Structural and antioxidant studies of a new arabinoxylan from green stem Andrographis paniculata (Kalmegh)

A water soluble arabinoxylan (APPS), with a molecular weight ∼1.49 × 105 Da was isolated from the green stem of Andrographis paniculata. The APPS contained D-xylose, 2-methoxy D-xylose and L- arabinose in molar ratio of 3:1:1. The structure of the repeating unit in the polysaccharide was determined through several chemical (acid hydrolysis, Methylation analysis and periodate oxidation) and spectroscopic analysis (1D/2D NMR experiments) as: In vitro antioxidant assay, APPS was found to possess ferrous ion chelating activity (EC50 = 283 μg/ml), superoxide radical scavenging activity (EC50 = 470 μg/ml), and hydroxide radical scavenging activity (EC50 = 193 μg/ml). Thus, APPS could be used as a natural antioxidant agent for food and pharmaceutical industries.