Evaluation of antioxidant activity of hydromethanolic extracts of some medicinal species from South Algeria

Background: Phytochemicals are found in abundance at different levels in many medicinal plants. It is important to measure the total phenolic compounds correctly in such medicinal plants, the better to assess their antioxidant capacity. Methods: Our study sought to evaluate the total phenolic, flavonoid, and tannin contents of three Algerian medicinal plants: Echium pycnanthum Pomel, Haloxylon articulatum Boiss, and Solenostemma oleifolium Bull. & Bruce. We employed six different testing methods to help ascertain whether these compounds have an antioxidant capacity, including total antioxidant capacity, 1,1-diphenyl-2-picrylhydrazyl·≡, 2,2′-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid·≡+, β-carotene, reducing, and chelating assays. Results: Our study showed that these medicinal plants exhibited significantly different total polyphenol contents varying from 27.3 ± 2.1 mg to 120.3 ± 5.6 mg gallic acid equivalents/g dry weight. The phenolic content in H. articulatum was superior to those in E. pycnanthum and S. oleifolium. The same tendency was observed for the relative amounts of flavonoids and condensed tannins in the three medicinal plants. The antioxidant activities varied greatly among the different plants used in this study. Indeed, H. articulatum shoots exhibited the strongest antioxidant activity, with the lowest IC50 (6.3 ± 0.25 μg/mL) and EC50 (0.21 ± 0.01 mg/mL) values for 1,1-diphenyl-2-picrylhydrazyl·≡ and iron reducing tests, respectively. In addition, the superiority of this plant was more marked as compared to positive controls. Strong and positive correlations were found between phenolic classes and antioxidant activities with a correlation coefficient reaching R ≥ 0.99. Conclusion: This investigation confirmed that several medicinal herbs from South Algeria possess high in vitro antioxidant potency. Overall, our results can be considered very promising in the continuing effort to utilize plant species successfully for medicinal purposes in humans, providing further justification for the hypothesis that phenolic compounds in these plants can provide substantial antioxidant activity