Ultrasound-assisted deep eutectic solvents extraction of bioactive natural products: a sustainable alternative to conventional extraction techniques.

Natural products derived from medicinal plants, including purified compounds and standardized extracts, remain important sources of drug leads due to their exceptional structural and chemical diversity. However, their efficient recovery is often limited by complex plant matrices, low target concentrations, and the thermal sensitivity of many bioactive constituents. Consequently, extraction strategies must achieve high recovery while preserving compound stability and biological functionality. Ultrasound-assisted extraction (UAE) has emerged as a promising green technology that enhances cell disruption and mass transfer through acoustic cavitation, thereby reducing extraction time, energy demand, and solvent consumption compared with conventional methods. In parallel, deep eutectic solvents (DES) and natural deep eutectic solvents (NADES) have attracted considerable attention as alternatives to traditional organic solvents because of their low volatility, compositional tunability, and high solubilization capacity. Their combination with ultrasound offers a synergistic platform in which cavitation accelerates matrix disintegration and molecular transport, while DES/NADES provide adaptable extraction environments for chemically diverse compounds. This review critically evaluates the use of DES/NADES for the recovery of alkaloids, anthocyanins, carotenoids, flavonoids, polyphenols, polysaccharides, terpenoids, and xanthones using UAE. It places particular emphasis on solvent design, extraction mechanisms, operating variables, biological activity, and reported extraction performance. This review also examines current limitations in viscosity, solvent recovery, toxicity assessment, standardization, scale-up, and regulatory acceptance. Future progress will depend on integrating solvent engineering, mechanistic modelling, process intensification, and sustainability assessment to enable industrial application in pharmaceutical, food, cosmetic, and nutraceutical production.