Study of essential oil extraction from Moroccan Rosmarinus officinalis L. by distillation based on quantum chemical calculation and molecular dynamics simulation

International audience In this work, essential oils were extracted from rosemary leaves (Rosmarinus officinalis L.) from the eastern region of Morocco using hydrodistillation (Hd) and steam distillation (Sd). The yield, chemical composition, thermal stability, and antioxidant activity of the essential oils obtained by the two methods were compared. Determining the chemical composition of rosemary essential oil, with GC-MS, showed a significant qualitative and quantitative difference in certain components. The Sd method improved the extraction of sesquiterpene compounds with high molecular weight and low vapour pressure. The findings reveal that sesquiterpene and oxygenated monoterpenes in essential oils improved the antioxidant activity and thermal stability. Determining antioxidant activity using DPPH and the β-carotene bleaching assay showed that the Sd and Hd oils presented good radical scavenging activity (IC50 = 4960 μg/mL for Hd oil and 4570 μg/mL for Sd oil), capable of delaying β-carotene discolouration with 16.3 and 9.71% inhibition for Sd and Hd respectively. Thermal stability analysis of the oil products was performed using TGA/DTG analysis, and the results showed that the decomposition points of Hd oil and Sd oil were 362 and 368 K respectively. Furthermore, to identify intermolecular interactions and develop better knowledge of phenomena occurring during the extraction of the family of sesquiterpene compounds by water, quantum chemical calculation and molecular simulation by molecular dynamics (MD) were performed. The results suggested the relative stability of caryophyllene-water and the development of intermolecular bonding interactions of van der Walls and steric effect, improving extraction of the substance studied under steam distillation conditions.