P79: Enhanced hydrolysis of lignocellulosic rice straw through introduction of fungal bioconversion process to the conventional physicochemical plus enzymatic procedures

The structure of lignocellulosic materials such as rice straw is composed of cellulose (50~55%), lignin(20~30%) and hemicellulose(15~20%). In biorefinary processes for the production of bio-based chemicals from lignocelluloses such as rice straw, it is well known that the degeneration process of lignin is a rate-limiting step, since the lignified materials effectively resist the attacks by the cellulose- and hemicellulose-degrading enzyme-complexes. In this study, in order to enhance the destruction level of the lignin component of rice straw and thus increase the amounts of fermentable sugars (glucose, xylose and arabinose), further bioconversion process was introduced using fungal fermentation broth, in addition to the conventional pretreatment steps (i.e., physicochemical plus enzymatic hydrolysis of the rice straw). Bioconversion process of the lignocellulosic rice straw was primarily carried out using the fungal strains screened in our laboratory, which were observed to actively proliferate on various lignocellulosic materials. First of all, rice straw was pretreated using NaOH solution at a moderate temperature and pH, and then the fungal fermentation broth containing various lignin-degrading enzyme-complexes(i.e., lignin peroxide, manganes peroxidase and laccase) was inoculated for further destruction of the pretreated lignocellulosic biopolymers. After this biological treatment step, final bioconversion process was conducted using the commercial cellulase-complexes for the enzymatic hydrolysis of the resulting cellulose and hemicellulose materials. The introduction of the additional fungal process was found to contribute to significant alterations of the lignocellulosic structure, thus leading to greater access of the cellulase-complexes to the physicochemically pretreated rice straw.