Isolation, Purification, Structure Characterization and Antioxidant Activity of Alkali-extracted Polysaccharide from Abalone Viscera

Objective: Alkali-extracted polysaccharides from Abalone viscera (Aavp) were isolated and purified. The structure and antioxidant activity of Aavp were studied, which would provide a reference for developing and applying polysaccharides. Methods: The crude alkali-extracted polysaccharide was prepared by hot alkali extraction and alcohol precipitation. After the purification of DEAE sepharose fast flow and sephacryl S-400 HR, the purified polysaccharide was obtained and subjected to the structural analysis and antioxidant activity assay, such as Gas chromatography (GC), high-performance liquid chromatography (HPLC), infrared spectroscopy (IR), and thermogravimetric analyzer (TGA), etc. Result: Four kinds of components (Aavp Ia, Aavp Ib, Aavp IIa, and Aavp IIb) were obtained from the crude polysaccharide. Because of the highest yield, Aavp IIa was selected for further structural analysis. Aavp IIa was composed of xylose and galactose, with a relative molecular weight of 166513 Da. IR characterized the α-glycosidic bond configuration. The composition of Aavp IIa was possible as follows: The molar percentage of the galactose 1→4 glycosidic bond was 11.81%, the galactose 1→3 glycosidic bond was 34.14%, and the galactose 1→2 glycosidic bond was 10.14%. The molar percentage of the xylose 1→3 glycosidic bond was 33.85%, and the 1→2 and 1→4 glycosidic bond was 10.06%. Thermogravimetric analysis showed that Aavp IIa was broken and decomposed at 226.4~332.6 °C, and the thermal weight loss rate was 43.65%. Antioxidant experiments showed that Aavp IIa had a scavenging rate of 85.89% for superoxide anion radicals and 62.17% for DPPH radicals, respectively, presenting a certain antioxidant activity. Conclusion: Aavp is a heteropolysaccharide with specific antioxidant activity.