Ultrasound-assisted deep eutectic solvent extraction of total flavonoids from Houttuynia cordata Thunb. and their in vitro activity

This study optimized ultrasound-assisted deep eutectic solvent (DES) extraction of total flavonoids from Houttuynia cordata Thunb. and evaluated their in vitro antioxidant and antibacterial activities. Among eight screened DESs, choline chloride–lactic acid (1:1, 30% water) was selected as the optimal solvent. Using single-factor experiments and Box–Behnken response surface methodology (R 2 = 0.9942), the optimal extraction conditions were determined as a solid–liquid ratio of 1:30 g/mL, ultrasonic power of 360 W, temperature of 40 °C, and time of 50 min, yielding a maximum extraction yield of 4.67%. The extract exhibited concentration-dependent scavenging activity against DPPH, hydroxyl, ABTS⁺, superoxide anion, and nitrite radicals. Furthermore, it demonstrated potent antibacterial effects against Staphylococcus aureus subsp. aureus (MIC = 0.0187 g/mL, inhibition zone = 21.76 mm) and Escherichia coli (MIC = 0.0375 g/mL, inhibition zone = 18.03 mm). These findings confirm that the optimized DES-based extraction process is efficient and that the H. cordata flavonoid extract possesses significant antioxidant and antibacterial potential.