Influence of storage conditions on the essential oil composition of Thymus daenensis Celak

The changes in the compositions of essential oils (EOs) from the aerial parts of Thymus daenensis were determined at different temperatures and storage times. The EOs of air-dried samples were obtained by hydrodistillation and analysed by gas chromatography (GC) and gas chromatography/mass spectrometry (GC/MS). Changes of EO compositions were detected during storage for 3 months in refrigerator (4 °C), freezer (−20 °C), and at room temperature. The results indicated that at room temperature, the proportions of compounds with lower boiling temperatures such as α-pinene (4.3-0.5%), α-terpinene (1.8-0.5%) and myrcene (1-0.4%) along with γ-terpinene (10.1-4.7%) and p-cymene (8.3-4.7%) as thymol and carvacrol precursors, were decreased. However, the amounts of thymol and carvacrol considerably increased by 26.6 and 23% after 3 months, respectively. Increasing of thymol and carvacrol by storage at room temperature represents an increase in the oil quality index. Furthermore, the oil compositions showed the least alterations and kept the primary quality when stored at low temperatures, particularly at −20 °C.