Variation in the essential oil content and composition of a Finnish oregano collection

Abstract

Fifteen oregano samples (Origanum vulgare L.) from eleven different locations in southern Finland plus one commercial Greek oregano (Origanum viride ssp. viride) were cultivated in Mikkeli, south-eastern Finland in 2008 and 2009. The plants were harvested at flowering time in August 2009, dried and stored in paper bags. The plant material was submitted to hydrodistillation in a Karlsruher-Stahl apparatus for two hours in order to isolate the oil and determine the oil content. The oil content varied from 0.2 to 0.8% in the Finnish oreganos and was 3.7% in the Greek oregano. The oils were analysed by GC-MS using an unpolar RTX-1 and a polar Stabilwax column (30m x 0.20mm i.d. Restek Corporation, CA, USA). The identification was based on retention indices and comparison with library spectra. Altogether 47 components were identified and the identified constituents represented 64.9–96.9% of the total oil. The dominant constituents were sabinene (up to 17%), γ-terpinene (up to 12%), β-caryophyllene (up to 20%), germacrene-D (up to 17%), caryophyllene oxide (up to 23%) and carvacrol (up to 85%). A cluster analysis of the essential oil compositions classsifed the oils into five groups: 1) β-caryophyllene/germacrene-D, 2) caryophyllene oxide, 3) carvacrol, 4) β-caryophyllene and 5) sabinene/germacrene-D type. Only the Greek oregano was a carvacrol type. Great variations in oregano oils of Mediterranean origin have been reported (1, 2), but not in oregano of Finnish origin.