Synergistic Pretreatment Of White Rot/Brown Rot Fungi Enhanced The Enzymatic Hydrolysis Of Corn Cobs

Lignocellulosic biomass.mostly from agricultural and forestry sources,has been regarded as a potential resource for the production of biofuels,chemicals and materials ascribing to its abundantly available,renewable,and cost-effective merits.Corn cobs,as plentiful agricultural wastes in China,are rich in carbohydrates and have been regarded as a potential resource.The most significant drawbacks of fungal treatment is the low conversion value.Thus,a two-step white rot-brown rot fungal pretreatment of corn cobs was proposed to enhance enzymatic hydrolysis efficiency and lower the severity requirement of pretreatment time.Moreover,the structure of isolated lignin was studied in this thesisCorn cobs were first pretreated by white rot fungi for 25 days,followed by brown rot fungi treated for 7 days.The results indicated that the enzymatic hydrolysis efficiency was dramatically improved while reducing the lengthy time requirement for the conventional fungal treatment process.The highest glucose yield of 83.0%was obtained by T.orientalis(Cui6300)/F.pinicola(Cui 12330)pretreatment.Hemicelluloses were selectively degraded after the pretreatment.SEM analysis illustrated that the structural disruption of pretreated samples occurred and might account for the enhancement of the hydrolysis efficiency.Additionally brown rot fungal treatment played a significant role in enzymatic hydrolysis enhancement.Cellulose content only decreased slightly in such a short time,which was in favor of hydrolysisAfter the white rot-brown rot fungal pretreatment,the cellulolytic enzyme lignin was isolated from corn cobs and the changes of lignin chemical structure were characterized.The results suggested that the chemical constitution of lignin was unchanged during the processing.The lignin of corn cobs was mainly composed of G-units and S-units,only small amount of H units,which was typical GSH-type and showed a predominance of(3-0-4' linkages.However,?3-O-4' linkages were cleaved during the fungal pretreatment that causing the decrease of molecular weight of lignin.The ratios of S/G increased from 0.49 to 0.90 and 0.92 respectively after the pretreatment,it confirmed that the G units of lignin were preferentially degraded than S units.Additionally,the p-coumarate and tricin were partially degraded in the processing.