Abstract:The sea cucumber Acaudina molpadioides is a low-value aquatic product of the ocean. To increase its value, in this study, dried body walls of low-value A. molpadioides were selected as research material, from which the polypeptides were extracted by employing twin-screw extrusion with sodium sulfite-assisted treatment. The extraction rate of polypeptides and free sulfhydryl groups, and protein solubility from extrudate of A. molpadioides were determined. Polypeptides were separated from the extrudate and purified with DA201-C type microporous adsorption resin, and the molecular weight distribution and antioxidant ability of the purified components were determined. The results showed that for the A. molpadioides treated with twin-screw extrusion-assisted 3.0% sodium sulfite, the polypeptide extraction rate, free sulfhydryl content, and protein solubility were (57.12±0.62)%, (110.32±0.07)%, and (28.72±0.13)%, respectively, which were significantly higher (P<0.05) by (7.66±0.35)%, (105.32±0.01)% and (4.91±0.15)%, respectively, compared with those of the control check (CK). Moreover, the molecular weights of the purified polypeptides component I and Ⅱ were 1000~3000 u and <1000 u, respectively. Additionally, comparing the A. molpadioides polypeptides with those in the CK group, twin-screw extrusion-assisted 3.0% sodium sulfite extraction group, purified component I, and purified component Ⅱ, the IC50 values of DPPH radical scavenging rate were 25.51 mg/mL, 12.72 mg/mL, 6.58 mg/mL, and 9.02 mg/mL, respectively, and the IC50 values of the superoxide anion radicals scavenging rate were 25.56 mg/mL, 13.51 mg/mL, 11.87 mg/mL and 8.44 mg/mL, respectively. The results of oxidation damage protection test suggested that for purified component I, the optimal concentration for the survival rate of LO2 cells was 80 μg/mL, with (20.33±0.41)% increase compared with that in the injured group; as for the purified component Ⅱ, it was 20 μg/mL with (17.07±1.18)% increase than that in the injured group. In summary, the twin-screw extrusion-assisted sodium sulfite treatment on A. molpadioides improved the extraction rate of polypeptide and the extracted polypeptide possessed enhanced antioxidant activity.
