Evaluation of Antibacterial Activity and Chemical Composition Determination of Essential Oil of Mentha aquatica Collected from north of Iran

Introduction: The importance of herbal and spice essential oils is that in addition to creating flavor in foods, their main active ingredient has antimicrobial effects, for this reason, consumers prefer herbal oils to chemicals. The Lamiaceae are a family of flowering plants commonly known as the mint family. Many members of this family are aromatic herbs and are widely used as spices in the food industry. Mentha (also known as mint) is a genus of plants in the family Lamiaceae . The species that makes up the genus Mentha are widely distributed and can be found in many environments. Most grow best in wet environments and moist soils. The genus Mentha consists of over 20-30 species that grow widely throughout the world. Members of this genus are one of the most important plants producing essential oils. There are many varieties of essential oils in different species (Zargari, 1995). Mentha aquatica L. that known in the northern regions of Iran locally called Ojji, is a commonly spice herb has used. This plant grows in aquatic places throughout Iran, especially in northern Iran. One of the main habitats of this plant in Iran is Mazandaran province in northern Iran (Getahun et al., 2008). Food poisoning caused by Escherichia coli and Staphylococcus aureus are known as the most important causes of food poisoning. This study was caried out to evaluate the chemical composition and antibacterial activity of essential oil of Mentha aquatica L. against S. aureus and E. coli
Material and methods: Plant of Ojji (Mentha aquatic) was obtained from from local market in Sari township located in Mazandaran Province in northern Iran and was approved by the botany laboratory of Islamic Azad University, Gorgan branch. The essential oil of herb leafs was extracted by hydrodistillation method and Clevenger apparatus. Gas chromatography–mass spectrometry (GC-MS) was used to identify essential oil chemical compounds. The gas chromatograph used was Agilent 6890 with a capillary column of 30 m in length and an internal diameter of 250 μm and a layer thickness of 0.25 μm HP-5MS. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of the essential oil of this plant oil were determined using micro-dilution broth method or turbidimetric assay. The Bacterial strains used in this study were two species of Escherichia coli PTCC 1338 and Staphylococcus aureus PTCC 1112. The bacteria were provided in lyophilized form from Biotechnology Institute in Iranian Research Organization for Sciences and Technology, Tehran. Different dilutions of essential oil in Mueller Hinton Broth were exposed with bacterial suspension of 5 ×105CFU/ml of each of the bacteria tested for 24 hours at 37 ° C. After this time the results were recorded as microbial turbidity of visible. The last dilution (lowest concentration) in which microbial turbidity was not observed, as the minimum inhibitory concentration (MIC) was considered. For the determination of MBC, from the tube that contained essential oil concentrations higher than the MIC were cultured onto the Nutrient agar medium. The MBC was defined as the lowest concentration that allowed no visible growth on the agar (Cockerill et al., 2012).
Results and discussion: The results of the gas chromatography analysis were determined 27 chemical compounds that formed more than 98% of the essential oil compounds. 3-Carene were the highest concentrations chemical compound of Mentha aquatica essential oil with 61.24%. Cineol, Limonen and Agarospirol were other known compounds of the essential oil of this plant that were measured in quantities of 9.4%, 6.81% and 4.78%, respectively. 3-Carene is a hydrocarbon monoterpene. Therefore, the antibacterial activity of the essential oil of Mentha aquatica can be attributed to the presence of hydrocarbon monoterpens. Identification of the chemical constituents of the essential oil of Mentha aquatica in different parts of the world indicates different reports of the presence of different compounds in this essential oil. Different findings may be due to intrinsic properties of essential oils such as pre-harvest factors such as variety, environmental conditions, ecological factors and differences in extraction methods. Although production of secondary metabolites in plants are made by genetic processes, they are affected by environmental factors. The results of antibacterial tests indicated that S. aureus was more sensitive than E. coli to the essential oil of this plant as MIC and MBC of essential oil of this herb on the S. aureus 1.56 and 1.56 mg/ml and on the E.coli was 3.12 and 6.25 mg/ml respectively. The cause of the lower sensitivity of gram-negative bacteria may be due to the presence of an outer membrane in gram-negative bacteria that restricts the release of hydrophobic components of the essential oil into the lipopolysaccharide layer. One of the important properties of the essential oils is their hydrophobic properties, which distribute them in lipid portions of the cell wall, altering and destroying their structure and increasing their permeability. As a result, much of the ions and other vital contents of the cell leak out, eventually leading to bacterial death. Concerning the antibacterial activity of the essential oils, it has been suggested that phenolic metabolites in plants such as Mentha aquatica are capable of releasing a hydrogen from the hydroxyl group present in their aromatic ring and causing the oxidation of free radicals in lipids and other cellular membrane biomolecules and its destruction and thus produce their antioxidant, antimicrobial and anti-inflammatory properties.
Conclusion: The antibacterial activity of essential oil of Mentha aquatica can be attributed to the presence hydrocarbon monoterpene compounds such as 3-Carene along with compounds such as Cineol, Limonen, Agarospirol, Eucalyptol and Menthone that leads the potential for its use as a natural preservative in food.