in polyphenols (105,21 ± 2,5 ; 90,97 ± 1,7 mg/g, respectively), in flavonoids (94,63 ± 0,5 ; 71,73 ± 0,7 mg/g, respectively), in condensed tannins (1,33 ± 0,2 ; 1,19 ± 0,5 mg/g, respectively), and in hydrolysable tannins (22,79 ± 0,7 ; 20,4 ± 0,7 mg/g, respectively). However, the aqueous extract of Z.album contains the lowest concentrations. The results of phytochemical assays by coloring reaction methods for the studied extracts show the presence of various phytoconstituants with predominance of polyphenols.
Simultaneously with the phytochemical analysis, the antioxidant activity of the aqueous extracts was tested in vitro by three different tests: the anti-radical action against the 2,2-diphenyl-1-picrylhydrazyl radical ( DPPH), the reductive power assay (FRAP), and β-carotene assays. The extracts showed a strong antioxidant power with the DPPH assay with EC50 vary between 13,53 ± 0,01 μg/mL for T. polium, and 572,8 ± 0,1 μg/mL for Z. album. Regarding the FRAP assay, the EC50 values vary between 42,6 ± 0,001 in T. polium and 741,9 ± 0,02 μg/mL in Z. album. For the β-carotene assay, the aqueous extracts of T. polium and P. rupestre show the highest activity compared to the authentic substance of Trolox and give EC50value of 5,24 ± 0,005 and 5,35 ± 0,005 μg/mL, respectively. They are, therefore, a source of natural antioxidants. The potent antioxidant activity of T.polium and P.rupestre may be related to their high levels of phenolic compounds. The active effect of these plants suggested that these species could be used in the food, cosmetic and pharmaceutical industry fields.
