Determination of phenolic compounds and antioxidant test of aqueous extracts from the leaves and stems of Strophanthus sarmentosus dc (Apocynaceae), harvested in Mali

Plants represent an inexhaustible reservoir of bioactive molecules, characterised by great structural diversity and a broad spectrum of biological activities. Strophanthus sarmentosus ( Apocynaceae ) is a plant widely used in traditional African medicine, but one that remains largely unexplored from a phytochemical and pharmacological perspective. This plant contains several groups of secondary metabolites, including flavonoids, tannins, alkaloids and saponosides. The aim of this study was to assess the total phenolic and flavonoid content, as well as the antioxidant activity, of aqueous extracts from the leaves and stems of S. sarmentosus. Total polyphenol contents were determined using the Folin-Ciocalteu method, total flavonoid contents by colorimetric assay, and antioxidant activity was assessed using the DPPH free radical scavenging assay. The results showed that total polyphenol content ranged from 364.8 ± 52.3 mg GAE/g in the leaves to 339.6 ± 7.6 mg GAE/g in the stems. Total flavonoid contents ranged from 192.8 ± 14.7 mg CtE/g for the leaves to 72.4 ± 39.0 mg CtE/g for the stems. Antioxidant activity, expressed as the 50 per cent inhibitory concentration (IC₅₀) against the DPPH radical, was 40.03 ± 0.78 µg/mL for the leaves and 42.01 ± 1.07 µg/mL for the stems, values close to that of ascorbic acid, which was used as a positive control (IC₅₀ = 42.90 ± 2.37 µg/mL). These results indicate that the leaves and stems of S. sarmentosus are promising sources of phenolic compounds and exhibit significant antioxidant activity, justifying increased interest in this species in the search for new natural agents with therapeutic potential.