STRUCTURAL FEATURES OF THE PECTIC POLYSACCHARIDES ISOLATED FROM RETTED HEMP BAST FIBERS

Pectic polysaccharides were solubilized from retted hemp bast fibre bu ndles, by sequential extraction with water and ammonium oxalate at 100 degrees C. The polysaccharides isolated from the extracts were de-est erified and fractionated by anion exchange chromatography, yielding fi ve fractions from boiling water extract and five fractions from oxalat e extract. Five of these fractions were characterized by chemicals met hods, H-1 and C-13 NMR, as polysaccharides containing galacturonic aci d, rhamnose and galactose units in variable ratios. Their chemical str ucture comprises a disaccharide repeating unit --> 2)-alpha-L-Rhap-(1 --> 4)-alpha-GalpA-(1 --> backbone, with short side chains attached to the rhamnosyl residues. The beta-D-Galactose residues are attached to O-4 of the rhamnosyl residues, but the amount of L-rhamnosyl residues that are 2,4-linked can vary from 36 to 75%, from one fraction to ano ther. A fraction corresponding to a mixture of oligosaccharides with a n average dp of 13, with ten galacturonic acid, two rhamnose and one g alactose units was also isolated. (C) 1996 Elsevier Science Ltd.