The Effect of Different Drying Methods on Drying Kinetics, Mathematical Modeling, Quantity and Quality of Thyme Essential Oil

The drying process plays an important role in the treatment of medicinal plants, in order to maintain the quantity and quality of the essential oil extracted from the plant. Because Medicinal herbs containing essential oils If they are not dried immediately or their essence is not extracted, they will lose their active ingredients and volatile compounds.The aim of this study is design a hybrid dryer to drying medicinal plants and comparison their results with traditional drying methods (sun and shade).The effects of different drying methods (hybrid dryer, oven and shade drying) on the essential oil content and chemical composition of thyme were studied. The essential oils from each organ type were extracted by hydrodistillation and the chemical components were analyzed by GC/MS systems. Mathematical modeling results showed that the Midilli model can fit the drying curves with high accuracy. The highest essential oils yield of 2.4 % (v/w) was obtained by a hybrid dryer. Results indicated that hybrid dryer could keep the 24 Kinds of volatile compounds of Thymus while these values were 10 and 6 for oven and shadow methods, respectively. The main components of the essential oils in different drying methods were including alpha and beta pinene, caryophyllene, caryophyllene oxide, carotol, thymol, thymol methyl ether, terpinene-4-ol, gama-terpinene, p-cymene.In general, hybrid drying method is recommended as the best method for post-harvest thyme processing.