Evaluation of Some Wood Rotting Fungi for Bagasse Pretreatment in Ethanol Production
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Date
2011-06
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Addis Ababa University
Abstract
Lignocellulosic biomass is a sustainable feedstock for ethanol production compared to othersubstrates. In the ethanol generation process, pretreatment makes cellulose more accessible toenzymatic hydrolysis by modification of the lignin barrier. Biological pretreatment employsselective rot fungi that preferentially degrade lignin with minimum loss of polysaccharides.The system is not well developed; but is advantageous over other pretreatments becausereactions are enzymatic. These fungi produce ligninolytic enzymes, predominantly ligninperoxidase (LiP), manganese peroxidase (MnP) and laccase (Lac) in different combinations.Studies on biological pretreatments have shown lignin weight loss and improvement inethanol yield. However, only few well characterised white rots have been explored. The aimof this study was to evaluate the potential of 15 wood rotting fungi isolated from Ethiopia forpretreatment during 15 days solid state fermentation, using bagasse as lignocellulosicsubstrate. The production of ligninolytic enzymes by Fomitiporia aethiopica, F.pseudopunctata, Fomitopsis carnea and Vanderbylia vicina were reported for the first time inthis study. The white rots, F. aethiopica, Perenniporia tephropora, Inonotus sp. andPleurotus sajor-caju, were identified as relatively highly selective based on maximum andminimum productivity of ligninolytic and polysaccharide degrading enzymes, respectively.The pretreatment by the white rots caused ligninolysis and better cellulose digestibility wasobtained with higher lignin loss. Among the selective degraders, P. tephropora caused thehighest lignin loss (7.71%) and cellulose digestibility (29.44 %) after enzyme hydrolysis ofthe pretreated bagasse. This digestibility showed an improvement by 38.74 % in comparisonwith untreated bagasse. In addition to high MnP productivity (55.87 U/g), P. tephropora alsoproduced high titers of Lac (79.65 U/g) in contrast to the other selective degraders that mighthave attributed to better lignin loss. The ethanol yield from fermentation of cellulase enzymehydrolysed P. tephropora pretreated bagasse was 1.87 g/L, which was an improvement by27.21 % compared with untreated bagasse (1.47 g/L). Therefore, P. tephropora pretreatmentenhances ethanol production from bagasse through partial degradation of lignin, whichimproves the accessibility of cellulose to enzyme hydrolysis.
Key words: bagasse, ethanol, ligninolytic enzymes, pretreatment, rot fungi
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Keywords
bagasse ethanol ligninolytic enzymes pretreatment rot fungi