Structural studies of biologically active pectin-containing polysaccharides of pomegranate Punica granatum

The polysaccharide PGW was isolated from peels and membranes of fruits of pomegranate P. granatum by hot water extraction. The methods of ion exchange chromatography, partial acid hydrolysis, enzymatic hydrolysis and NMR spectroscopy were employed to establish the major elements of its structure. It was shown that this polysaccharide contained polymers with different structures, the main components among which were pectic polysaccharides, represented mainly by highly methyl-esterified and lowly acetylated 1,4-α-d-galactopyranosyluronan and a minor amount of partially 2-O- and/or 3-O-acetylated RG-I. The side carbohydrate chains of the branched region of RG-I were mainly represented by terminal, 5-O-, 3-O-, 2,5-di-O-, 3,5-di-O- and 2,3,5-tri-O-substituted α-l-Araf residues indicating the presence of branched 1,5-α-l-arabinan and minor regions of 1,4-β-d-galactan or arabinogalactan type I. The degree of methylation of the isolated pectins varied depending on the method of treatment. As a result, peels and membranes of pomegranate fruits can be recommended as a source of highly and lowly methyl-esterified pectic polysaccharides.