Comparison of drying methods for the extraction of essential oil from dragonhead (Dracocephalum moldavica L., Lamiaceae)

In the present study, the effect of six different drying methods on the essential oil content and compositions of aerial parts of Iranian dragonhead was assessed. The highest and lowest essential oil contents (1.85 and 0.45%, respectively), were achieved in freeze-drying method and oven drying at 60°C, respectively. Essential oil analyses showed that the main constituents were geranyl acetate (56.5–33.2%), geranial (10.8–27.9%), neral (7.3–20.3%), and geraniol (6.7–13.5%). The highest percentages of geranyl acetate (56.5%) and geraniol (13.5%) were obtained with oven drying at 60°C. Cluster analysis of the essential oil constituents demonstrated three main groups based on drying methods. Freeze drying of aerial parts of dragonhead was the most suitable method allowing high-essential oil yields and short drying time. On the other hand, the highest level of marker compounds such as geranyl acetate and geraniol was obtained with oven drying at 60°C.