Softwood residues are the most abundant feedstock available for bioconversion in many northern countries. However, the high costs for delig-nification and enzymatic hydrolysis currently deter commercialization of softwood bioconversion processes. This study evaluates the abilities of two novel fungal preparations (MSUBCl and MSUBC2) and two commercial cellulase preparations (TRl and TR2) to hydrolyze cellulose in Douglas-fir pretreated by steam explosion or ethanol organosolv process. MSUBCI showed significantly better performance than the other preparations on both lignocellulosic substrates. In particular, MSUBCI achieved> 76% cellulose conversion for hydrolysis of steam-exploded Douglas-fir (~ 44% lignin) after 72 h at low enzyme loading (10 filter paper units/g of cellulose) and without B-glucosidase supplementation.

Seven cellulase preparations from Penicillium and Trichoderma spp. were evaluated for their ability to hydrolyze the cellulose fraction of hardwoods (yellow poplar and red maple) pretreated by organosolv extraction, as well as model cellulosic substrates such as filter paper. There was no significant correlation among hydrolytic performance on pretreated hardwood, based on glucose release, and filter paper activity. However, performance on pretreated hardwood showed significant correlations to the levels of endogenous β-glucosidase and xylanase activities in the cellulase preparation. Accordingly, differences in performance were reduced or eliminated following supplementation with a crude β-glucosidase preparation containing both activities. These results complement a previous investigation using softwoods pretreated by either organosolv extraction or steam explosion. Cellulase preparations that performed best on hardwood also showed superior performance on the softwood substrates.

Seven fungal cellulase preparations from Trichoderma and Penicillium spp. were evaluated for their ability to hydrolyze the cellulose component of lignocellulose samples prepared from softwoods by steam explosion or organosolv pretreatment. Hydrolysis was quantified using two indices: mean specific rate and specific conversion. The activities of the cellulase preparations on model cellulosic substrates (filter paper, carboxymethylcellulose and Avicel) were also determined, together with their β-glucosidase, xylanase, pectinase, galactomannanase and β-glucanase activities. The ability of a cellulase preparation to hydrolyze pretreated softwood showed little correlation with its activity on filter paper, carboxymethylcellulose and Avicel; however, there was a significant correlation with its level of endogenous β-glucosidase and xylanase activity. Differences in the performance of the various cellulase preparations were substantially reduced following supplementation with a commercial β-glucosidase preparation from Aspergillus niger. In addition to β-glucosidase, this preparation was shown to contain significant levels of endogenous xylanase activity. It appears that the levels of endogenous β-glucosidase and xylanase are important factors in determining the ability of a cellulase preparation to hydrolyze pretreated softwood and that deficiencies in the levels of both enzymes can be compensated by supplementation with corresponding activities present in the β-glucosidase preparation. Presumably, β-glucosidase improves cellulose hydrolysis by reducing end-product inhibition by cellobiose, while xylanase activity increases the accessibility of cellulose to cellulases.

Softwood residues are the most abundant feedstock available for bioconversion in many northern countries. However, the high costs for delignification and enzymatic hydrolysis currently deter commercialization of softwood bioconversion processes. This study evaluates the abilities of two novel fungal preparations (MSUBC1 and MSUBC2) and two commercial cellulase preparations (TR1 and TR2) to hydrolyze cellulose in Douglas-fir pretreated by steam explosion or ethanol organosolv process. MSUBC1 showed significantly better performance than the other preparations on both lignocellulosic substrates. In particular, MSUBC1 achieved >76% cellulose conversion for hydrolysis of steam-exploded Douglas-fir (∼44% lignin) after 72 h at low enzyme loading (10 filter paper units/g of cellulose) and without β-glucosidase supplementation.