Effects of Harvesting time and Duration of Extraction on Essential oil Compositions of Origanum vulgare L.

In this research, samples of Origanum were collected in areas of Kojour region of northern Iran during the flowering stage on June 2008. The Sampling was conducted in three time intervals: morning, noon and evening. All samples were air-dried in the shade. Extraction carried out by hydro-distillation technique by modified clevenger trap for two different times (2 and 4 hours). Analysis was evaluated by GC and GC-MS apparatus. Based on dry weight of the herb, oil percentage of morning, noon and evening samples were 1.00, 1.11 and 1.01% after 2 hours and 0.92, 0.86 and 0.80% after 4 hours of distillation, respectively. It shows that morning samples have the most essential oil contents. Among 35 identified compounds of the essential oils of this herb, Thymol, γ- Terpinene, 1, 8-Cineole, ß-Cymene and Carvacrol were the major compounds in the first two hours of extraction while after 4 hours of extraction, trans- Caryophyllene, Germacrene D, Bicyclogermacrene and decane were the most important essential oils.