Antioxidant and Antimicrobial Properties of Ethanolic Extract of Lemon Verbena

Chemical preservatives are commonly used to prevent food from quick spoiling and oxidizing. Despite their effect in increasing shelf life of foods, these compounds can have side effects. Residues of chemical compounds in foods increase microbial resistance. This study aims to investigate the antioxidant and antimicrobial properties of lemon verbena (Lippia citriodora L.) ethanolic extract against some gram-positive and gram-negative bacteria.

In this experimental study, The soaking method and ethanol solvent was used for extraction. Antioxidant activities of different concentrations of extract were assessed using DPPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenging activity test and compared with butylated hydroxyanisole (BHA) as a synthetic antioxidant. Antimicrobial effect of extract on Staphylococcus aureus, Listeria innocua, Bacillus cereus, Escherichia coli, Pseudomonas aeruginosa and Salmonella typhimurium was determined by disk diffusion and well diffusion methods and measuring minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). Experimental data were analyzed in SPSS software, version 20 using analysis of variance and the mean values were compared using Duncan’s multiple range test.

The amounts of phenols and flavonoids in the ethanolic extract of were 96.47±0.35 mg of gallic acid/g of extract and 31.07±0.42 mg of quercetin/g of extract, respectively. The half-maximal inhibitory concentration of lemon verbena extract was 11.79±0.76 μg/mL, while it was 10.16±0.29 μg/mL for BHA. In both disk diffusion and well diffusion methods, with the increase of the concentration of extract, the inhibition zone diameter increased. The ethanolic extract of lemon verbena at the concentration of 12.5 mg/mL had no inhibitory effect on gram-negative bacteria growth. In both methods, the extract had the greatest effect on S. aureus. The MIC of ethanolic extract ranged from 8 to 128 mg/mL, depending on the type of bacteria (gram-positive or gram-negative).

The ethanolic extract of lemon verbena has higher antimicrobial effects on gram-positive bacteria. Therefore, it can be used in food and pharmaceutical industries as a natural antimicrobial agent. Considering the increasing resistance of bacteria to chemical antibiotics, more studies on lemon verbena and its antibacterial compounds are needed for treating infections.