Linoj Kumar, Richard Chandra, and Jack Saddler. Forest Products Biotechnolgy/Bioenergy Research Group, University of British Columbia, Forest Sciences Centre, 2424, Main Mall, Vancouver, BC V6T 1Z4, Canada
Douglas-fir (Pseudotsuga menziesii) wood samples from six different trees and a Lodgepole pine (Pinus contorta) sample were steam pretreated at a single pretreatment condition (200oC 4% SO2 5 min) which had been previously shown to be effective in pretreating Spruce and Lodgepole pine wood to provide good overall sugar recovery and a cellulosic substrate that was amenable to subsequent cellulose hydrolysis. It was apparent that all of the softwoods were similar in terms of their responsiveness to steam pretreatment and subsequent enzymatic hydrolysis. The chemical composition of the pretreated substrates were all within a narrow range and the enzymatic hydrolysis yields from all of the pretreated softwood substrates at an enzyme loading of 20FPU/g of cellulose were greater than 60%. However, when the enzyme loading was reduced to 5 FPU, the hydrolysis yield from all substrates was greatly reduced. Applying a delignification step resulted in the almost complete hydrolysis of the cellulose component at both the 20 FPU (less than 12 h) and the 5 FPU (within 72h) enzyme loadings. Protein measurements indicated that ~50% of the total protein was still adsorbed on the solid fraction at the end of 72 hours despite the lack of any further, significant, increase in hydrolysis conversion. It was apparent that the lignin in the steam pretreated softwood acted both as a barrier and protein adsorbent, reducing the effective hydrolysis of the steam pretreated softwoods. The results suggest that, although steam pretreatment was effective in producing a softwood substrate with >90% glucose recovery, in order to obtain complete hydrolysis at reduced enzyme loadings, a delignification step will likely be required.
