Deep Eutectic Solvent-Based Ultrasound-Assisted Extraction of Flavonoids from Houttuynia cordata

Recently, deep eutectic solvents (DESs) have attracted much attention in the extraction and separation field because of their green characteristics, and they are widely used to extract various bioactive substances from plants. In this study, ten choline chloride (ChCl)-based mixtures were selected for extracting flavonoids from Houttuynia cordata. Then, the optimal conditions for the DES-based extraction of Houttuynia cordata flavonoids (HCFs) were determined through one-way experiments and response surface optimization (RSM). The optimal conditions were a 60 min extraction time, an extraction temperature of 40 °C, a water content of 30%, a solid-liquid ratio of 1:22 g·mL^-1, a molar ratio of 1:2, and an ultrasound power of 420 W. The antioxidant capacities of HCFs in terms of ABTS radical, DPPH radical, and hydroxyl radical scavenging capacity and nitrite inhibition capacity were determined. DESs can be efficiently recycled after extraction. This study developed an effective and environmentally friendly method for HCF extraction, thereby also supporting the development and utilization of natural products.