Effects of Drying Methods on the Essential Oil Content and Composition of Nepeta binaludensis Jamzad

Nepeta binaludensis Jamzad is an endemic and rare perennial plant belonging to the Lamiaceae family which grows in a limited area in Binaloud Mountain in northeast of Iran. In order to study the effect of drying methods on its essential oil content and composition, the aerial parts were collected in flowering stage from its habitat at altitude of 2650 m above sea level in July 2018. Seven drying methods as sun drying, shade drying, oven drying at 30oC, 40oC and 50oC and microwave drying (180W and 360W) were applied in three replications. The essential oils of all samples were obtained using a Clevenger type apparatus during 3 h. The essential oils were analyzed using gas chromatography (GC) and gas chromatography/mass spectrometry (GCMS). Data statistically analyzed using one way ANOVA (CRD) with three replications and mean comparison were made using the Tukey method. The highest oil yield was obtained in oven drying 50 °C (2.16%) followed by shade drying (1.96%). In contrast, the lowest values of essential oil content, 1.09 and 0.65%, were obtained in sun drying and microwave 360W, respectively. Twentyfour compounds were identified in the essential oils of N. binaludensis with various drying methods with neptalactone (23.154.0%), 1,8cineol (25.551.0%) and myrcene (2.04.0%) as major components. The highest percentage of 1,8cineole (51%) was obtained from sample dried in oven 50 °C, while, the highest amount of neptalactone (54.0%) was obtained from sample dried by the microwave 180 W. The results demonstrated that drying the aerial parts of N. binaludensis in the shade and oven 50oC are the best optimal methods to obtain the highest oil yield, while drying in microwave at 180 W is recommended to enhance higher neptalactone content in the oil.