Isolation, purification, structural characteristic and antioxidative property of polysaccharides from A. cepa L. var. agrogatum Don

Allium cepa L. var. agrogatum Don (ALAP) is commonly consumed in China as well as other regions and has various beneficial health effects. A novel acidic polysaccharide (named ALAP-21) was obtained from ALAP by ultrasonic and microwave-assisted extraction and purification using DEAE-52 anion exchange and Sephadex G-100 columns. The monosaccharide composition, structural and antioxidative properties of ALAP-21 were investigated by GC–MS chromatography, FT-IR and NMR spectroscopies and three antioxidative activity tests in vitro. The results showed that ALAP-21 was a heteropolysaccharide composed of glucose, galacturonic acid, mannose, galactose, arabinose, rhamnose, xylose, fructose and glucuronic acid with a relative molar ratio of 26.282: 27.546: 11.400: 4.781: 2.467: 2.445: 3.622: 1.106: 1.753, owning (1→4)-α-d-Glcp, (1→4)-α-d-GalAp6Me3OA, (1→4)-β-d-Galp6OMe, (1→2)-α-l-Rhap, (1→4)-β-d-Manp glycosidic linkages. (1→4)-α-d-Glcp and (1→4)-α-d-GalAp6Me3OA residues might be the main components of the sugar chain backbone of ALAP-21. Furthermore, ALAP-21 exhibited high potential for DPPH radicals (82.02%), hydroxyl radicals (53.33%) and superoxide anion radicals (50.28%). These results provide a reference for further research and rational development of ALAP polysaccharides. Keywords: Polysaccharides, Allium cepa L. var. agrogatum Don, Structural characterization, Antioxidative property