Drying Effect on Yields and Chemical Composition of Essential Oils Extracted from the Moroccan Mentha spicata (L.) Aerial Parts

Spearmint (Mentha spicata L.) is one of the most used species in Morocco. The whole herb and essential oil are used in flavoring tea and also have medicinal, cosmetic and industrial importance. In this study, the influence of drying on essential oil (EO) yields and chemical composition of spearmint was assessed. The spearmint aerial parts were harvested at flowering stage from two regions of Middle-Atlas: Meknes (Latitude: 33°53’42; Longitude: 5°33’17"; Altitude: 522 m) and Azrou (Latitude: 33°25’59"; Longitude: 5°13’01"; Altitude: 1278 m) and subjected to shadow drying method. The oils were extracted by hydrodistillation from dry leaves and flowers of the herb then analyzed using GC/MS. The obtained essential oil yield increased from 2.4 % to 4.48 % and 1.54 % to 3.8 %, respectively for M. spicata L. from Azrou and that from Meknes during six days of drying. The main compounds were carvone ranged from 47.30 % to 67.14 % and from 64.97 % to 69.19 %, limonene from 4.48 % to 9.03 % and 6.33 % to 15.43 %, then trans-4-caranone about 2.84 % to 4.63 % and 0.82 % to 2.08 % respectively for Azrou and Meknes spearmint. The high concentration of these compounds was observed on the fifth day for M. spicata from Azrou while for that from Meknes: the carvone rate reached its maximum on the 2nd day and limonene on the 3rd day. Moreover, some compounds appeared during of drying process as menthone and pulegone. So, the drying in shade process of spearmint can be suitable and recommended for high-oil yield and active components.