The impact of the harvesting period and drying conditions on the essential oil yield of Rosmarinus officinalis, Thymus satureioides and Origanum compactum from the Taza-Taounate region

This study focuses on the influence of the harvesting period and drying conditions on the essential oil (EO) yield of three Moroccan aromatic plants; Rosmarinus officinalis, Thymus satureioides and Origanum compactum from the Taza-Taounate region. The plants studied were harvested, determinated and dried according to a detailed protocol carried out in the laboratory. The extraction of essential oils is carried out by hydrodistillation using a Clevenger-type system in order to determine and statistically compare the yield of each sample. The results showed that drying conditions significantly affect the EO yield of the three species. For Rosmarinus officinalis, the highest yield is obtained from aerial parts dried in the shade with 1.25 % for 1 to 3 days of drying and a temperature interval of 20 to 30 °C. In the same conditions, an optimal yield of 1.52% is obtained for Origanum compactum. For Thymus satureioides the maximum EO content is obtained after 3 to 5 days of drying in a temperature range of 15 to 25 °C. Out of these conditions, yields gradually decrease significantly to minimum yields at a 15-day drying period and a maximum temperature of 45 °C for all plants. The harvest period is also a crucial parameter in the improvement of the EO yield, the best EO levels were recorded during the period of March-August this period corresponds to the flowering stage of the three plants, which shows that the variation of the phenological stages is a key factor in the optimization of EO yields.