Steam Pretreatment of Douglas-Fir Wood Chips 693 Applied Biochemistry and Biotechnology Vol. 84–86, 2000 Copyright © 2000 by Humana Press Inc. All rights of any nature whatsoever reserved. 0273-2289/00/84–86/0693/$13.25 693 *Author to whom all correspondence and reprint requests should be addressed. Steam Pretreatment of Douglas-Fir Wood Chips Can Conditions for Optimum Hemicellulose Recovery Still Provide Adequate Access for Efficient Enzymatic Hydrolysis? ABDEL-LATIF BOUSSAID, ALI R. ESTEGHLALIAN, DAVID J. GREGG, KEUN HO LEE, AND JOHN N. SADDLER* Department of Wood Science, Chair of Forest Products Biotechnology, Forest Sciences Center, The University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada, E-mail: saddler@interchange.ubc.ca Abstract Douglas-fir sapwood and heartwood were impregnated with SO 2 and steam exploded at three severity levels, and the cellulose-rich, water- insoluble component was enzymatically hydrolyzed. The high-severity con- ditions resulted in near complete solubilization and some degradation of hemicelluloses and a significant improvement in the efficiency of enzymatic digestibility of the cellulose component. At lower severity, some of the hemi- cellulose remained unhydrolyzed, and the cellulose present in the pretreated solids was not readily hydrolyzed. The medium-severity pretreatment con- ditions proved to be a good compromise because they improved the enzy- matic hydrolyzability of the solids and resulted in the recovery of the majority of hemicellulose in a monomeric form within the water-soluble stream. Sap- wood-derived wood chips exhibited a higher susceptibility to both pretreat- ment and hydrolysis and, on steam explosion, formed smaller particles as compared to heartwood-derived wood chips. Index Entries: Douglas fir; sapwood; heartwood; steam explosion; enzymatic hydrolysis; fiber coarseness; particle size distribution. Introduction Bioconversion of lignocellulosic feedstocks to ethanol fuel holds prom- ise in providing a cleaner and more environmentally benign alternative to gasoline for the transportation sector. Various types of hardwoods and agricultural residues have been studied as potential feedstocks for ethanol fuel production (1–6), and extensive research has been conducted to