Effect of different drying methods on the essential oil content and composition of Anise hyssop (Agastache foeniculum [Pursh] Kuntze)

Anise hyssop (Agastache foeniculum [Pursh] Kuntze) is a medicinal and perennial herb, belonging to the Lamiaceae family. The essential oil of this plant is a rich source of Methyl Chavicol, giving antifungal and antibacterial properties to this plant. To evaluate the effect of different drying methods on the essential oil content and composition of Anise hyssop, the leaves were harvested at full flowering stage and dried by four methods (shade drying, sun drying, oven drying at 40, 60 and 80°C, and microwave oven drying at 180, 360, 540, 720, and 900W) in a completely randomized design with four replications. The drying process was continued until the moisture content of samples reached around 0.11 based on dry weight. Dried leaves were subjected to hydro-distillation using a Clevenger type apparatus to extract the essential oil. The oil samples were analyzed by GC and GC/MS. Results showed that drying methods had significant effect on the drying time and essential oil content. Minimum (4 minutes) and maximum (64 hours) drying time were obtained at 900 W microwave power and shade drying, respectively. The highest (1.51%) and the lowest (0.56%) essential oil content were observed in shade drying and microwave drying in 900 W, respectively. The results of essential oil analysis showed Methyl Chavicol was the main component of essential oil ranging from 83.1% (shade drying) to 94.6% (microwave drying at 720W). Overall, the findings of this study showed that shade drying in spite of long drying time was the best drying method. However, oven drying at 40°C or microwave method in low powers is recommended when our goal is fast drying and achieving essential oil with high percentage of methyl chavicol.