Effect of different extraction techniques on the composition of essential oil isolated from fennel (Foeniculum vulgare Mill.) rhizome

The aim of the presented work was to compare the efficiency of innovative (solvent-free microwave extraction, microwave-assisted hydrodistillation and supercritical CO2 extraction) extraction techniques vs. conventional Clevenger hydrodistillation of essential oil (EO) from poorly studied fennel rhizome. It was found that innovative extraction techniques enhance the EOs/extracts isolation, save time and exclude solvents providing green ecologically technologies. Solvent-free microwave extraction proved to be the most efficient with limonene and (E)-anethole as dominant compounds in concentration of 12.34 +/- 0.31 and 35.63 +/- 1.51 mg/ml, respectively, as well as with the largest number of isolated and identified compounds. Primary aroma compounds were identified by two direct headspace techniques - static headspace extraction (HSS) and headspace solid phase microextraction (HS-SPME) confirming limonene and (E)-anethole as dominant compounds in primary aroma mixture with 53.7 +/- 2.02% and 30.9 +/- 1.43% (HSS) and 69.8 +/- 2.80% and 13.1 +/- 0.11% (HS-SPME), respectively.