Qualitative and Quantitative Changes in the Essential Oil of Origanum vulgare L. ssp. gracile as Affected by Different Harvesting Times

Qualitative and quantitative variations in the essential oil of wild growing Origanum vulgare L. ssp. gracile plants were studied in response to different phenological stages (pre, full and post-flowering). The essential oil of air-dried leaves was isolated by water distillation using a Clevenger-type apparatus and was analyzed by Gas Chromatography (GC) and Gas Chromatography–Mass Spectrometry (GC/MS). The highest (1.87%) and the lowest (1.01%) essential oil content were obtained from post-flowering and pre-flowering stages, respectively. In total, 24 components were identified and quantified in three phenological stages representing 96.75, 97.63, and 98.59% of the oil, respectively. Carvacrol (46.62, 46.5 and 27.6%), ρ-cymene (7.76, 13.54 and 37.08%) and γ-terpinene (21.54, 13.91 and 6.82%) were the main constituents of essential oils in pre, full, and post- flowering stages, respectively. Oxygenated monoterpenes (43.35-61.32%) and monoterpene hydrocarbons (30.81-48.02%) were the main classes of identified compounds in three essential oils. According to the findings of this research, the post-flowering stage can be considered as the most appropriate time for obtaining the highest essential oil content, but to achieve the highest rate of phenolic compounds, the pre-flowering and full-flowering stages can be recommended.