Study On Mimicking The Fungal Delignification For Promoting The Enzymatic Saccharification Of Lignocellulose

Lignin is the key barrier that limits the biotransformation of lignocellulosic wastes,such as straw and sawdust.As a major decomposer of plant biomass in wood,wood-rot fungi can efficiently degrade lignin by extracellular lignin degrading enzymes and free radicals,providing a new way of green and low energy consumption for efficient conversion of lignocellulose.In this study,we studied the delignification pathways of extracellular enzymes and free radicals secreted by wood rot fungi,and evaluated the degradation of lignin during different degradation processes.On this basis,by simulating the hydroxyl radical producing pathway of wood-rot fungi to achieve delignification and glycosylation rate increasing of bamboo.The main conclusions are as follows:The Fenton reaction was used to simulate the hydroxyl radical producing pathway of wood-rot fungi for lignin degradation.As the results showing,the hydroxyl radicals produced by the simulated system can degrade lignin efficiently,and the lignin degradation rate is positively correlated with the concentration of hydroxyl radicals,up to 45.11±1.06%.Lignin could effectively inhibit the decay of hydroxyl radicals.When the iron concentration was 2mM and the concentration of H₂O₂ was 0.5M,the content of hydroxyl radicals(OD₅₃₂)in the lignin-containing system was 102.52%higher than that of the control.The results of Gas Chromatography-Mass Spectrometry?GC-MS?analysis showed that lignin degradation products were mainly composed of short-chain fatty acids,long-chain and cyclic fatty acids and benzene ring organic acids,among which the content of short-chain fatty acid increased by 7 times,indicating that hydroxyl radicals made high molecular benzene rings of lignin open and then degraded them into short chain fatty acids to achieve lignin degradation.The degradation of lignin by laccase?Lac?and Versatile Peroxidase?VP?were studied to simulate the enzyme delignification pathway of wood-rot fungi.The results showed that the high enzyme load could promote the degradation of lignin to produce phenolics.When the Lac enzyme load was 1000U/g and the VP enzyme load was 80U/g,the content of soluble phenolics in degrading system were 2.4 times and 1.3 times of that in non-enzymatic treatment system.Enzymes'treatments could also lead to the re-polymerization of lignin,and the weight-average Molecular Weight?Mw?of lignin increased by 69.32%and 61.16%,respectively,after Lac and VP treatment.In addition,linoleic acid can promote the production of lipid peroxides in the in vitro degradation system of VP to reduce the lignin repolymerization.The hydroxyl radical delignification pathway of wood-rot fungi was simulated to enhance enzymatic hydrolysis of lignocellulose.The results showed that the content of hydroxyl radicals in the simulated system increased with the increase of H₂O₂ and iron concentration,and positively correlated with the sugar yield of bamboo.After treatment,the sugar yield of bamboo increased significantly,and the effect of free iron was more significant than that of chelated iron.After pretreatment,the sugar yield of bamboo was increased by 3.74 times compared with the control.The simulated system can effectively degrade lignin of bamboo to promote the enzymatic hydrolysis.when the concentration of iron is 4mM and the concentration of H₂O₂ is 4M,the maximum degradation rate of bamboo lignin is 22.33%.In summary,the in vitro simulation of fungal hydroxyl free radical delignification pathway can effectively degrade lignin of bamboo and promoting the hydrolysis of lignocellulose.This study presents a strategy for clean and mildly enhanced lignocellulosic biotransformation,which has certain potential in the field of lignocellulose conversion to bioenergy and chemical products.