Study on gamma ray drying method and conditions and storage duration effects on essential oil and some physiological traits of Satureja spicigera (C. Koch) Boiss.

In this study, to investigate the effects of gamma ray to dry plant materials, conditions, and storage duration of the plants on the percentage and essential oil composition and some physiological traits of Satureja spicigera (C. Koch) Boiss., plant top shoots were collected at the flowering stage. Gamma ray irradiation was performed in the Atomic Energy Organization at five levels of 0, 2.5, 5, 7.5, and 10 kGy (kilo gray). Storage was carried out under two refrigerator (4°C) and room air temperature conditions at three storage duration levels of 0, 120, and 240 hours. The experiment was conducted as a factorial in a completely randomized design with three replications. Essential oil of flowering shoots was extracted by water distillation method and analyzed by GC and GC/MS quantitatively and qualitatively. According to the obtained results, gamma radiation affected the essential oil percentage and amount of p-cymene, thymol, carvacrol, phenols, flavonoids, and antioxidant activity significantly at the level of 1%. Storage duration had a significant effect on the essential oil percentage and amount of p-cymene, thymol, and carvacrol. Storage conditions showed a significant effect on the total phenols and flavonoids content and antioxidant activity of ethanol extract of S. spicigera. Means comparison of gamma radiation effects showed that the highest percentage of essential oil with 1.12% and 1.03% was obtained in the control and 5 kGy treatments, respectively. The highest amount of thymol (13.57%) and carvacrol (34.73%) was observed in the 10 kGy and control treatments, respectively. With 2.5 kGy gamma irradiation, the amount of phenolic compounds and antioxidant activity respectively increased by 1.4 and 1.76 times compared to the control. Of course, by keeping the plant in the refrigerator, the amount of thymol was reduced. The highest percentage of essential oil was related to the storage for 120 hours. The use of high intensity gamma radiation is suitable to achieve high thymol essential oil. The use of low radiation can also be useful for drying S. spicigera to obtain extracts containing more phenolic compounds. However, gamma radiation is not appropriate for plant materials drying to obtain essential oils of this species.