Dual-cooled microwave extraction of Foeniculum vulgare essential oil and its chemical composition and antibacterial activity: Comparison with hydrodistillation and conventional microwave

Numerous studies indicate that the efficiency of microwave extraction, a popular method for extracting essential oil, needs to be improved. In this study, we used fennel (Foeniculum vulgare) as the focused species, extracted its essential oil using three methods, including traditional hydrodistillation (HD), single-cooled microwave extraction (SCME) and dual-cooled microwave extraction (DCME), and then tested the chemical composition and antibacterial activity of the essential oils. The optimum parameters of DCME were liquid-solid ratio 5.6 mL/g, extraction time 27 min and irradiation power 600 W. The yield of fennel essential oil raised to 1.172%. The composition of essential oils obtained by both SCME and DCME was obviously different from that obtained by HD, such as higher monoterpene hydrocarbons in SCME and higher oxygenated monoterpenes in DCME. Furthermore, Salmonella Typhimurium and Escherichia coli were the most sensitive to fennel essential oil, followed by Staphylococcus aureus and Listeria monocytogenes. The activity of essential oil from different methods against four bacteria strains was similar. Our founding revealed that the improved microwave extraction greatly raised the yield of fennel essential oil, retained its fragrance and antibacterial activity. Overall, this study provides a theoretical basis for the separation and application of essential oils from natural aromatic plants.