Substituted galacturonan from starfruit: Chemical structure and antinociceptive and anti-inflammatory effects

Starfruit (Averrhoa carambola L) is an edible tropical fruit, which is usually consumed as a fresh table fruit or as fruit juice. It also exhibits various pharmacological activities. In this study, polysaccharides were extracted with boiling water and purified by freeze-thawing and Fehling treatments. After purification steps, a homogenous fraction was obtained. It was analyzed by sugar composition, gel permeation chromatography, methylation, and two-dimensional nuclear magnetic resonance (2D NMR) spectroscopy analyses. It comprised arabinose (Ara), galactose (Gal), and galacturonic acid (GalA) in a molar ratio of 12.3:1.7:86.0. Methylation and NMR spectroscopy analyses showed that it contained a substituted galacturonan composed of (1 -> 4)-linked alpha-D-Galp A units branched at O-2 by (1 -> 5)-linked alpha-l-Araf and terminal alpha-l-Araf and alpha-D-Galp A units. The effect of PFSCW (10-300 mg/kg, i.p.) on nocifensive behavior induced by intraplantar injection of formalin in mice was evaluated. The fraction demonstrated antinociceptive and anti-inflammatory properties, suggesting that it may be useful in therapeutic intervention for the management of inflammatory pain. (C) 2015 Published by Elsevier B.V.