Efficiency of the optimized microwave assisted extractions on the yield, chemical composition and biological activities of Tunisian Rosmarinus officinalis L. essential oil

The present study was aimed to determine the optimal conditions of microwave assisted hydrodistillation (MAHD) and solvent free microwave extraction (SFME) in order to improve the quality of Tunisian Rosmarinus officinalis L. essential oil. The effectiveness of microwave assisted extraction was evaluated by determining the yield, chemical composition and biological activities of R. Officinalis L. essential oil and then compared them with traditional hydrodistillation (HD) and steam distillation (SD). Results of this study confirm that SFME can be used to improve the quality of Tunisian R. officinalis L. essential oil because it gave the best results: shorter extraction duration (35 min vs. 40 min for MAHD, 120 min for SD and 180 min for HD), better chemical composition (24 compounds vs, 19, 11 and 21 compounds were identified by GC-MS in extracts obtained through MAHD, SD and HD, respectively and mostly consisting of a-pinene (42.57-35.62%), eucalyptol (64.71-20.82%), camphor (14.47-20.4%), myrtenal (4.33-7.39%) and isobomeol (2.28-9.8%)), reduced cost, less energy consuming and increases acetylcholinesterase activity. The better antimicrobial activities were obtained and showed the same resistance for all essential oils against each of gram negative (Escherichia coli, S. thyphimurium and Klebsiella pneumonia) and gram positive (Staphylococcus aureus and S. epidermidis) bacteria. S. aureus was sensitive to SFME essential oil with minimal inhibitory concentration of 2 mg/mL and minimal bactericidal concentration of 4 mg/mL. Electron micrographs provided more proofs to confirm that microwave methods were quicker than conventional (C) 2017 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.