CHROMOPHORE RELEASE FROM KRAFT PULP BY PURIFIED STREPTOMYCES-ROSEISCLEROTICUS XYLANASES

Treating kraft pulps with the crude xylanase from Streptomyces roseisc leroticus followed by alkali extraction reduces the kappa number in a linear manner with enzyme doses up to about 3 IU/gm of oven-dry pulp. The enzyme complex consists of four isoenzymes designated Xyl1, Xyl2, Xyl3 and Xyl4. Each can release chromophores when used alone and each can facilitate alkali extraction to reduce the kappa number, but their relative abilities are different. Of the four isozymes, Xyl4 releases the least color and 237-nm-absorbing material whereas Xy]3 releases t he most. Xyl4 best enhances the ability of alkali to reduce the kappa number. The UV absorption spectrum of the material released by alkali extraction differs significantly from the spectral characteristics of that released during enzyme treatment. The alkali-solubilized material has a maximum absorptivity at 265 nm and relatively little absorptivi ty at 237 nm. The material released during enzyme treatment absorbs st rongly at 205 and 237 nm. UV/VIS spectroscopy of the enzyme- or alkali -released material does not show a characteristic lignin peak at 280 n m, nor does it reveal any notable peaks in the visible region. Analysi s of the material released by enzyme treatment revealed more than 40 p roduct peaks after fractionation by reversed-phase HPLC. We observed m any products with strong UV absorption. These were relatively hydrophi lic. Fewer products absorbed in the visible region. These were more hy drophobic. All four isoenzymes exhibit endo-action patterns; none form s xylose from oat-spelt xylan. The action patterns fell into two group s: endo-1 enzymes (Xyl1 and Xyl3) formed xylotriose (X3) and other low er oligosaccharides as the predominant products; endo-2 enzymes (Xyl2 and Xyl4) formed roughly equimolar amounts of X3, xylotetraose (X4), a nd xylopentaose (X5), and tended to leave larger amounts of undigested higher oligosaccharides.