Structural studies of the pectic polysaccharide from fruits of Punica granatum

Abstract

The polysaccharide PG_O containing 76 % of uronic acids, was obtained from peels and membranes of Punica granatum fruits by extraction to the aqueous solution of (NH₄)₂C₂O₄. The chemical structure of PG_O was characterized by enzymatic and partial acid hydrolyses, Smith degradation and 1D/2D NMR spectroscopy. It has been found that PG_O consisted mainly of highly methyl-esterified and lowly acetylated pectin. Backbone of the macromolecule was represented by 1,4-α-D-GalpA, 1,4-α-D-GalpA(OMe), 1,4-α-D-GalpA(OAc). The branched region PG_O contained minor segments of partially acetylated rhamnogalacturonan-I (RG-I). RG-I side chains were comprised of highly branched 1,5-α-l-arabinan and segments of arabinogalactan type I. In addition to pectins, PG_O contained the glucuronoxylans and xyloglucans, indicating a close interaction of these polysaccharides with each other in the cell wall. It was concluded that P. granatum fruit could be a promising source of pectic polysaccharides.

Keywords: Arabinan; Arabinogalactan; NMR; Pectic polysaccharides; Punica granatum; Structure.