Diurnal Variation Effects in Essential Oils of Wild Thyme (Thymbra spicata var. spicata L.) Under Cultivation Conditions

Abstract

There are many folkloric uses of Thymbra spicata var. spicata. Very few thyme species are found in semi-arid climatic conditions. T. spicata is one among these which is not under cultivation anywhere. The essential oil of plant possesses high antibacterial and antioxidant properties due to presence of large amounts of phenolic components. The aim of this study was to verify the variation of essential oil and its composition among 12 different populations harvested every three hours in a day (from 06:00 to 21:00 h) along 24 hours for Thymbra spicata var. spicata on May 30, 2013. The essential oil of samples were analysed by GC-MS/FID. The results, proved that essential oil content of T. spicata var. spicata harvested at different times varied and ranged 2.02 to 5.04% such that the amount of essential oil content increased around noon (reaching its maximum at 12:00 h) followed by a decrease in afternoon hours. The essential oil of T. spicata var. spicata was analysed and a total of 20 components representing 89.57-99.14% of the oils were identified. The highest carvacrol content (70.87%) was obtained from 6.00 h harvest and the lowest one was obtained at 12.00 h harvest as 66.36%. Diurnal variation in p-cymene content was observed with maximum at 21:00 h harvest (6.89%) and minimum at 09:00 h (5.02%) harvest. γ-Terpinene content of essential oil was maximum when the plants were harvested at 12:00 h, while the lowest content was found when harvested at 06:00 h. Carvacrol content was highest in the morning harvest. The results suggest that high oil yield and carvacrol content vary according to the temperature and can be optimised by considering the harvest time of the plant during a day.