Qualitative and quantitative variations of the essential oils of Dracocephalum kotschyi Boiss. as affected by different drying methods

Practical applications Using an appropriate drying method is the most important step in the postharvest processing of Dracocephalum kotschyi Boiss. to preserve its qualitative and quantitative essential oils. In this study, the effects of different drying techniques (sun, shade, conventional oven, vacuum oven, microwave, and infrared drying) were investigated on the essential oil content and composition of plants. Vacuum oven-drying at 40 degrees C was the best method for the retention of the essential oils of the samples. The essential oil was relatively sensitive to temperature, so its content was decreased with increase in the drying temperature. The results showed that oxygenated monoterpenes represented the main chemical class of essential oil components. Although the highest content of alpha-pinene and geranyl acetate (as major compounds) was obtained by conventional oven-drying at 40 degrees C, the highest content of limonene and alpha-terpineol was observed in the plants dried under the sun and by infrared drying at 0.5w/cm, respectively. The results suggest that vacuum oven-drying could be the best method for obtaining the highest content of essential oils from Dracocephalum kotschyi Boiss along with its major bioactive components. In addition, the microwave drying method was known as the most desirable drying method with regard to the final color of the dried products.