It has been postulated that plant essential oils can be used as natural preservatives to delay food spoilage, inhibit pathogen growth, and improve food quality. Lemon balm (Melissa officinalis, Lamiaceae) aerial parts and Moldavian dragonhead (Dracocephalum moldavica, Lamiaceae) aerial parts have antibacterial and antifungal activity. The purpose of this study was to evaluate the chemical composition, antimicrobial activity, and antioxidant capacity of lemon balm and Moldavian dragonhead essential oils with the goal of finding natural agents to protect against oxidation changes and pathogenic bacteria of food.
Lemon balm and Moldavian dragonhead aerial parts were collected at blossoming in the summer of 2013 in Urmia, Iran. The plants were confirmed by the Herbarium Department of Jahad Agriculture and Natural Resources Center of West Azerbaijan, Iran. Essential oils were extracted via hydro-distillation, and gas chromatography-mass spectrometry (GC-MS) was used to analyze the compounds in the essential oil. Antibacterial activity was evaluated via agar disk diffusion assay and micro-well dilution assay against Gram-negative bacteria Salmonella typhimurium and Escherichia coli, and Gram-positive bacteria Listeria monocytogenes and Staphylococcus aureus. Antioxidant activity was assessed with the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity (RSA) assay, β-carotene bleaching test (BCBT), and 2,2-azinobis 3-ethylbenzo thiazoline-6-sulfonic acid (ABTS) assay.
The lemon balm essential oil was found to contain 37 components, with the most prominent being citronellal (37.33%), thymol (11.96%), citral (10.10%) and β-caryophyllene (7.27%). Moldavian dragonhead essential oil was found to contain 22 components, with the most prominent being geranial (28.52%), neral (21.21%), geraniol (19.60%), and geranyl acetate (16.72%). The Gram-negative bacteria were more resistant than the Gram-positive bacteria against both essential oils. S. aureus was the most sensitive to both essential oils, and E. coli was the least sensitive. Accordingly, both essential oils had the lowest minimum inhibitory concentration (MIC) and minimum bactericidal concentration (BMC) against S. aureus and the highest against E. coli. A dose-dependent scavenging potency was demonstrated for both essential oils. Overall, lemon balm essential oil had better antimicrobial activity than Moldavian dragonhead, and both were potent antioxidants.
In this study, E. coli was not very sensitive to lemon balm essential oil. However, other studies report that E. coli are very sensitive to lemon balm essential oil. The difference between studies may be related to how essential oil composition varies depending on the climate, plant species, distillation conditions, and plant maturity at harvest. The authors conclude that lemon balm and Moldavian dragonhead may be effective natural preservatives in the food industry by inhibiting food-borne bacteria and protecting against oxidation changes. These findings need to be confirmed in a study where whole food is tested in lieu of Petri dishes and agar.
The authors do not state their competing interest.
Ehsani A, Alizadeh O, Hashemi M, Afshari A, Aminzare M. Phytochemical, antioxidant and antibacterial properties of Melissa officinalis and Dracocephalum moldavica essential oils. Vet Res Forum. 2017;8(3):223-229.