Phytochemical analyses, antimicrobial and antioxidant activities of stem bark extracts of Distemonanthus benthamianus H. Baill. and fruit extracts of Solanum torvum Sw. from Gabon

Abstract

To evaluate the phytochemical constituents, antimicrobial and antioxidant activities of the extracts of Distemonanthus benthamianus (D. benthamianus) stem bark and Solanum torvum (S. torvum) fruit which have been used as traditional medicinal herbs in Gabon. Methods: Plant extracts were subjected to a qualitative study (phytochemical screening) and a quantitative (dosing) study of secondary metabolites. Antioxidant activity was tested by 1,1- diphenyl-2-picrylhydrazyl and 2,2'-azino-bis 3-ethylbenzothiazoline-6-sulfonic acid assay. Bacteria and fungi susceptibility tests were performed on Mueller Hinton medium and solid Sabouraud, respectively, using the diffusion method, while minimum inhibitory concentration, minimum fungicidal concentration and minimum bactericidal concentration were evaluated by microdilution method. Results: The total phenol and tannin contents were significantly higher in the water-ethanol extract compared to the other extracts of D. benthamianus and S. torvum. The water-ethanol and water-acetone extracts showed significantly higher antioxidant activity than the aqueous extracts of the two medicinal plants. However, the extracts presented weak antioxidant activities compared to standards (Vitamin C, BHA). The water-acetone and water-ethanol extracts of S. torvum showed the highest antimicrobial activity against Bacillus cereus LMG 13569 BHI, Shigella dysenteriae 5451 CIP, Shigella dysenteriae and Neisseria gonorrhoeae. Conclusions: Our results show that D. benthamianus and S. torvum can be promising sources of natural products with potential antimicrobial and antioxidant activities.