Ultrasound-assisted deep eutectic solvent extraction of flavonoids from Chinese bayberry leaves: Optimization, molecular mechanism, and antioxidant evaluation

An ultrasonic-assisted natural deep eutectic solvent (UAE-NaDES) method was developed to extract flavonoids from Chinese bayberry leaves. The extraction conditions were optimized by response surface methodology using a Box-Behnken design. The choline chloride and lactic acid (1:3, 20% water) NaDES exhibited superior flavonoid extraction efficiency (135.12 mg myricitrin equivalent/g dry weight) compared with 80% ethanol under optimized ultrasonication conditions (485 W, 25 min, 50 °C). Fifteen flavonoids were identified, among which myricitrin was the most abundant, followed by myricetin deoxyhexoside gallate and epigallocatechin gallate. Molecular dynamics simulations indicated that UAE-NaDES improved extraction efficiency by forming more stable hydrogen bonds and increasing the solvent-accessible surface area. Electron spin resonance spectroscopy confirmed that the extracts obtained by UAE-NaDES exhibited stronger DPPH and •OH radical-scavenging activities than those obtained using conventional organic solvent extracts. This study provides a sustainable and efficient green strategy for high-value utilization of Chinese bayberry leaves through flavonoid extraction.