Fractionation and characterization of polysaccharides from abaca fibre

Abaca fibre polysaccharides were fractionated into water soluble, pectic, 1 % NaOH soluble, hemicellulosic and cellulose fractions by extraction with h ot water, dilute hydrochloric acid (pH 1.6), aqueous 1% NaOH and 17.5% NaOH , respectively. Cellulose (60.4-63.6%) and hemicelluloses (20.8%) were the major polysaccharides in abaca fibres. The hot water soluble polysaccharide s contained noticeable amounts of pectic substances and a large proportion of neutral polysaccharides. The pectic polysaccharide preparation was enric hed in both galacturonic acid and neutral sugars, including xylose, glucose , galactose, arabinose, and rhamnose. Extraction of the fibre with aqueous 1% NaOH produced the hemicellulose-lignin complex, which was enriched in xy lose and, to a lesser extent, glucose-, arabinose- and galactose-containing polysaccharides, together with 7.6% associated lignin. Further extraction of the delignified fibre residue with aqueous 17.5%. NaOH removed the hemic ellulose fractions, which were strongly enriched in xylose-containing polys accharides. Besides ferulic and p-coumaric acids, six other phenolic monome rs were also detected in the mixtures of alkaline nitrobenzene oxidation of associated lignin in all the polysaccharide fractions. The content of boun d lignin in water soluble, pectic, and 1% NaOH soluble polysaccharides (Fra ctions 1, 2, and 3), isolated directly from the lignified fibres, was 12 ti mes that of the hemicellulosic preparations (Fractions 4 and 5) isolated fr om the delignified fibre residues. (C) 1998 Elsevier Science Ltd. All right s reserved.