Growing conditions and postharvest management can affect the essential oil of Origanum vulgare L. ssp. hirtum (Link) Ietswaart

Origanum vulgare subsp. hirtum (Link) Ietswaart (Greek oregano) has been cultivated since ancient times thanks to its herbal and therapeutic properties. Currently, it is added in various commercial preparations thanks to its essential oil composition. This group of secondary compounds is affected in quantity and quality by biotic and abiotic factors during the cultivating phase and by the postharvest management. Thus, the aims of the work were to study: (1) how the growing conditions (soil full-light treatment; pot full-light treatment; pot 50%-shade treatment) can affect the essential oil content and the essential oil profile of Greek oregano branches at full-blossoming stage; and (2) how the postharvest management (distillation of the essential oil from fresh herbs, dehumidified herbs or oven-dried herbs) can affect the essential oil content and the essential oil profile of this species. The growing conditions significantly affected the biometrical parameters. The pot full-light treatment contained the highest dry matter percentage (36.5%) and the highest essential oil content, which was directly correlated to the former parameter (r=0.890**). The postharvest management did not affect the essential oil content. The growing condition significantly affected the characterizing γ-terpinene, cis-sabinene hydrate, 4-terpineol, α-terpinene, linalyl acetate, and β-bisabolene, while it did not affect carvacrol (mean value 15.8%), p-cymene (mean value 6.0%), or sabinene (mean value 3.9%). The postharvest management significantly affected carvacrol, cis-sabinene hydrate, 4-terpineol, p-cymene, α-terpinene, linalyl acetate, and β-bisabolene, while it did not affect γ-terpinene (mean value 14.7%). The response of some compounds to growing conditions led us to hypothesise an essential oil profile of the plants grown in pots at 50%-shade to be more of a vegetative stage type oil than the essential oil profile of the plants grown in soil, although all were at the blossoming stage. The analyses on the individual compounds indicated that, even though the essential oil content in oregano did not change with a change in postharvest management, biochemical changes occurred on the profile. These could be due to enzyme activity, dilution effect or temperature effect during the drying processes. The oven-drying process and the dehumidifying process changed the essential oil profile in a similar way compared to the essential oil profile distilled from fresh herbs. Thus, when it is not possible to extract the essential oil directly from fresh herbs, processors can dry the oregano according to the equipments they have available.