Structure of an arabinogalactan from the edible tropical fruit tamarillo (Solanum betaceum) and its antinociceptive activity

Abstract

A structural characterization of polysaccharides obtained by aqueous extraction of ripe pulp of the edible exotic tropical fruit named tamarillo (Solanum betaceum) was carried out. After fractionation by freeze-thaw and α-amylase treatments, a fraction containing a mixture of highly-methoxylated homogalacturonan and of arabinogalactan was obtained. A degree of methylesterification (DE) of 71% and a degree of acetylation (DA) of 1.3% was determined by (1)H NMR spectroscopy and spectrophotometric quantification, respectively. A type I arabinogalactan was purified via Fehling precipitation and ultrafiltration through 50 kDa (cut-off) membrane. Its chemical structure was performed by sugar composition, HPSEC, methylation, carboxy-reduction and (13)C NMR spectroscopy analysis. Intraperitoneal administration of the arabinogalactan did not reduce the nociception induced by intraplantar injection of 2.5% formalin in mice, but significantly reduced the number of abdominal constrictions induced by 0.6% acetic acid, indicating that fraction has an antinociceptive effect on the visceral inflammatory pain model.

Keywords: Antinociceptive effect; Highly-methoxylated homogalacturonan; Solanum betaceum; Tamarillo; Type I Arabinogalactan.