Hydrolysis of extracted and fibre-bound xylan with Aureobasidium pullulans enzymes

The enzymatic hydrolysis of arabinoxylan extracted from oat spelts and fibre-bound xylan present in dissolving pulp was investigated and compared using purified beta-xylanase and beta-xylosidase as well as the crude enzyme preparation of the yeast Aureobasidium pullulans. By means of size-exclusion and anion exchange chromatography both enzymes were purified to homogeneity with apparent molecular masses of 20 kDa (beta-xylanase) and 216 kDa (beta-xylosidase). Addition of greater activities of beta-xylosidase (up to 1.5 IU g(-1) of araboinoxylan) to beta-xylanase (1.5 IU g(-1) of araboinoxylan) in the enzyme-arabinoxylan reaction mixture resulted in the amount and rate of release of xylose and xylo-oligomers being increased. In the absence of beta-xylosidase only xylobiose, xylotriose and higher oligomers were detected by high performance liquid chromatography. When beta-xylanase or beta-xylosidase or a beta-xylanase/beta-xylosidase mixture was added to dissolving pulp, release of xylose and xylo-oligomers (xylobiose, xylotriose and higher oligomers) was observed in all instances using thin-layer chromatography. The results showed that the purified and crude enzymes of A. pullulans were only partially effective in the removal of xylan from dissolving pulp and the hydrolysis reaction was both time- and substrate-dependent. (C) 1997 Elsevier Science B.V.