Condensed Tannins Content and their Influence on the Antioxidant Activity of Bark Hydroethanol Extract of Piliostigma reticulatum (Dc) Hochst and its Fractions

Background: Consumption of natural products from plants is implicated in the reduction of the occurrence of diseases related to oxidative stress. Piliostigma reticulatum is a plant well known to traditional practitioners in Senegal where leaves and bark are often used against many diseases, such as ulcers, boils, syphilitic cancer, toothache, gingivitis and diarrhea. Aim: This study compared hydroethanol extract from the plant bark and its fractions by assessing their total phenol contents, antioxidant activity and the influence of condensed tannins on their activity. Method: barks were extracted by a moderate decoction with ethanol-water followed by a silica column fractionation with successively ethyl acetate, methanol and water. For this study, assays were carried out before and after precipitation of tannins by BSA and PVPP tests. Total phenol and condensed tannins of hydroethanolic extract and its fractions were performed by Folin Ciocalteu and hydrolysis methods. Antioxidant activity was evaluated by DPPH and CUPRAC tests. Results: Tannins precipitation leads a light decrease of total phenol and condensed tannins contents of samples. Total phenol content of hydroethanolic extract was 51.2 mg GAE/g vs 3.2 after BSA test and 1.7 after PVPP test whereas condensed tannins content obtained 72.2% vs 4.2% and 2.3% after precipitation. Antiradical activity was lost following the elimination of tannins with IC₅₀: 5.33 ± 0.04 mg/l vs 78.86 ± 0.92 after BSA and > 500 after PVPP. Conclusion: This results showed the condensed tannins would be in charge of antiradical and reducing activities of plant barks and PVPP precipitated much better the tannins from those extracts than BSA.