Isolation and Characterization of Polysaccharides from Abaca Fiber

Abstract

Cellulose and xylan were found to be the major polysaccharide constituents in abaca fiber. Both hemicelluloses I and II were enriched in xylose, together with arabinose and glucose as the other major sugar constituents. These data implied that hemicelluloses I and II are probably composed of arabinoxylan, glucoxylan, and/or xylan, which corresponded with the studies by FT-IR spectroscopy. Arabinose and galactose were higher in all fractions of hemicelluloses I than in those of hemicelluloses II, whereas xylose and mannose were higher in all fractions of hemicelluloses II than in those of hemicelluloses I, suggesting that the dilute alkali pretreatments mainly solubilize the more branched hemicelluloses. The results obtained also suggested that dilute alkali pretreatments favored removal of small molecular chains of hemicelluloses I (Mw = 75 000−130 000) as compared to the hemicelluloses II, which had a higher degree of polymerization with molecular average weights between 123 000 and 227 000. Further studies showed that lignins, rich in syringyl units, are tightly associated with hemicelluloses in abaca fiber cell walls. Keywords: Abaca fiber; hemicelluloses; celluloses; lignin; alkali pretreatment; sugars; uronic acids; molecular weight; phenolic acids and aldehydes; FT-IR spectroscopy