Production of cellulase enzymes and hydrolysis of steam-exploded wood.
Steam-exploded aspen has been examined as a candidate feedstock for both cellulose production and enzymatic hydrolysis of wood. Batch and fed-batch cultivation methods were evaluated and compared with previous experiments using ball-milled, crystalline cellulose (Solka Floe). Batch cultivation of Trichoderma reesei Rut C-30 on 9 wt% water-washed aspen yielded enzyme productivities and activities comparable to those obtained on Solka Floe (40 FP IU/L-h; 7. 5 FP IU/mL). Fed-batch cultivation of Rut C-30 resulted in higher enzyme productivities and tilers than batch cultivation (50 FP IU/L-h; 15 FP IU/mL). However, the overall enzyme production performance was lower than on Solka Floe at comparable cellulose feeding rates and concentrations. This may be due to the accumulation of steam explosion by-products and lignin in the fermentor.The hydrolysis of water-washed steam-exploded aspen was performed at different enzyme loadings and wood concentrations. Glucose production, using 10 and 15 wt% suspension, showed that while glucose concentration increased with wood load, the yield of glucose derived from cellulose decreased. With 10 wt% suspensions, it was possible to obtain a cellulose conversion to glucose above 95%. Low cellulose levels in the hydrolyzates indicated that the filter paper activity ratios (approximately 1.5), a significant result since the fungus was grown exclusively on wood. mIt also suggested that the observed yield decrease is more likely to be caused by glucose than cellobiose inhibition of the enzymes.
Lawrence Berkeley Laboratory and Department of Chemical Engineering, University of California, Berkeley, California 94720, USA.
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San Martin
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Blanch
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Wilke
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Sciamanna