Effect of drying methods on drying time, essential oil quantitative and qualitative of some of medicinal plants

Drying is one of the basic processes in post-harvest operation of medicinal plants that it affects their quantitative and qualitative characteristics. In order to study the drying time, percentage and content of most important component for some of the important medicinal plants such as Thymus vulgaris L., Matricaria chamomila, Melisa officinalis, Artemisia dracunculus and Mentha piperita , a laboratory experiment was conducted based on a completely randomized design with four replications at the Laboratory of Agricultural College, Ferdowsi University of Mashhad during year of 2012. Treatments were three temperatures by using oven (30, 40 and 60˚C), three powers by using microwave (100, 300 and 600w) and natural procedures (shaded and sunny areas). Drying process was continued until the moisture content of sample weight declined to 0.10 or 10% based on dry or fresh weights, respectively. The results showed that the effect of different drying methods was significant (p≤0.01) on drying time, essential oil content and amount of important component for these species. The highest drying time and essential oil content were observed in shaded area. Drying in shaded area enhanced amount of important component up to 100% compared to sunny area. By increasing in oven temperature and microwave power declined essential oil content and amount of important component for these species. It seems that increasing in drying rate and declining in input energy prevent from decreasing in essential oil yield, so low power of microwave is a suitable procedure for medicinal plant drying due to relatively rapid decrease in moisture content.