Assessment of drying process, quantity of essential oil and mathematical modeling of lemon verbena (Lippia citriodora H. B. et K.) using hot air

Lemon verbena (Lippia citriodora H. B. et K.) is one of the medicinal plants, belonging to the family Verbenaceae. This plant has active ingredients with sedative, anticonvulsant, heartbeat away, anti-diarrhea and antimicrobial effects. Accurate drying of medicinal plants is inevitable in order to reduce the humidity and increase the longevity and quantity and quality of the active ingredients. In this research, hot air dryer was used to dry the leaves of lemon verbena by using temperatures of 30, 40 and 50ºC and different air speeds of 0.5, 1 and 1.5 m/s to reach a humidity of 15%. Essential oil was extracted by Clevenger apparatus. Results showed that effects of temperature and air speed and their interaction on drying time were significant. Results of mean comparisons showed no significant difference between the temperatures of 40ºC and 50ºC. With increase of temperature, the effect of air speed was negligible. The best treatment in terms of minimum drying time was 40ºC and 1 m/s speed. Different levels of temperature showed significant effect on quantity of the essential oil as the highest and the lowest essential oil level were respectively obtained at 30ºC and 40ºC. The speed of the hot air also showed a significant effect on quantity of the essential oil as the maximum essential oil was obtained at the speed of 0.5 m/s. The results of interaction effects showed that maximum essential oil obtained at 500C temperature and 0.5 m/s speed. Finally, 7 Mathematical models of thin layer drying for different conditions such as R2, SSE and RMSE were compared. According to the results, Modified Page was identified as the best model for drying lemon verbena.