Ultrasound-Assisted Green Natural Deep Eutectic Solvent Extraction of Flavonoids from Wild Blueberry: Process Optimization, Composition Identification, and Antioxidant Activity

To improve the deep processing and utilization of wild blueberries, this study presents a green and highly efficient method for extracting flavonoids from blueberries. The approach combines natural deep eutectic solvents (NADESs) with ultrasound-assisted extraction. Among the 22 tested NADES, Betaine/urea (BU), was the most effective solvent for extracting flavonoids from blueberries. The extraction parameters of ultrasound-assisted betaine/urea (UABU) were optimized using a response surface methodology (RSM). This optimization procedure yielded the optimized conditions outlined below: a molar ratio of urea to betaine of 3.3:1, a water content of 60% (<i>m</i>/<i>v</i>), an ultrasonic power of 330 W, a solid-to-liquid ratio of 1:30, an extraction temperature of 50 °C, and an ultrasonic extraction duration of 30 min. Under these conditions, the total flavonoid content (TFC) extracted using UABU reached 6.06 ± 0.024 mg_RE/g_DW, a 1.44-fold increase compared to ultrasound-assisted 70% (<i>v</i>/<i>v</i>) ethanol (UAE). Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS) nontargeted metabolomics analysis revealed that the flavonoids extracted by UABU had highly relative content (RC) of Oenin, 3'-methoxy-4',5,7-trihydroxyflavonol, Isorhamnetin-3-O-glucoside and Isoquercitrin. Significant disparities exist regarding the types and RC of flavonoids obtained via UAE. Results from in vitro antioxidant assays demonstrated that UABU has superior antioxidant activity relative to UAE. This study demonstrated the feasibility of using NADESs, specifically BU, as an efficient and eco-friendly extraction medium for flavonoids from wild blueberries. The yield of flavonoids was increased by this method, and bioactive compounds were also protected-findings that underscore the potential of green solvents for application in the food industry.