Phytochemical Profile, Antiradical and Antioxidant Capacity of Leaves and Stems of Landolphia owariensis P.Beauv. (Apocynaceae): Valorization of an Ivorian Plant

Objective: This study aims to investigate the phytochemical composition and antioxidant capacity of the leaves and stems of Landolphia owariensis P.Beauv. Methodology: A qualitative and quantitative phytochemical screening was carried out using colorimetric tests, along with the determination of total phenols, total flavonoids, condensed tannins, iridoids, and alkaloids. The radical scavenging and antioxidant activities were evaluated using DPPH and FRAP assays on both crude methanolic extracts and selective ethyl acetate extracts of the leaves and stems of Landolphia owariensis P.Beauv. The extraction yields obtained from leaves and stems of Landolphia owariensis P.Beauv. varied between 14.22% and 17.68%. Methanolic maceration of the leaves (MFM: 17.68%) produced significantly higher yields than the stems (MTM: 15.77%), and a similar trend was observed in methanolic decoction (DFM: 16.18% vs. DTM: 14.22%). Qualitative phytochemical screening revealed the presence of alkaloids, flavonoids, iridoids, phenolic compounds, and condensed tannins. Quantitative analysis showed that the concentrations of total phenols, flavonoids, condensed tannins, iridoids, and alkaloids varied depending on the solvent and extraction method. Total phenols were more abundant in stem extracts (DTM: 779.64 ± 1.23; MTM: 972.39 ± 2.63 mg GAE/g DW) compared to leaf extracts (DFM: 376.05 ± 3.44; MFM: 477.59 ± 2.43 mg GAE/g DW). Flavonoids were predominantly found in leaves (DFM: 978.64 ± 3.60; MFM: 874.53 ± 3.38 mg QE/g DW), while condensed tannins were more concentrated in stems (DTM: 221.86 ± 2.52; MTM: 188.16 ± 1.52 mg CE/g DW). Iridoids showed moderate and consistent concentrations across organs, and alkaloids displayed low and comparable levels (16–17 mg/g DW). The DPPH assay indicated that the stem macerate in methanol (MTM) was the most effective crude extract with an IC₅₀ of 11.195 µg/mL, while the FRAP assay confirmed its highest reducing power (MTM: 1505.727 mM FeSO₄/g), followed by the stem decoction (DTM: 1240.179 mM FeSO₄/g). Conclusion: This study establishes that Landolphia owariensis P.Beauv constitutes a rich source of specialized metabolites with antioxidant properties, thus validating its therapeutic use in traditional medicinal practices.