Solvent-free microwave extraction of essential oils from Thymus vulgaris L. and Melissa officinalis L.

The aim of this study was the comparison of essential oil of two herbs from lamiaceae family namely Thyme and Melissa via solvent-free microwave extraction (SFME) and hydrodistillation (HD). The process of SFME was optimized by central composite design (CCD) and response surface methodology (RSM). The essential oils were analyzed by gas chromatography-mass spectrometry (GC-MS). The compounds identified in higher relative abundance, for Thyme were, Thymol (HD: 28.92%, SFME: 32.17%), Carvacrol (HD: 26.18%, SFME: 29.25%), p-Cymene (HD: 13.25%, SFME: 9.51%) and γ-Terpinene (HD: 5.09%, SFME: 3.62%). In regard to Melissa oils, Caryophyllene oxide (HD: 23.71%, SFME: 24.95%), E-Citral (HD: 19.53%, SFME: 24.19%), Z-Citral (HD: 16.39%, SFME: 18.45%) and α-Muurolene (HD: 12.17%, SFME: 12.50%) were the most abundant compounds. The results showed that SFME was excellent in terms of saving energy and extraction time (42 min, compared to 4 h in HD). The research suggests that SFME is an outstanding alternative for extraction essential oils in industrial applications.