ISOLATION AND CHARACTERIZATION OF POLYSACCHARIDES FROM ABACA FIBER

Cellulose and xylan were found to be the major polysaccharide constitu ents in abaca fiber. Both hemicelluloses I and II were enriched in xyl ose, together with arabinose and glucose as the other major sugar cons tituents. These data implied that hemicelluloses I and II are probably composed of arabinoxylan, glucoxylan, and/or xylan, which corresponde d with the studies by FT-IR spectroscopy. Arabinose and galactose were higher in all fractions of hemicelluloses I than in those of hemicell uloses II, whereas xylose and mannose were higher in all fractions of hemicelluloses II than in those of hemicelluloses I, suggesting that t he dilute alkali pretreatments mainly solubilize the more branched hem icelluloses. The results obtained also suggested that dilute alkali pr etreatments favored removal of small molecular chains of hemicellulose s I (M-w = 75000-130000) as compared to the hemicelluloses II, which h ad a higher degree of polymerization with molecular average weights be tween 123000 and 221000. Further studies showed that lignins, rich in syringyl units, are tightly associated with hemicelluloses in abaca fi ber cell walls.