Oligosaccharides obtained by enzymatic hydrolysis of birch kraft pulp xylan: Analysis by capillary zone electrophoresis and mass spectrometry

Neutral and acidic oligosaccharides were obtained from an unbleached birch kraft pulp by treatment with a Trichoderma reesei endoxylanase pI 9 and subsequently characterized using capillary zone electrophoresis (CZE) and matrix assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF-MS). The berate complexes of unsaturated acidic oligosaccharides having a 4-deoxy-beta-L-threo-hex-4-enopyranosyluronic acid (4 Delta UA) residue linked to a beta-D-(1 --> 4)-xylooligosaccharide backbone were separated by CZE and detected by their UV absorption at 232 nm without prior derivatization. Pre-column derivatization with the chromophore 6-aminoquinoline (6-AQ) followed by CZE in alkaline berate buffer using detection based on absorption at 245 nm was used in the case of neutral xylosaccharides. Furthermore, MALDI-TOF-MS was employed to determine the molecular masses of both unsaturated and saturated acidic oligosaccharides. The acidic oligosaccharides released upon endoxylanase treatment of the birch kraft pulp were a (4 Delta UA)-beta-D-xylotetraose, a (4 Delta UA)-beta-D-xylopentaose. a (4-O-methyl-alpha-D-glucurono)-beta-D-xylotetraose and a (4-O-methyl-alpha-D-glucurono)-beta-D-xylopentaose. Analysis after enzymatic hydrolysis with beta-xylosidase and a-glucuronidase from Trichoderma reesei strongly indicated that the uronic acid residue in these acidic oligosaccharides was linked to the D-xylose unit adjacent to the non-reducing D-xylose unit. The neutral xylosaccharides obtained after endoxylanase treatment of the pulp sample were D-xylose, beta-(1-4)-D-xylobiose and beta-(1-4)-D-xylotriose. (C) 1997 Elsevier Science Ltd.