Antioxidant and antimicrobial activities of Dialium guineense (Willd) leaf extract

Abstract

The in vitro antioxidant and antimicrobial activities of methanolic leaf extract of Dialium guineense were studied in order to provide a pharmacological basis for their ethomedicinal applications. Antioxidant activity was measured using 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging activity and reducing power assay. In addition, the total phenolic content was also analyzed. Antimicrobial activity was tested against clinical isolates of Staphylococcus aureus, Streptococcus mutans, Escherichia coli, Bacillus cereus, Pseudomonas aeruginosa, Klebsiella pneumoniae, Proteus mirabilis, Salmonella typhi, Candida albicans, Microsporium gypseum, Trichophyton mentagrophytes and Trichophyton rubrum using agar well diffusion method. The results of the DPPH scavenging activity of the extract showed a concentration dependent antioxidant activity with maximum scavenging activity (85.35%) observed at 250 μg/ml concentration and comparable to those of ascorbic (95.75%) and gallic acids (93.67%). The reducing potential of the extract (0.069 ± 0.003 nm) was also comparable to that of gallic acid (0.078 ± 0.022 nm), while the total phenolic content was 69.45 ± 0.002 mg/g gallic acid equivalent. The antimicrobial inhibition zone and minimum inhibitory concentration values of the extract ranged between 10.2 to 25.9 mm and 7.81 to 62.5 μg/ml respectively, with the Gram positive bacteria generally being most sensitive, followed by the fungi and the Gram negative bacteria. This study indicates that D. guineense leaf extract has significant antioxidant and antimicrobial properties, and thus substantiates its popular and wide traditional applications in diverse ailments. The plant may therefore be exploited as a potential preservative in the pharmaceutical and food industries.

Keywords: Dialium guineense, antioxidant properties, DPPH assay, total phenolics, gallic acid.