HYDROLYSIS OF EXTRACTED AND FIBER-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 com pared using purified beta-xylanase and beta-xylosidase as well as the crude enzyme preparation of the yeast Aureobasidium pullulans. By mean s of size-exclusion and anion exchange chromatography both enzymes wer e purified to homogeneity with apparent molecular masses of 20 kDa (be ta-xylanase) and 216 kDa (beta-xylosidase). Addition of greater activi ties 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 re action mixture resulted in the amount and rate of release of xylose an d xylo-oligomers being increased. In the absence of beta-xylosidase on ly xylobiose, xylotriose and higher oligomers were detected by high pe rformance liquid chromatography. When beta-xylanase or beta-xylosidase or a beta-xylanase/beta-xylosidase mixture was added to dissolving pu lp, release of xylose and xylo-oligomers (xylobiose, xylotriose and hi gher oligomers) was observed in all instances using thin-layer chromat ography. The results showed that the purified and crude enzymes of A. pullulans were only partially effective in the removal of xylan from d issolving pulp and the hydrolysis reaction was both time- and substrat e-dependent. (C) 1997 Elsevier Science B.V.