Bagasse pretreatment by some wood-rotting fungi in ethanol production

Abstract

Abstract. Tewolde D, Gessesse A. 2019. Bagasse pretreatment by some wood-rotting fungi in ethanol production. Bioteknologi 16: 21-30. Biomass from lignocellulosic materials is a sustainable feedstock for ethanol production. During ethanol production, pretreatment modifies the lignin barrier to make cellulose more accessible to enzymatic hydrolysis. The biological pretreatment involves selecting rot fungi that preferentially degrade lignin while retaining a minimum amount of polysaccharides. Despite not being well developed, the enzymatic nature of the reaction is an advantage over other pretreatment methods. These fungi produce ligninolytic enzymes, predominantly lignin peroxidase (LiP), manganese peroxidase (MnP) and laccase (Lac) in different combinations. Biological pretreatments have shown weight loss of lignin and improved yields of ethanol. However, only a few well-characterized white rots have been explored. This study evaluated 15 wood rotting fungi isolated from Ethiopia for pretreatment during 15 days of solid state fermentation using bagasse as a lignocellulosic substrate. The production of ligninolytic enzymes by Fomitiporia aethiopica, F. pseudopunctata, Fomitopsis carnea and Vanderbylia vicina were reported for the first time in this study. The white rots, F. aethiopica, Perenniporia tephropora, Inonotus sp. and Pleurotus sajor-caju, were highly selective based on maximum and minimum productivity of ligninolytic and polysaccharide degrading enzymes, respectively. The pretreatment by the white rots caused ligninolysis and better cellulose digestibility was obtained with higher lignin loss. Among the selective degraders, P. tephropora caused the highest lignin loss (7.71%) and cellulose digestibility (29.44%) after enzyme hydrolysis of the pretreated bagasse. This digestibility showed an improvement of 38.74 % in comparison with untreated bagasse. In addition to high MnP productivity (55.87 U/g), P. tephropora also produced high titers of Lac (79.65 U/g) in contrast to the other selective degraders that might have attributed to better lignin loss. The ethanol yield from the fermentation of cellulase enzyme hydrolyzed P. tephropora pretreated bagasse was 1.87 g/L, which improved by 27.21 % compared with untreated bagasse (1.47 g/L). Therefore, P. tephropora pretreatment enhances ethanol production from bagasse through partial degradation of lignin, which improves the accessibility of cellulose to enzyme hydrolysis.