Effect of different drying techniques on qualitative and quantitative properties of Stachys Schtschegleevii essential oil

Stachys schtschegleevii is an endemic species of Iran. It is a valuable medicinal plant which is widely used in herbal medicines. To obtain high-quality essential oil from this plant, the type of the applied drying technique plays a key role. The current study was aimed to investigate the effects of different drying methods (shade, sunlight, oven 40°C, oven 60°C, and microwave) on yield and essential oil composition of S. Schtschegleevii. The results indicated that the highest essential oil yield was related to microwave drying technique. Furthermore, α-pinene, germacrene-D, bicyclogermacrene, β-eudesmol, and spathulenol were found to be the major compounds. Drying method significantly changed major compounds percentage, for instance, monoterpene hydrocarbonssuch as α-pinene, β-pinene, germacrene-D, and myrcene significantly decreased due to oven drying (60°C), microwave or sunlight drying techniques. Moreover, bicyclogermacrene and β-eudesmol percentage significantly decreased due to direct sunlight-drying method. Consequently, microwave drying technique was found to be the most efficient technique in order to achieve the highest oil yield and shortest drying time. Practical applications: Hedge nettle (Stachys schtschegleevii Sosn) belongs to Lamiaceae family and is known as an important medicinal plant due to its flavoring, therapeutic, and preservative properties. Aerial parts of the plant are used to extract essential oil and hence type of the applied drying technique plays a key role in obtaining high-quality essential oil. Therefore, the influences of different drying techniques on essential oil content of S. schtschegleevii were examined and overall, microwave drying technique was found to be the most efficient technique in order to obtain the highest oil yield and shortest drying time; however, some of the major compounds were decreased due to the employment of this technique.