Phytochemical, antioxidant and antibacterial studies of extracts and chromatographic fractions of <i>Gmelina arborea</i> Roxb (Lamiaceae)

Antimicrobial resistance and oxidative stress are increasing and researchers are being encouraged to search the natural plant products, due to their popular usage in ethno-medicine, for alternative source of antimicrobial and antioxidant compounds. Gmelina arborea used in West-Africa and Ayurveda folkloric medicine to cure several diseases was therefore investigated for phytochemical, antioxidant and antimicrobial activities. Extracts and chromatographic fractions of the root-bark tested for antibacterial activity with the MIC determined on seven selected bacteria using agar dilution method. The antioxidant capacity of the crude extracts was determined by six (6) methods: total flavonoid content, total phenolic content, ferric reducing power, total antioxidant capacity, Trolox equivalent antioxidant capacity and DPPH (2,2-diphenyl-1-picryhydrazyl) properties. Phytochemical screening indicated the presence of saponins, tannins, flavonoids, terpenoids anthraquinones, phenols and alkaloids. The methanol and ethyl-acetate extracts of the plant showed good antibacterial activities (18 mm inhibitory zones and MIC and MBC 12.5–100 mg/mL) against P. aeruginosa ATCC 27853 and S. aureus ATCC 6571. Antioxidant study of the extracts revealed that both ethyl acetate and methanol extracts have good antioxidant capacity comparable to that of ascorbic acid standard. Therefore, Gmelina arborea could prove a valuable source of developing new antimicrobial and antioxidant compounds for therapeutic uses.