Abstract

This study is focused on the effect of the application of biological pretreatment of Eucalyptus globulus Labill wood pieces on the cellulose digestibility by depolymerizing enzymes. Wood chips were incubated with five different white-rot fungi (WRF) for 30, 45 and 60 days at 25°C. The effect of the fungal action was determined as weight losses, changes in chemical composition and released sugars in the wood chips. Enzymatic hydrolysis was conducted in a discontinuous reactor at 37°C, using a commercial cellulase preparation from Trichoderma reesei. The enzyme/substrate ratio was 0.04 g/g. The highest weight losses were obtained using Stereum hirsutum and Lentinus edodes for all the incubation times, reaching 27.2% and 25.8% at 60 days, respectively. The lowest weight losses were produced by Coriolus versicolor and Pleurotus ostreatus, reaching 6.0 and 9.1%, respectively after 60 days. For all the tested fungi, the yield of reducing sugars and glucose increased significantly over the untreated controls, with Stereum hirsutum producing after 30 days pretreatment the best values (140 mM reducing sugars and 53 mM glucose); after this time no additional increments were observed. Pre-treated wood pieces showed changes in chemical composition in comparison to control samples. Total extractable substances contents are higher in wood pieces subjected to fungal action. However, lignin and alpha-cellulose values are lower in comparison to control samples. Some net holocellulose consumption could be observed, mainly during pretreatment with S. hirsutum by 45 and 60 days. Altogether these results support the potential of Eucalyptus globulus pre-treatment with S. hirsutum and L. edodes by periods not longer than 30 days, as a tool to increase the wood accessibility to depolymerizing action of hydrolytic enzymes. This preliminary study contributes to the identification of fungal pretreatment conditions for more effective cellulose degradation, a vital step in the utilization of monomer sugars process from cellulose to produce ethanol. Additional analysis of the solid and liquid fractions after saccharification is necessary to complement this information. © 2009 The Berkeley Electronic Press. All rights reserved.