Structural characterization and antioxidant activity of alkali-extracted polysaccharides from quinoa

A polysaccharide component (SQAP-2) was isolated from quinoa by alkaline extraction and purified with DEAE-Sepharose Fast Flow and Sephacryl S-300 column chromatography. The chemical structure of the polysaccharide was characterized, and the impact on antioxidant activity was evaluated. Polysaccharide SQAP-2 (2.02 x 10(3) Da) is a type of glucose whose glycosidic bond Glc-(1 ->, -> 4)-Glcp-(1 ->, -> 4, 6)-Glcp-(1 -> linkages were identified through gas chromatography-mass spectrometry. Nuclear magnetic resonance confirmed the monosaccharide composition and glycosidic linkage content, and a suggestion of the structural formula was provided. Their radical scavenging capacity was evaluated, and scavenging activity against DPPH, ABTS, hydroxyl, superoxide radicals, and ferric reducing ability exhibited excellent radical scavenging activities of approximately 21.71 +/- 1.25%, 49.46 +/- 1.59%, 70.10 +/- 3.39%, 70.49 +/- 2.09%, 51.25 +/- 1.16%, respectively, at 3 mg/mL. The isolated quinoa polysaccharides could represent an antioxidant agent once the structural features and antioxidant activities are definitively characterized.