Study On Directional Compound Of Forest Cellulose Degrading Enzyme System And Synergistic Effect Of Enzymolysis

Lignocellulosic biomass is the most abundant biomass resource on the earth,characterized by wide source,universality and easy accessibility.Bioenzymatic hydrolysis can convert lignocellulosic biomass into reducing sugar to prepare bioethanol such as ethanol,which plays an important role in relieving the pressure of energy supply and reducing environmental pollution in China.However,the dense structure and high polymerization degree of lignocellulosic biomass lead to its difficulties in disassembly,separation and efficiency.The high cost of cellulase and incomplete enzyme system is another key problem that restricts the efficient enzymatic conversion of lignocellulose.In this study,the pretreatment method of poplar cellulose(Populus tomentosa),the cellulose degrading enzyme system and the compound enzyme and compound additive were studied in order to improve the enzymatic digestion efficiency of poplar cellulose and reduce the amount of cellulase at the same time,the main results are as follows:(1)The poplar cellulose was treated by a combination of chemical and mechanical methods,and then the effects of wet or dry hydrolysis process on the main properties of poplar substrate and cellulose conversion rate were compared by the analytical methods of component content,cellulose crystallinity,particle size,specific surface area and pore size.The results showed that the wet method was significantly more favorable to the hydrolysis of poplar cellulose due to the influence of lignin content,particle size,and porosity.A combination of chemical and mechanical pretreatment significantly improved the enzymatic efficiency of poplar wood.The combination of pretreatment with solid acid and organic solvent(GVL)and post-treatment with wet-milling could increase the conversion rate of poplar cellulose from untreated 4.79%to 91.93%,increased of 87.14%.(2)The activity of cellulose degrading enzymes produced by liquid fermentation of various genera of fungi and their applicability to the enzymatic digestion of poplar cellulose were investigated.The results showed that the crude enzyme solutions produced by the liquid fermentation of Trichoderma reesei ATCC 24449(TR)and Aspergillus niger SM24 had a more complete cellulose degrading enzyme system and were more effective for the enzymatic hydrolysis of pretreated poplar.However,such as Penicillium XZH-22(P22)and Phanerochaete chrysosporium(PC)have higher activities of lytic polysaccharide monooxygenase(LPMO),β-glucosidase,xylanase or auxiliary protein,which can effectively enhance poplar enzymatic hydrolysis.In addition,TR and SM24 have a good substitution effect on the use of commercial enzyme LLC02.The combination of TR with LLC02 and SM24 with LLC02 can achieve 94.77%and 91.65%,respectively,and the substitution rates of commercial enzymes were 90.9%and 46.7%,respectively,which can significantly reduce the use of commercial enzymes.(3)The results showed that xylanase,LPMO and auxiliary protein of PC could promote the enzymatic hydrolysis of poplar,and the cellulose conversion rate could be increased by 16.67%,4.31%and 4.5%,respectively.The complex enzyme consisting of 12 FPU/g cellulose cellulase and 600 U/g substrate xylanase and additive complex system consisting of 1%PEG8000(m/v)and 1%n-decanol(m/v)at 10%substrate concentration resulted in 80.75%of enzymatic conversion of pretreated poplar,which was increased by 27.81%compared to the blank control.The high-solid enzymatic digestion of poplar cellulose(40%substrate concentration)synergistic effect of the compond enzyme and the compond additive could achieve the glucose concentration of 204.57 g/L and the total sugar concentration of 224.44 g/L,which shows the potential to produce high concentration sugar solution under low enzyme load.