ISOLATION AND PARTIAL CHARACTERIZATION OF THE NON-CELLULOSIC POLYSACCHARIDES OF FLAX FIBER

The non-cellulosic polysaccharides of flax fibre cells were isolated using chemical extraction methods. Extraction of mature retted flax fibre with the calcium chelating agent trans-1,2-diaminocyclohexane-N,N,N',N'-tetraacetic acid (CDTA) removed polysaccharides enriched in galacturonic acid. These pectic polysaccharides were fractionated by their solubility in water into two fractions that differed in their neutral sugar content. Extraction of the fibre with aqueous 24% (w/v) potassium hydroxide produced the first hemicellulosic fraction (Hc1), which was enriched in xylose and, to a lesser extent, glucose- and galactose-containing polysaccharides. Digestion of aliquots of this fraction using the fungal carbohydrase mixture, Driselase, yielded xylobiose and isoprimeverose, which are characteristic limit digestion products of xylans and xyloglucans, respectively. Digestion of Hc1 with a crude cellulase preparation from Aspergillus niger yielded oligosaccharide products, one of which was similar to a characteristic nonasaccharide subunit of xyloglucan. Further extraction of the fibre residue with aqueous 18% (w/v) potassium hydroxide supplemented with 4% (w/v) of boric acid removed a second hemicellulosic fraction (Hc2), which was enriched in mannose-containing polysaccharides. Digestion of this fraction with a highly purified endo-(1 --> 4)-beta-D-mannanase converted 67% of the total polysaccharide into oligosaccharides within one hour. The beta-D-mannanase-derived oligosaccharides had a monosaccharide composition of mannose-glucose of 1.6:1.0. Analysis of the oligosaccharides by TLC and high-performance anion exchange chromatography revealed products characteristic of a glucomannan similar to those found in hardwoods. The presence of beta-linked D-glucose residues was confirmed by the removal of glucose from the beta-D-mannanase-derived oligosaccharides by a purified beta-D-glucosidase. A final extraction of the fibre with aqueous 90% Me2SO containing 4% (w/v) of boric acid removed a further pectic fraction (Hc3) enriched in neutral sugars. Preliminary analyses suggest that this fraction may contain a polysaccharide akin to rhamnogalacturonan I.