Characterization and antioxidant activities of polysaccharides from Passiflora edulis Sims peel under different degradation methods

Water extracted polysaccharide from P. edulis peel (WPEP) was degraded using hydrochloric acid, ultrasonic-assisted hydrochloric acid, and α-amylase to obtained A-WPEP (acid hydrolysis WPEP), U-WPEP (ultrasonic-assisted acid hydrolysis WPEP), and M-WPEP (Enzymatic hydrolysis WPEP), respectively, and its relationship between structure and antioxidant activities was studied. Results showed that the solubility, internal crystalline, triple helical and surface structure of WPEP's degradation products was damaged to varying degree. Moreover, their antioxidant activities were lower compared with that of WPEP. The solubility of WPEP, A-WPEP, U-WPEP, and M-WPEP was 9.84, 6.78, 6.98, and 9.56 mg/mL, respectively. The IC50 values of their DPPH radical scavenging rates were 0.29, 1.34, 0.42 and 0.98 mg/mL, respectively. The complex formed by the degradation product with Congo red also showed different degrees of red shift in the alkaline solution. Enzymatic method had the least damage to the triple helical structure of WPEP compared with acid and ultrasonic-assisted acid method, and the better integrity of triple helical structure, the higher its antioxidant activities.