Effect of pressure liquid Extraction and ultrasonic irradiation frequency on inulin, phenolic content and antioxidant activity in burdock (Arctium lappa L.) roots

Burdock (Arctium lappa L.) roots are traditionally used in folk medicine as diuretic and curing rheumatism, gastritis, gout, throat pain, arthritis and rashes. These pharmacological properties are due to many bioactive compounds such as flavonoids and fructooligosaccharides. Nowadays, the the application of “green” methods for extraction of natural compounds gains more and more attention. The object of the current research was to determine inulin and sugars content, phenolic content and antioxidant potential in 70% ethanol and water extracts obtained by two “green“ extraction methods, namely pressure-liquid extraction and ultrasound-assisted techniques. The content of total fructans, as well as inulin and sugars were analyzed by spectrophotometric resorcinol-thiourea method and high-performance liquid chromatography with refractive index detection. Total phenols and flavonoids were determined by Folin-Chiocalteu and Al(NO3)3 reagents. Antioxidant activity was evaluated by four reliable methods (DPPH, ABTS, FRAP, and CUPRAC). The established inulin content varied from 0.27 to 4.0 g/100 g DW in the prevalence of the ultrasound-assisted extract obtained with water. Additionally, the established phenolic compounds content (from 10.35 to 18.16 mg gallic acid equivalent (GAE)/g and antioxidant activities demonstrated the burdock roots as potential source phytonutrients with health beneficial properties.