Green NADES-Based Pretreatment Combined with Microwave-Assisted Hydrodistillation for Enhanced Fennel Essential Oil...

Natural deep eutectic solvents (NADESs) are emerging green solvents widely applied to improve the extraction of essential oil (EO) through plant tissue pretreatment. Various NADESs, formulated from polyalcohols, sugars, and organic acids, were employed as pretreatment solvents prior to microwave-assisted hydrodistillation (MAHD) to facilitate plant cell wall breakdown and improve the efficiency of EO extraction. The findings revealed that the most effective pretreatment conditions for enhancing EO extraction involved using a NADES composed of choline chloride and glycerol (in a 1:2 molar ratio), applied to fennel seed powder at a solid-to-NADES ratio of 1:6 g/mL. Optimal performance was achieved with 20% water content in the NADES, microwave irradiation at 400 W for 6 min, followed by 96 min of MAHD. Under these conditions, the NADESs-based MAHD achieved the highest EO yield, increasing it from 1.33% with water-based MAHD to 2.70%. Fennel EO demonstrated the strongest antimicrobial activity against S. pyogenes and C. albicans., while the EO obtained from NADES-MAHD using Ch:Gly (1:2) showed the highest antioxidant activity, with 72.41% inhibition. Finally, GC-MS phytochemical analysis of the extracted EOs revealed anethole as the major compound. Notably, the application of NADES, particularly Ch:Gly (1:2), enhanced the relative content of monoterpene hydrocarbons. These findings highlight the superior effectiveness of deep eutectic solvents during the pretreatment stage in enhancing EO production.