STRUCTURAL-ANALYSIS OF ACETYLATED HEMICELLULOSE POLYSACCHARIDES FROM FIBER FLAX (LINUM-USITATISSIMUM L)

Hemicellulose polysaccharides were sequentially extracted from defatte d and depectinized flax bast fibres with Me(2)SO (20 degrees C), hot w ater (100 degrees C), aq 5% NaOH (20 degrees C), and aq 17.5% NaOH (20 degrees C). The ethanol-precipitated Me(2)SO extract was fractionated by size-exclusion chromatography, and the two main fractions (fractio n II and III), covering 85% of the total, were analyzed by HPLC for co nstituting monosaccharides and acetyl content, and by NMR spectroscopy (H-1, C-13 and 2D-heteronuclear proton detected multiple-bond coheren ce (HMBC)). Fraction II contained a linear beta-(1 --> 4)-linked xylan , O-acetylated on C-2 and C-3 with an acetylation degree of 0.5. Fract ion In: was enriched in Man and Glc residues. NMR spectral data gave e vidence for the presence of a linear beta-(1 --> 4)-linked glucomannan , O-acetylated on C-2 acid C-3 of Man with an acetylation degree of 0. 5 (based on Man). HPLC analysis and H-1 and C-13 NMR spectral data sho wed that the ethanol-precipitated hot-water extract consists of an O-a cetylated rhamnogalacturonan I (RG-I) type structure. HPLC analysis of neutral monosaccharides indicates that the alkaline extracts are comp osed of glucomannan, xylan, and RG-I, having similar structures as tho se found in the Me, SO and hot-water extracts. (C) 1996 Elsevier Scien ce Ltd.