Ultrasonic-Assisted Natural Deep Eutectic Solvent Extraction of Proanthocyanidins from Lycium ruthenicum: Optimization, Kinetics, and Antioxidant Activity.

Proanthocyanidins, a new class of potent antioxidants, are recognized for their strong in vivo activity and occur in high abundance in Lycium ruthenicum. Although the extraction of these compounds from this plant has been extensively investigated, their inherent instability imposes stringent demands on the extraction process. Natural deep eutectic solvents (NADESs) have emerged as attractive alternatives for isolating bioactive constituents from plant materials thanks to their favorable biocompatibility, high extraction efficiency, and environmentally benign nature. Therefore, we have developed an efficient and green NADES-assisted ultrasonic extraction method for recovering proanthocyanidins from Lycium ruthenicum. Among the fourteen NADES formulations screened, the choline chloride-glycerol system (1:5 molar ratio, 30% v/v water) afforded the highest extraction yield. Single-factor experiments, combined with response surface methodology, led to the optimal conditions: solid-to-liquid ratio 1:15 g/mL, ultrasonic power 240 W, temperature 40 °C, and time 30 min. Under these conditions, the proanthocyanidin yield reached 12.19%, markedly outperforming that obtained with conventional methanol extraction. Kinetic analysis indicated that the extraction process conformed to the Logistic model, with coefficients of determination (R2) greater than 0.967 across the entire temperature range studied (20-50 °C). In vitro antioxidant assays further revealed that the extract exhibited significant concentration-dependent scavenging activities against •OH, DPPH•, and ABTS+• radicals. The IC50 values of proanthocyanidin extracts for •OH, DPPH•, and ABTS+• were 0.029 mg/mL, 0.56 μg/mL, and 0.011 mg/mL, respectively. Overall, these results establish a sustainable NADES-based protocol for the extraction of proanthocyanidins from Lycium ruthenicum, and underscore their promise as natural antioxidants for functional food and pharmaceutical uses.