Abstract: In the present study, the extraction of Undaria pinnatifida polysaccharides by ultrasonic treatment alone and in combination with cellulase hydrolysis was optimized by orthogonal array designs L16 (45) and L9 (34), respectively. The optimal ultrasonic-cellulase treatment conditions for simultaneously improved polysaccharide yield and scavenging activity of polysaccharide extracts against hydroxyl radicals generated in Fenton system were treatment time of 15 min, cellulase amount of 2.8 × 104 U/g algae power, treatment temperature of 70 ℃ and solid-to-liquid ratio of 1:80. Under the optimal extraction conditions, the extraction rate of Undaria pinnatifida polysaccharides was (4.522 ± 0.028)%. The hydroxyl radical scavenging rate of the obtained extract was up to (51.70 ±0.47)%. In addition, each of the four process conditions showed a significant effect on the extraction rate of Undaria pinnatifida polysaccharides (P＜0.01) and no significant effect on the scavenging activity of polysaccharide extracts against hydroxyl radicals (P＞0.05). The combination of ultrasonic and cellulase could significantly increase the extraction rate of Undaria pinnatifida polysaccharides and the scavenging activity of polysaccharide extracts against hydroxyl radicals as compared with ultrasonic alone (P＜0.01).

Key words: ultrasonic-enzymatic extraction, ultrasonic extraction, Undaria pinnatifida, polysaccharide, hydroxyl radical