Tunable and Recyclable Natural Deep Eutectic Solvents for Efficient Extraction of Steviol Glycosides from Stevia rebaudiana.

Steviol glycosides (SGs), particularly rebaudioside A (RA) and stevioside (STV), are the primary natural sweeteners in Stevia rebaudiana and are increasingly utilized as zero-calorie sucrose substitutes. Although water is environmentally friendly, its poor selectivity limits efficient extraction of SGs, while conventional organic solvents raise environmental concerns. Auxiliary techniques such as ultrasound-assisted extraction often require high energy input or specialized equipment. Natural deep eutectic solvents (NADES) offer a sustainable, tunable alternative for SGs extraction. In this study, the Conductor-like Screen Model for Real Solvent (COSMO-RS) was applied to screen 403 DES combinations, revealing that NADES with strong hydrogen-bonding abilities significantly enhance SGs extraction. Experimental validation identified a betaine- propionic acid NADES (1:2 molar ratio) with 45 wt % water as optimal, achieving yields of 98.15 ± 2.62 mg/g RA, 59.83 ± 1.60 mg/g STV, and 7.16 ± 0.45 mg/g rebaudioside C (RC). To address challenges in SGs recovery from NADES, static adsorption/desorption experiments were conducted using AB-8 resin. Hydrophilic NADES were effectively recovered with deionized water washing and maintained over 85% extraction efficiency after two reuse cycles. Target SGs were efficiently desorbed with 70% ethanol, while impurities were removed with 30% ethanol. The resulting yields of RA, STV, and RC were 90.56%, 86.68%, and 65.89%, with corresponding purities of 53.23%, 29.06%, and 4.42%, respectively. These results demonstrate that the combination of the betaine-propionic acid NADES and AB-8 resin offers an effective and sustainable strategy for the extraction and purification of SGs from S. rebaudiana.