Extraction and structural characteristics of pectic polysaccharides from Abies sibirica L

Structurally different pectins were isolated from the wood greenery of Abies sibirica L. by the sequential extraction with water (ASW), HCl solution (pH∼4) (ASA), and NH3 solution (pH∼8.5) (ASN). The GalA/Rha molar ratios for the ASW (15), ASA (8.9), and ASN (3.9) polysaccharides diminish in the order ASW > ASA > ASN, indicating a decrease in homogalacturonans and increase in rhamnogalacturonan I in this series. The ASWH, ASAH, and ASNH homogalacturonans derived by acid hydrolysis of ASW, ASA, and ASN have similar Mw 23.8, 21.1, and 18.9 kDa, respectively, corresponding to a mean polymerization degree of 97-122 for the GalA residue. The macromolecule backbone of ASN was represented mainly by moieties of partially methylesterified homogalacturonan and partially 2-O- and/or 3-O-acetylated rhamnogalacturonan I. The carbohydrate side chains of the branched region are primarily made up of terminal, 1,5-O-, 1,3,5-di-O- and 1,2,3,5-tri-O-substituted α-L-Araf residues and terminal, 1,3-O- and 1,3,6-di-O-substituted β-D-Galp residues. The currently known pectin models were refined.