Determination of total phenolic and flavonoid contents, antioxidant and antibacterial potential of the bark extracts of Syzygium guineense (Wild.) DC

Abstract

Background: Syzygium guineense (Wild.) DC. is a wild indigenous tree widely used as a traditional medicine for various human ailments in Ethiopia. The purpose of this study was to quantify total phenolic (TPC) and total flavonoid (TFC) contents and determine antioxidant and antibacterial activities of various solvent extracts of the bark of the plant. Methods: The TPC and TFC were determined using Folin-Ciocalteu and aluminum chloride methods, respectively. The 2, 2-diphenyl-1–picrylhydrazyl (DPPH) scavenging, ferric reducing power (FRAP) and total antioxidant capacity (TAC) assays were used to evaluate the antioxidant activities. Antibacterial properties were determined using the disc-diffusion assay based on minimum inhibitory concentration (MIC) against four bacterial strains (Klebsiella pneumoniae, Escherichia coli, Staphylococcus aureus, and Salmonella typhimurium). Results: The ethanol extract of the bark was found to have high TPC (37.80 ± 3.70 mgGAE/g) and TFC (19.22 ± 1.44mgQE/g). Similarly, the ethanol extract showed stronger DPPH scavenging activity (EC50=5.62 µg/mL). The FRAP and TAC were also strong (163.08±11.67 mgAAE/g and 143.72±2.86 mgBHTE/g of dried extract of 1 mg/mL, respectively). The lowest MIC was observed in acetone extract against S. aureus and in ethanol extract against K .pneumoniae. The chloroform extract was impotent against all microbial strains. Conclusion: The bark of S. guineense possesses high TPC and TFC and strong FRAP and TAC asserting high antioxidant contents. The extracts have shown antibacterial activities against both Gram positive and Gram negative bacterial species. Thus, further in-depth investigations may warrant the isolation of powerful antioxidants and potent antimicrobial agents from the plant.