| Abstract: | Autohydrolysis explosion pretreatment of hardwood (Eucalyptus regnans) sawdust at 200°C and 6.9 MPa gas pressure (steam + nitrogen) for 5 min solubilized 85% of the total hemicellulose components and produced a pulp that was highly accessible to attack by cellulases from Trichoderma reesei C-30 and by a commercial preparation, Meicelase. The autohydrolysis liquor, representing 15% of the original weight of the sawdust on a solids basis, consisted mainly of xylose, xylose oligomers and minor amounts of galactose, mannose, arabinose, glucose and uronic acids. Enzymic hydrolysis of pretreated E. regnans pulps using Trichodermal cellulases resulted in saccharification yields of <50% within 24 h from 10% (w/v) substrate slurries and 20 cellulase (FPU) units per g of pretreated pulp. The cellulose-to-glucose conversions were lower and this was attributable to the production of a compound(s) during enzymic hydrolysis that was inhibitory to the β-glucosidase component, but not the cellulases, in the Trichodermal cellulase preparations. Enzymic digests supplemented with Novozym 188 β-glucosidase showed >70% cellulose-to-glucose conversion within 24 h under similar conditions of hydrolysis. The inhibitor compound was not inhibitory to the Novozym 188 β-glucosidases. Alkali-extracted autohydrolysis-exploded pulps were less susceptible to hydrolysis than unextracted pulps. Factors that influenced the extent of cellulose conversion into glucose such as enzyme-substrate and cellulase-to-β-glucosidase ratios are also discussed. |
