Phytochemical and antioxidant assessments of Dioscorea bulbifera stem tuber

Background: Dioscorea bulbifera (D. bulbifera) is used in traditional medicine for the treatment of many disease conditions. However, there is a paucity of information on the antioxidant potential of its stem tuber. Methods: The antioxidant activity of the methanolic extract of D. bulbifera stem tuber was evaluated by measuring its ability to scavenge 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical, superoxide anion radical (O2-) and nitric oxide (NO) radical. It was also analyzed for bioactive secondary metabolites using standard qualitative and quantitative spectrophotometric methods. Results: The extract showed total phenolic content (0.243 ± 0.052 mg) gallic acid equivalent compared to tannins content (0.259 ± 0.034 mg). Low flavonoid contents (0.060 ± 0.025 mg) quercetin equivalent (QE) and high flavonol contents (1.399 ± 0.075 mg) QE were found in the extract. The extract showed a potent concentration-dependent DPPH radical inhibitory potential with maximal inhibition activity (69.39 ± 1.62%) at 5000 μg/mL compared to ascorbic acid with maximal inhibition activity (88.9 ± 2.67%) at the same concentration. The extract produced maximal O2- anion inhibitory activity (52.86 ± 0.68%) at 2500 μg/mL compared to quercetin with maximal inhibitory activity (68.23 ± 0.41%) at the same concentration. The extract exhibited NO activity in a dose-depend fashion when compared to α-tocopherol. Conclusion: These results showed that D. bulbifera stem tuber extract contains bioactive secondary metabolites with potent-free radical scavenging activity, which could be extracted and standardized for use as food, medicine, and in industries.