Biological pretreatment of Eucalyptus grandis sawdust with white-rot fungi: Study of degradation patterns and saccharification kinetics

• White-rot fungi were used for biological pretreatment of Eucalyptus grandis sawdust.
• Biological pretreatment produced structural changes in the sawdust fibers.
• Pretreated sawdust was submitted to hydrolysis by a commercial cellulase.
• After pretreatment up to 20-fold more reducing sugars were liberated from sawdust.

The white-rot fungi Ganoderma lucidum, Phanerochaete chrysosporium, Pleurotus ostreatus, Pleurotus pulmonarius and Trametes sp were used for biological pretreatment of Eucalyptus grandis sawdust. Analysis by scanning electron microscopy and Fourier transform infrared spectroscopy showed that P. ostreatus and P. pulmonarius promoted more extensive selective modifications in the lignin content. Enzymatic hydrolysis of E. grandis sawdust cellulose with and without biological pretreatment was analyzed in terms of an equation that accounts for the initial delay that precedes the attainment of the maximal rate of hydrolysis, the presence and exhaustion of an easily hydrolysable fraction and the presence of a second fraction more difficult to be hydrolyzed. The equation could be fitted to all experimental curves including the hydrolysis curve of microcrystalline cellulose for comparison purposes. In general terms, the biological pretreatments diminished the initial delay, increased the easily hydrolysable fraction and generated a second hydrolysable fraction. The generation of an easily hydrolysable cellulose fraction obeyed the following decreasing sequence: P. ostreatus (16.7% of total cellulose) > P. pulmonarius (15.4%) > Trametes sp. (10.1%) ≫ P. chrysosporium (2.8%) ≈ no treatment (2.8%). The generation of the second hydrolysable fraction was more efficient in the case of P. pulmonarius and P. ostreatus pretreatments. For the latter, the total amount of reducing sugars released after 48 h of saccharification of sawdust was increased from 2.5 μmol/mL to 48.0 μmol/mL.

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