GC/MS evaluation of thyme ( Thymus vulgaris L.) oil composition and variations during the vegetative cycle

• Published in: Journal of pharmaceutical and biomedical analysis 2002-07, Vol.29 (4), p.691-700
• Main Authors: Hudaib, Mohammad, Speroni, Ester, Di Pietra, Anna Maria, Cavrini, Vanni
• Format: Article
• Language: English
• Subjects: Analysis; Biological and medical sciences; Essential oil composition; Gas Chromatography-Mass Spectrometry; GC/MS analysis; General pharmacology; Medical sciences; Pharmacognosy. Homeopathy. Health food; Pharmacology. Drug treatments; Plant Oils - chemistry; Plant Stems - chemistry; Polar and non-polar capillary column; Retention (Kovats) index; Seasonal variations; Thymus Plant - chemistry; Thymus Plant - growth & development; Thymus vulgaris; Vegetative cycle
• ISSN: 0731-7085; 1873-264X
• DOI: 10.1016/S0731-7085(02)00119-X

Capillary GC/MS analysis based on polar and non-polar columns has been applied to evaluation of the volatile oils hydrodistilled from thyme ( Thymus vulgaris L.) plants. The adopted methodology has been used to monitor seasonal variations in the composition of the oil obtained from thyme herbs harvested at different periods during the plant vegetative and life cycles. Oils from thyme plants of young (2 years) and old (5 years) cultivations have been evaluated from four and two collections, respectively, effected throughout May/December growth period. Generally, the oil was found to be rich in the active monoterpene phenols (thymol and carvacrol) and their corresponding monoterpene hydrocarbon (HC) precursors ( p-cymene and γ-terpinene), which collectively showed synchronized patterns of variation during the different collection periods and in different seasons. The oil from old plant collected in May/June period (0.15% v/w) was characterized by significantly lower levels of monoterpene HCs (mainly γ-terpinene) and the highest levels of the oxygenated monoterpenes (linalool and borneol), monoterpene phenols (mainly thymol) and their derivatives (mainly carvacrol methyl ether), sesquiterpenes (mainly β-caryophyllene) and their oxygenated derivatives (e.g. caryophyllene oxide) in comparison with all other samples. A characteristic presence of camphor and thymodihydroquinone was also observed in the old plant oils. On the other hand, the young plant, collected in June/July just before the end of the vegetative cycle, provided the best oil yield (1.2%) with also the highest % content of the monoterpene phenols (thymol: 51.2% and carvacrol: 4%). This latter growth period can represent the best harvest time of young thyme plants in order to obtain an essential oil with better quality and quantity.