Abstract: The structural characteristics and antioxidant activity of sea cucumber gonadal polysaccharide (SCGP) by ultrasound-assisted enzymatic hydrolysis (named SCGP-UAE) were evaluated in comparison with those prepared by enzyme-assisted extraction (named SCGP-E) and ultrasound-assisted extraction (named SCGP-U). The results showed that the total sugar content of the SCGP-UAE sample (69.13%) was significantly higher than that of the SCGP-E sample (58.76%) and the SCGP-U sample (62.93%) (P < 0.05). The ultraviolet and Fourier transform infrared (FTIR) spectra of the three polysaccharides showed similar characteristic absorption peaks. The results of Congo red experiment, scanning electron microscopy and thermal stability measurement showed that none of the polysaccharide samples contained a three-stranded helix structure, despite all showing an apparent lamellar structure and having good thermal stability. At 4 mg/mL concentration, the 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) cation radical and superoxide anion radical-scavenging activity and Fe2+-chelating ability of SCGP-UAE were 5.59%, 14.05% and 26.63% higher than those of SCGP-U, and 2.16%, 33.59% and 47.10% higher than those of SCGP-E, respectively. In summary, the ultrasound-assisted enzymatic hydrolysis method could extract polysaccharides with good antioxidant activity from sea cucumber gonad in high yield and thus have great application potential.

Key words: ultrasound-assisted enzymatic hydrolysis; sea cucumber gonad; polysaccharide; structural characteristics; antioxidant activities