The key-aroma constituents of oregano (Origanum) grown wild in Greece unraveled by headspace GC-MS and Raman spectroscopy

Abstract

In the present work we utilized two techniques, Gas Chromatography – Mass Spectrometry (GC-MS) and Raman spectroscopy, to decode the aroma constituents of different Origanum (oregano) plants grown wild in Greece. Aerial parts of flowering Origanum plants were collected from three localities of the Greek mainland (Mt. Belles, Mt. Pelion and Kassandra Peninsula) and one in the SE Greek Archipelago (island of Kos). Their taxonomic identification suggests that plants of the mainland, with a spike-like inflorescence and actinomorphic calyces, belong to two subspecies of Origanum vulgare, viz. subsp. vulgare (Belles) and subsp. hirtum (Pelion and Kassandra). Plants from the island of Kos, having a corymbose inflorescence and 1-lipped calyces, belong to the species Origanum onites. Essential oils were extracted from the plants using a Clevenger apparatus. The static headspace GC-MS method resulted in the identification of many terpenes. Raman spectroscopy was carried out using a laser at 785.0 nm to minimize fluorescence. Results indicated that O. vulgare subsp. vulgare contained the most terpenes among the samples; O. onites consists mainly of carvacrol, whereas O. vulgare subsp. hirtum of either carvacrol or thymol. A comparison of the GC-MS and Raman spectroscopic methods was further performed.