Essential oil composition of Norwegian peppermint (Mentha x piperita L.) and sachalinmint [Mentha sachalinensis (Briq.) Kudo]

Production of varieties of the medicinal plants Mentha X piperita (peppermint) and Mentha sachalinensis (sachalinmint) was investigated over a 2-year trial period (1995-1996) with regard to harvesting date, oil content and terpene composition. Oil accumulation of peppermint (clones "Hardanger" and "Toyen") and sachalinmint (var. "Mentolcsepp") increased throughout the season. Oil accumulation in both peppermint and sachalinmint was higher in plants grown in southern than in northern parts of Norway. An attempt was made to correlate the dependence of peppermint oil accumulation on the plant's age with the development of the peltate and capitate glands during the morphological development of the leaves. Changes in menthone-menthol metabolism were related to plant maturation for peppermint, with increasing menthol and reduced menthone content from the vegetative stage to full bloom. In contrast, the menthol-menthone content in sachalinmint was unchanged during plant maturation in 1995, while the results from 1996 showed increasing menthol content throughout the season.