Impact and prospective of fungal pre-treatment of lignocellulosic biomass for enzymatic hydrolysis

The presence of lignin in lignocellulosic biomass leads to a protective barrier which prevents enzymes from being accessible to cellulose and hemicellulose for hydrolysis. As a result, pre-treatment is a must step for subsequent enzymatic hydrolysis. Bio pre-treatment is normally conducted at low temperatures and low pressures without using expensive equipment, chemical agents, reactors, and additional energy for lignin removal and biomass structure destruction. Therefore, it is a green, safe, and inexpensive method. White-rot fungi (WRF), a group of fungi (more than 1500 different species) are successfully applied in bioconversion processes such as sewage treatment, biopulping, conversion of forest and agricultural residues to animal feeds, and the production of edible or medicinal mushrooms. In the bio pre-treatment process, WRF are mostly used for secreting ligninolytic enzymes, a variety of donor substrates and selective degradation of lignin. Current research related to WRF bio pre-treatment is mainly focusing on the following four aspects: (i) selection of candidate strains for certain biomass materials; (ii) optimization of cultivation methods; (iii) characterization of fungal treated materials; and (iv) evaluation of combining bio pre-treatment with chemical or physicochemical approaches. Future prospects and recommended research work on applying WRF in bio pre-treatment are also briefly introduced and summarized in this review. These include (i) integrated methods (i.e. co-treatment with organic solvents, diluted acids, supercritical CO2 and ionic liquids) to resolve problems existing in fungal pre-treatment applications; (ii) mutation breeding and crossbreeding of fungal mycelia to obtain engineering strains; and (iii) integration of fungal pre-treatment with simultaneous saccharification and fermentation to produce biofuels and value-added products. (c) 2012 Society of Chemical Industry and John Wiley & Sons, Ltd