Pectic polysaccharide from immature onion stick (Allium cepa): Structural and immunological investigation

The structure of a water-soluble pectic polysaccharide (PS) isolated from immature onion stick (Allium cepa) was investigated using acid hydrolysis, methylation analysis, periodate oxidation study, and NMR studies (H-1, C-13, DQF-COSY, TOCSY, NOESY, ROESY, HSQC, and HMBC). The results of the above experiments indicated that the PS contained D-galactose, 6-O-Me-D-galactose, 3-O-acetyl-D-methyl galacturonate and D-methyl galacturonate in a molar ratio of nearly 1:1:1:1 and possesses a backbone of [-> 4)-alpha-D-GalpA6Me-(1 -> 4)-alpha-D-GalpA6Me-(1 -> ] in which one methyl galacturonate was substituted at O-3 position by an acetyl group and the neighboring methyl galacturonate being substituted at O-2 with a side chain, alpha-D-Galp-(1 -> 4)-6-O-Me-beta-D-Galp-(1 ->. The probable structure of repeating unit of the pectic polysaccharide was established as: [GRAPHICS] The pectic polysaccharide showed in vitro splenocyte, thymocyte as well as macrophage activations. (C) 2012 Elsevier Ltd. All rights reserved.