Structural studies of the pectic polysaccharide from fruits of Punica granatum
The polysaccharide PGO 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 PGO was characterized by enzymatic and partial acid hydrolyses, Smith degradation and 1D/2D NMR spectroscopy. It has been found that PGO 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 PGO 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, PGO 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.