Antimicrobial and antioxidant activities of three Mentha species essential oils
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The present study describes the antimicrobial activity and free radical scavenging capacity (RSC) of essential oils from Mentha aquatica L., Mentha longifolia L., and Mentha piperita L. The chemical profile of each essential oil was determined by GC-MS and TLC. All essential oils exhibited very strong antibacterial activity, in particularly against Esherichia coli strains. The most powerful was M. piperita essential oil, especially towards multiresistant strain of Shigella sonei and Micrococcus flavus ATTC 10240. All tested oils showed significant fungistatic and fungicidal activity [expressed as minimal inhibitory concentration (MIC) and minimal fungicidal concentration (MFC) values, respectively], that were considerably higher than those of the commercial fungicide bifonazole. The essential oils of M. piperita and M. longifolia were found to be more active than the essential oil of M. aquatica. Especially low MIC (4 muL/mL) and MFC (4 muL/mL) were found with M. piperita oil against Trichophyton tonsurans and Candida albicans (both 8 muL/mL). The RSC was evaluated by measuring the scavenging activity of the essential oils on the 2,2-diphenyl-1-picrylhydrazyl (DPPH) and OH radicals. All examined essential oils were able to reduce DPPH radicals into the neutral DPPH-H form, and this activity was dose-dependent. However, only the M. piperita oil reduced DPPH to 50% (IC50 = 2.53 mug/mL). The M. piperita essential oil also exhibited the highest OH radical scavenging activity, reducing OH radical generation in the Fenton reaction by 24% (pure oil). According to GC-MS and TLC (dot-blot techniques), the most powerful scavenging compounds were monoterpene ketones (menthone and isomenthone) in the essential oils of M. longifolia and M. piperita and 1,8-cineole in the oil of M. aquatica.