XYLANASE-RESISTANT XYLAN IN UNBLEACHED KRAFT PULP

A water-soluble chromophoric xylanase-resitant xylan fraction (LF-D) w as separated from a hardwood unbleached kraft pulp (UKP) after hydroly sis with a cellulase/ xylanase-membrane bioreactor. LF-D contained ove r 70% unremovable inorganic atoms including Si, Na, and S, together wi th a beta-1,4-inked xylan. A nucleus exchange reaction and a nitrobenz ene oxidation showed that LF-D contained a trace amount of a lignin co mponent abundant in quinoid structures which had been partly demethyla ted during the course of kraft pulping. On the other hand, a higher mo lecular weight residual lignin fraction (HF-P), which was obtained fro m an impermeable part of the enzymatic digests, was found to have a di phenylmethane structure. LF-D was partially decolorized by Coriolus ve rsicolor and bacterial microflora without action of extracellular lign in peroxidase, Mn-peroxidase, laccase or xylanase.