The effect of methanol and ethanol foliar application on essential oil composition of peppermint

Mentha spp. are the main source of menthol essential oils. Medicinal plants sprayed with alcohols such as methanol and ethanol may cause vegetative growth and secondary metabolites improvement. The current study was carried out to evaluate ethanol and methanol foliar application efficiency on peppermint essential oils composition at Medicinal Plant Research Farm of Islamic Azad University, Miyaneh Branch based on randomized complete block design. One month aged peppermint plantlets were sprayed by 10, 20, 30 and 40% (v/v) ethanol and methanol aqueous solutions repeated twice two and four weeks after. The plants were harvested in flowering stage and their essential oils were extracted using hydro-distillation. The essential oils composition was specified using GC and GC-MS techniques. All phytochemicals in peppermint essential oils were significantly affected by hydroalcoholic solutions application but transpulegol, cis-pulegol, menthyl acetate, e-caryophyllene, α-himochalene and germacrene D. Plants sprayed by upper than 10% hydroalcohol solutions contained more menthol, significantly. Moreover, menthol amount was in higher values in the case of methanol application than ethanol. However, most of phytochemicals of peppermint were effectively promoted using ethanol 30%. Also, menthone and isomenthone negatively affected by methanol spraying in peppermint. Therefore, considering current research findings, methanol spraying is recommending to increase peppermint essence quality.