Ultrasound-assisted extraction of asiaticoside from Centella asiatica using betaine-based natural deep eutectic solvent

Centella asiatica is known for its valuable medicinal properties which highlight its potential application in the pharmaceutical industry. In this work, the ultrasound-assisted extraction (UAE) of asiaticoside from C. asiatica using betaine-based natural deep eutectic solvents (NADES) was developed for the first time. Eleven different NADES were screened to determine the best solvent to extract asiaticoside. Betaine-levulinic acid (Bet-Lev) at a molar ratio of 1:2 with water content of 30% (w/w) was selected as the most effective solvent. The influence of extraction time, temperature, ultrasound power, and liquid to solid (L/S) ratio were investigated in single-factor experiments. These parameters were optimized using response surface methodology (RSM) via the Box-Behnken design (BBD). The optimum conditions were 32 min extraction time, 36 °C extraction temperature, 140 W ultrasound power, and 49 mL/g L/S ratio to give an extraction yield of 229.92 ± 1.67 mg/g. A second order model was used to study the kinetics of asiaticoside extraction. Furthermore, the mechanisms involved in the extraction process were proposed and discussed. The morphology of C. asiatica powder was analysed before and after the extraction. A comparative study confirmed that the optimized UAE-NADES technique provided higher yield than that of the conventional extraction method.