Biotechnology for Pulp and Paper Processing by Pratima Bajpai

Author:Pratima Bajpai
Language: eng
Format: epub
Publisher: Springer Singapore, Singapore

15.2 Enzymes Used in the Production of Dissolving Pulp

Hemicellulose degrading enzymes mainly xylanases have been used for selective removal of pentosans in preparing dissolving-grade pulp . These enzymes are produced by many bacteria and fungi (Viikari et al. 1993, 1994). In the earlier studies (Viikari et al. 1986, 1987), crude culture filtrates of hemicellulases produced by different microorganisms were used and most of the reports published are based on results with unpurified enzymes. The culture filtrates used, however, contained xylanases as the main activity and the enzyme preparations were generally dosed according to the xylanase activity. Thus, when small doses were used, the amounts of other activities, mainly other hemicellulolytic and some cellulolytic enzymes were very low. Even with the unpurified enzymes, identification of the sugars released in the enzymatic treatments confirmed that xylanase was the major activity (Viikari et al. 1987, 1990). Some difference in the amount and composition of liberated sugars were observed when hemicellulase-rich culture filtrates (same xylanase dose) from different microorganisms were used (Viikari et al. 1994). The increase in reducing sugars can be influenced by the α-xylosidase activity in the enzyme preparation used, but it can reflect the presence of other hemicellulases or cellulase activities in the enzyme preparation used. The production of dissolving pulp requires the use of enzyme preparation that has little activity against amorphous cellulose . Cellulases have been considered to be detrimental to pulp treatments, if present in hemicellulase preparations (Viikari et al. 1994). This is especially true, when both endoglucanase and cellobiohydrolase are present in crude enzyme preparations. Due to the synergistic action of cellulolytic enzymes , a rapid depolymerization of cellulose occurs.

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