The bioactive compounds in burdock ( L.) roots, including chlorogenic acid (CGA) and cynarin, are valuable for use in nutraceutical foods. The ultrasound-assisted extraction of bioactive substances from dried burdock root powder (DBR) was investigated with 95% ethanol to reduce the impact of polysaccharide inulin on the extraction of free CGA and cynarin. The ethanolic extraction of CGA and cynarin was evaluated under ultrasound (300 W) at 40 kHz (U40) and 120 kHz (U120) with shaking at 120 rpm (S120) for comparison. Using a 1/30 (g/mL-solvent) solid-to-liquid ratio at 30 °C in 120 min, amounts of CGA and cynarin with U40 were as high as 818.74 μg/g-DBR and 173.68 μg/g-DBR, respectively, being much higher than those with U120 and S120. Total phenolic content, total flavonoid content, and antioxidant activity of the extract using U40 were significantly better than using U120 and S120. For U40 and U120, CGA increased with a decreasing solid-to-liquid ratio, while cynarin showed a decrease with a decreasing solid-to-liquid ratio using U120. Moreover, no observable degradations of free CGA and cynarin in ethanol were detected. By combining ultrasound and ethanol, the extracts with high-content CGA and cynarin from burdock roots were effectively achieved for use in health foods.
