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

• A substituted galacturonan was extracted from edible starfruit (Averrhoa carambola).
• It has a (1→4)-α-d-Galp A main chain branched at O-2.
• (1→5)-α-L-Araf and terminal α-L-Araf and α-d-Galp A units were found as side chains.
• It demonstrated antinociceptive and anti-inflammatory properties on formalin test.

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 α-d-Galp A units branched at O-2 by (1→5)-linked α-l-Araf and terminal α-l-Araf and α-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.