Ultrasound- and microwave-assisted extraction of phenolic compounds from Satureja montana L. using lactic acid–urea natural deep eutectic solvent

The combination of green extraction techniques and natural deep eutectic solvents (NADES) represents a sustainable approach for the efficient recovery of bioactive compounds from phytochemical-rich plant materials. Therefore, this study aimed to chemically characterize green Satureja montana L. (Lamiaceae) herb extracts obtained by ultrasound-assisted extraction (UAE) and microwave-assisted extraction (MAE) in combination with a lactic acid–urea NADES (NADES_LA:U) system. Additionally, NADES_LA:U system was evaluated as a greener alternative to conventional solvents, together with the efficiency of UAE and MAE. UAE was performed for 30 min at 40 °C, 40 kHz, and 360 W, while MAE was carried out in three 5 s cycles at 180 W. Electrical energy consumption and CO₂ emissions were calculated based on the extraction parameters for each technique. A total of six extracts, three obtained by UAE and three by MAE, were prepared using NADES_LA:U, 70% ethanol, and water as extraction solvents. Rosmarinic acid, trans-cinnamic acid, rutin, quercetin, and naringenin were determined by High-Performance Liquid Chromatography (HPLC). For both green extraction techniques, the NADES_LA:U system was the most efficient solvent for extracting rosmarinic acid, trans-cinnamic acid, rutin, and quercetin. Naringenin contents showed minor variations across the investigated extracts. MAE provided comparable or improved extraction efficiency relative to UAE, while reducing both energy consumption and CO₂ emissions 240-fold. Therefore, the combination of NADES solvents and MAE offers a sustainable alternative to conventional extraction systems, enabling efficient recovery of phenolics, while reducing extraction time, energy consumption, and environmental burden. Future studies should focus on optimizing extraction conditions and assessing the potential application of these green S. montana extracts in the pharmaceutical, food, and cosmetic industries.