Study On Enzymatic Mechanism Of Corn Stover Lignin And Simultaneous Saccharification For Ethanol Production

With the increasing shortage of non-renewable resources,biorefinery technology using lignocellulose such as corn stover as raw material has been rapidly developed.The principle is to convert cellulose and hemicellulose into glucose and xylose by enzymatic saccharification,and to convert glucose and xylose into platform compounds such as ethanol and lactose in subsequent reactions to prepare end-use chemicals.However,the dense structure of lignin hinders the accessibility of enzymes to the underlying cellulose and hemicellulose and reduces the efficiency of enzymatic digestion,so the degradation of lignin is a prerequisite for the efficient utilization of corn stover,which effectively promotes the release of cellulose and hemicellulose by degrading the lignin in the raw material to meet the requirements of resource utilization of lignocellulosic raw materials.Enzymatic degradation of lignin is an environmentally friendly method with the advantages of mild conditions and simple steps,which is an ideal means of lignin degradation and has become a hot research topic in recent years.In this study,we firstly isolated lignin with high purity and complete structure from corn stover,and studied the degradation effect of three pure enzymes,Laccase/Lac,Lingin Peroxidases/LiP and Manganese Peroxidases/MnP,on the lignin of corn stover.and systematic analysis of their degradation products.Based on the investigation of the sugar utilization process by the brewer’s yeast WXY12,which can ferment ethanol from glucose and xylose at the same time,we studied the simultaneous saccharification of ethanol production from enzymatically pretreated corn stover with the addition of cellulase and xylanase,and finally optimized the fermentation conditions and improved ethanol production by single-factor and response surface experiments,expecting to provide theoretical guidance for the biorefinement of ethanol from enzymatically pretreated corn stover.Theoretical guidance was expected to be provided for the enzymatic pretreatment of corn stover for biorefining ethanol.The main results of the study are as follows.(1)Three lignin-degrading enzymes,Lac,LiP and MnP,were used for enzymatic degradation of lignin in corn stover alone and in different combinations,with Lac alone having the best enzymatic effect with a degradation rate of 11.73%.When the three enzymes were combined in two combinations,the degradation effect of the treatment group containing Lac was better than that of the treatment group without Lac,indicating that Lac plays a key enzymatic role in the degradation of lignin.When three enzymes were combined to degrade lignin,the effect was better than single enzyme digestion or two enzymes combined to degrade,reaching 25.79% degradation rate.The degradation of lignin by the lignin-degrading enzyme system was found to be mainly in the destruction of the apparent structure of lignin and the breaking of the key chemical bonds of lignin by scanning electron microscopy and Fourier infrared detection.The degradation products were analyzed by GC-MS,and it was found that the lignin degradation enzymes system degraded lignin by opening the rings of the lignin polymer of corn stover into short-or long-chain fatty acids,and the small molecules of the products were greatly increased.This study confirmed that Lac,LiP and MnP can effectively degrade lignin and provided a theoretical basis for the biodegradation of these enzymes.(2)The fermentation of Saccharomyces cerevisiae WXY12 with different concentrations of monosaccharides(glucose and xylose)and mixed sugars showed that the strain could utilize both glucose and xylose,and its ability to utilize glucose was greater than that of xylose,and in mixed fermentation,the strain would utilize glucose first and xylose second,but the high concentration of sugar would inhibit the fermentation of the strain,resulting in a lower ethanol yield.When the initial concentration of glucose was 80 g/L,the fermentation of the strain produced the highest ethanol concentration of 32.56 g/L;when xylose was used as the substrate,the maximum ethanol concentration was 8.59 g/L when the xylose concentration was 20 g/L;when mixed sugar was fermented,the highest ethanol concentration was 37.56 g/L when the glucose concentration was 80 g/L and the xylose concentration was 20 g/L.(3)In this study,ethanol production from glucose and xylose in the hydrolysate of enzymatically pretreated corn stover was fermented by a simultaneous saccharification process using Saccharomyces cerevisiae WXY12,and the ethanol concentration was determined by gas chromatography,and the optimal conditions for its fermentation were determined by single-factor and response surface experiments: the initial p H was 5.5,the fermentation temperature was 37°C,the fermentation time was 33 h,the cellulase addition was 36 U/g of cellulase and 20 U/g of xylanase were added,and the maximum ethanol concentration was16.29 g/L under these conditions.