Steam pretreatment of Douglas-fir wood chips - Can conditions for optimum hemicellulose recovery still provide adequate access for efficient enzymatic hydrolysis?

Douglas-fir sapwood and heartwood were impregnated with SO2 and steam explo ded at three severity levels, and the cellulose-rich, water-insoluble compo nent was enzymatically hydrolyzed. The high-severity conditions 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 hemicellulose remained unhydrolyzed, and the cellulose present in the pretreated solids was not r eadily hydrolyzed. The medium-severity pretreatment conditions proved to be a good compromise because they improved the enzymatic hydrolyzability of t he solids and resulted in the recovery of the majority of hemicellulose in a monomeric form within the water-soluble stream. Sapwood-derived wood chip s exhibited a higher susceptibility to both pretreatment and hydrolysis and , on steam explosion, formed smaller particles as compared to heartwood-der ived wood chips.