In vitro antioxidant activity, brine shrimp lethality and assessment of bioactive constituents of three wild Dioscorea species

Abstract

Many yam (Dioscorea L.) species serve as staple foods in many parts of the world. They are known to show strong enzymatic browning reactions and some species are reported to be toxic. The present study focuses on the cytotoxicity screening using brine shrimp lethality activity (BSLA) and antioxidant evaluation of peel and flesh extracts of Dioscorea hirtiflora, D. dumetorum wild and varieties of D. bulbifera. The qualitative phytochemical assessment of the bioactive extracts of the yam species was also done. Powdered samples of the three plants were successively extracted using n-hexane, dichloromethane (DCM), ethylacetate (EtOAc) and methanol (MeOH). Cytotoxicity of extracts was evaluated using BSLA, antioxidant activity was measured using 1,1-diphenyl-2-picryl-hydrazyl (DPPH), while qualitative assessment of bioactive constituents was done by thin layer chromatography (TLC). The DCM extract of the peel of wild D. dumetorum had maximum cytotoxicity (125.4 µg/mL) compared with standard cytotoxic drug—cyclophosphamide (531 µg/mL) and gallic acid (323.6 µg/mL). The MeOH extract of the flesh of D. hirtiflora (IC50 11.8 µg/mL) compared with standards—ascorbic acid (IC50 6.90 µg/mL) and gallic acid (IC50 8.60 µg/mL) exerted the highest radical scavenging activity. Total phenolic content (14.00 mg GAE/g) and Total flavonoid content (74.4 mg QE/g) were higher in the EtOAc extract of the flesh extract of D. bulbifera (mauve) than in other species. The TLC plates showed characteristic colours with visualizing reagents, which confirmed the presence of alkaloids, phenolics and flavonoids. The presence of these metabolites could account for the cytotoxicity and the antioxidant activities of the yam species. The results from the study could justify the applications of the yam species as both food and medicines in traditional health care system.