Extraction, purification and antioxidation of a polysaccharide from Fritillaria unibracteata var. wabuensis

Rich polysaccharides were directly observed in the bulbs of Fritillaria unibracteata var. wabuensis (FUW) using the periodic acid-Schiff (PAS) method and microexamination. An acidic water-soluble heteropolysaccharide (FWPS1-1) was isolated from FUW through ethanol precipitation, decoloration, deproteinization, dialysis and separation using a DE-52 anion-exchange column and a Sepharose G-150 gel filtration column. FWPS1-1 (average molecular weight: ~7.44 kDa) has many branches and long side chains; holds the triple-helix conformation; was composed of mannose (Man), galacturonic acid (GalA), galactose (Gal), xylose (Xyl) and arabinose (Ara) with a molar ratio of 2.62:5.59:10.00:0.76:9.38; and features side chains that may be composed of Ara, Man, Gal and GalA, while the backbone may be composed of Xyl, Ara and Gal. In addition, the backbone of FWPS1-1 mainly consists of α-type glycosidic bonds. Bioactivity tests in vitro showed that the polysaccharide exhibited weak 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity and low ferric reducing antioxidant power (FRAP) but high 2,2-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid)l (ABTS) radical scavenging activity, good Fe(II)-chelating ability and remarkable DNA damage protective activity. FWPS1-1 was the first heteropolysaccharide purified from FUW and showed good antioxidant activity and DNA protective effect. The results confirmed that macromolecule is also bioactive ingredient that requires attention like the small-molecule active compounds in FUW.