Glucuronoarabinoxylan from coconut palm gum exudate: Chemical structure and gastroprotective effect

A glucuronoarabinoxylan (CNAL) was extracted with 1% aq. KOH (25 °C) from Cocos nucifera gum exudate. It had a homogeneous profile on HPSEC-MALLS-RI (Mw 4.6 × 104 g/mol) and was composed of Fuc, Ara, Xyl, GlcpA (and 4-O-GlcpA) in a 7:28:62:3 molar ratio. Methylation data showed a branched structure with 39% of non-reducing end units, 3-O-substituted Araf (8%), 3,4-di-O- (15%), 2,4-di-O- (5%) and 2,3,4-tri-O-substituted Xylp units (17%). The anomeric region of CNAL 13C NMR spectrum contained 9 signals, indicating a complex structure. The main chain of CNAL was characterized by analysis of a Smith-degraded polysaccharide. Its 13C NMR spectrum showed 5 main signals at δ 101.6, δ 75.5, δ 73.9, δ 72.5, and δ 63.1 that were attributed to C-1, C-4, C-3, C-2 and C-5 of (1 → 4)-linked β-Xylp-main chain units, respectively. CNAL exhibited gastroprotective effect, by reducing gastric hemorrhagic lesions, when orally administered (1 and 3 mg/kg) to rats prior to ethanol administration.