The Utilization Of Autohydrolysis-Exploded Hardwood (Eucalyptus Regnans) And Sofiwood (Pinus Radiata) Sawdust For The Production Of Cellulolytic Enzymes And Fermentable Substrates

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Abstract
Softwood (Pinus radiata) and hardwood (Eucalyptus regnans) sawdust were pretreated by auto-hydrolysis at 200°C followed by explosive decompression. P. radiata pretreated pulps were poorly hydrolyzed by Trichoderma reesei C-30 cellulases compared to E. regnans pulps. Impregnation of P. radiata with 4.44% (w/w) SO2 followed by autohydrolysis explosion resulted in increased enzymic saccharification of the pulps. Sulfur dioxide treatment resulted in more of the hemicellulose components (heteroxylan and glucomannan) being removed during autohydrolysis than when P. radiata was pretreated by autohydrolysis alone. Trichoderma reesei C-30 cellulase digests containing 10% (w/v) of the pretreated pulps and 20 FPU units/g pulp resulted in cellulose-to-glucose conversion yields of 32% with E. regnans, 16% with P. radiata and 27% with SO2-treated P. radiata within 24 h at 50°C (pH 5.0) and could be increased to 74%, 27% and 48%, respectively, when the cellulase digests were supplemented with an exogenous β-glucosidase (Novozym 188). Cellulase, β-glucosidase and xylanase production by T. reesei C-30 grown in shake culture (25°C, pH 5.0) on 1% (w/v) of the pretreated pulps was highest when E. regnans and SO2-treated P. radiata were used as growth substrates, and enzyme yields compared with those when a purified α-cellulose (Solka floc) was used as growth substrate. Autohydrolysis-exploded P. radiata, however, proved to be a rather poor substrate for enzyme production. Typical FPU yields (as IU/g cellulose) were 53, P. radiata; 126, SO2-treated P. radiata; 136, Solka floc; and 165, E. regnans.