Origanum glandulosum Desf. grown wild in Algeria: essential oil composition and glycosidic bound volatiles

The essential oils, isolated by distillation–extraction (DE) and hydrodistillation (H) for different extraction periods, from the aerial parts of Origanum glandulosum collected at the flowering phase in Algeria, were analysed by GC and GC-MS. The oil yields determined by hydrodistillation attained 1.8% (v/w) and 2.7% (v/w) when extracted for 10 min and 3 h, respectively. The essential oils were dominated by the monoterpene fraction (DE 95–96% and H 86–97%), carvacrol being the main component of all oils (49–57 and 45–47% for DE and H oils, respectively). The other main components (>5%) were γ-terpinene (DE 17–13 and H 18–13%), p-cymene (DE 14–10 and H 17–11%) and thymol (DE 7 and H 5–7%). The composition of the glycosidic bound volatiles showed very little resemblance to the corresponding essential oil fraction. Thirteen components were detected in the glycosidic bound volatiles, only six of which were also present in the essential oil. The oxygen-containing monoterpenes were the dominant fraction (75–97%) of the glycosidic bound volatiles, but the main component was dependent on the extraction period and not on the isolation procedure. Carvacrol (71% for DE and 61% for H) dominated the 10 min distillation, whereas thymoquinone, which was not present on the essential oil, was the dominant component in the 3 h distillation (79% for DE and 59% for H).