Structural features of pectic polysaccharides from the skin of Opuntia ficus-indica prickly pear fruits Original Research Article

After removal of the mucilage with water at room temperature, pectic polysaccharides were solubilized from Opuntia ficus-indica fruit skin, by sequential extraction with water at 60 °C (WSP) and EDTA solution at 60 °C (CSP). Polysaccharides with neutral sugar content of 0.48 and 0.36 mol/mol galacturonic acid residue were obtained, respectively, in the WSP and CSP extracts. These pectic polysaccharides were de-esterified and fractionated by anion-exchange chromatography, yielding for each extract five fractions, which were thereafter purified by size-exclusion chromatography. Two of these purified fractions were characterized by sugar analysis combined with methylation and reduction–methylation analysis. The study was then supported by 1H and 13C NMR spectroscopy. The results showed that the water-soluble fraction WSP3 and the EDTA soluble fraction CSP3, consisted of a disaccharide repeating unit →2)-α-l-Rhap-(1 → 4)-α-d-GalpA-(1→ backbone, with side chains attached to O-4 of the rhamnosyl residues. The side chains contained highly branched α-(1 → 5)-linked arabinan and short linear β-(1 → 4)-linked galactan.