Optimization of Ultrasound‐Assisted Deep Eutectic Solvent Extraction and Bioactivities of Polysaccharide from Porphyra haitanensis

Abstract In this paper, ultrasound‐assisted method and deep eutectic solvent (DES) are used to extract polysaccharides from Porphyra haitanensis . The single‐factor experiment is carried out first, and then the response surface experiment is designed to obtain the optimal process conditions. The optimal extraction conditions are the molar ratio of choline chloride to oxalate of 1:1, the water content of DES of 60%, the solid–liquid ratio of 1:60 g mL −1 , the time of 120 min, the power of 200 W, and the temperature of 80 °C, with the extraction yield of 4.42%. And the yield of P. haitanensis polysaccharides (PHPs) is 3.14% and 3.31% by water immersion and ultrasonic water extraction, respectively, indicating that the DES extraction method is superior to these two methods, and the optimization effect is good. The extracted polysaccharides are tested for biological activity after separation and purification on DEAE and Sephadex G‐75 columns. The results of α‐glucosidase inhibitory activity and α‐amylase inhibitory activity show that PHPs have certain antioxidant activity. 1,1‐Diphenyl‐3‐nitrophenylhydrazine (DPPH) and 2,2‐diazo‐di‐3‐ethylbenzothiazolin‐6‐sulfonic acid (ABTS) free radical scavenging assays show that PHPs have certain antiglycemic activity.