Ultrasound-Assisted Extraction of Flavonoids from Erythrina crista-galli Twigs Using Natural Deep Eutectic Solvents: Process Optimization and Antioxidant Evaluation

Abstract

Natural Deep Eutectic Solvents (NADES) have emerged as promising, environmentally friendly alternatives to conventional organic solvents for the extraction of bioactive compounds. However, their application to Erythrina crista-galli, a species known for its rich flavonoid content and therapeutic potential, has not yet been systematically investigated. This study addresses this research gap by developing an ultrasound-assisted extraction (UAE) process using NADES, statistically optimized through Central Composite Design (CCD). Among thirteen NADES formulations tested, the NADES11 formulation, composed of lactic acid, citric acid, and glycerol in a molar ratio of 4.5:4.5:1, demonstrated the highest total flavonoid content (TFC) and was selected for further optimization using Response Surface Methodology (RSM). The optimal extraction conditions were established at 97 min, 64 °C, and a solvent-to-material ratio of 1:25. Under these optimized parameters, the antioxidant activities of NADES11 and ethanol extracts were evaluated using DPPH, ABTS, and FRAP assays. The NADES11 extract exhibited significantly higher antioxidant activities, with values of 0.3690 ± 0.0039, 0.2965 ± 0.0118 mmol Trolox/g, and 0.6095 ± 0.0059 mmol Fe²⁺/g, respectively, compared to the ethanol extract, which yielded 0.0532 ± 0.0022, 0.0439 ± 0.0009 mmol Trolox/g, and 0.1043 ± 0.0018 mmol Fe²⁺/g. These results confirm the superior capability of NADES11 not only in efficiently extracting flavonoid compounds but also in preserving their antioxidant properties.