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Modification of the Carbohydrate Composition of Sulfite Pulp by Purified and Characterized β‐Xylanase and β‐Xylosidase of Aureobasidium pullulans
Author(s) -
Christov L. P.,
Myburgh J.,
O'Neill F. H.,
Van Tonder A.,
Prior B. A.
Publication year - 1999
Publication title -
biotechnology progress
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.572
H-Index - 129
eISSN - 1520-6033
pISSN - 8756-7938
DOI - 10.1021/bp9900054
Subject(s) - xylanase , xylobiose , xylose , hemicellulose , pulp (tooth) , chemistry , xylan , dissolving pulp , sulfite , biochemistry , hydrolysis , kappa number , food science , cellulose , enzyme , fermentation , kraft process , pulp and paper industry , medicine , pathology , kraft paper , engineering
Both β‐xylanase and β‐xylosidase were purified to homogeneity from a xylose‐grown culture of Aureobasidium pullulans. Cellular distribution studies of enzyme activities revealed that β‐xylanase was an extracellular enzyme, during both the exponential and stationary phases, whereas β‐xylosidase was mostly periplasmic associated. The β‐xylanase exhibited very high specificity for xylan extracted from Eucalyptus grandis dissolving pulp, whereas the β‐xylosidase was only active on p ‐nitrophenyl xyloside and xylobiose. Comparison of k cat / K m ratios showed that the β‐xylanase hydrolyzed xylan from dissolving pulp 1.3, 2.1, and 2.3 times more efficiently than Eucalyptus hemicellulose B, Eucalyptus hemicellulose A, and larchwood xylan, respectively. The β‐xylosidase exhibited a transxylosylation reaction during the hydrolysis of xylobiose. When applied on acid sulfite pulp, both enzymes released xylose and hydrolyzed xylan to a different extent. Although β‐xylosidase (0.4 U/g pulp) liberated more xylose from pulp than β‐xylanase (4.7 U/g pulp), it was responsible for only 3% of xylan solubilization. Treatment of pulp with β‐xylanase liberated 51.7 μg of xylose/g and hydrolyzed 10% of xylan. The two enzymes acted additively on pulp and removed 12% of pulp xylan. A synergistic effect in terms of release of xylose from pulp was observed when the enzyme mixture of β‐xylanase and β‐xylosidase was supplemented with β‐mannanase. However, this did not result in further enzymatic degradation of pulp xylan. Both β‐xylanase and β‐xylosidase altered the carbohydrate composition of sulfite pulp by increasing the relative cellulose content at the expense of reduced hemicellulose content of pulp.