Pretreatment Of Jerusalem Artichoke Straw For Fermentative Production Of Acetoin By Hydroxylamine Ionic Liquids

Based on concerns about the depletion of fossil fuels and climate warming,the production of bio-based chemicals by biological methods is favored,and the use of non-food crop Jerusalem artichoke straw(JAS)to replace traditional carbon sources to produce bio-based chemicals is an important research direction.However,JAS was difficult to be directly utilized by enzymes and microorganisms due to its complex structure,so it needed to be pretreated to improve the accessibility of enzymes to cellulose and hemicellulose.Therefore,in this project,JAS was used as raw material,and hydroxylamine ionic liquid was used to pretreat it.The ILs were screened from the perspectives of enzymatic hydrolysis effect,water tolerance,toxicity to B.subtilis and the generation of inhibitors,and optimized by response surface methodology.Finally,a four-carbon platform compound acetoin was used as the product to study the fermentation and utilization of JAS,which provided a reference for the development of highefficiency and low-cost lignocellulose pretreatment technology.First,six kinds of hydroxylamine ionic liquids were synthesized in this experiment,characterized by FTIR and NMR,and the pretreatment mechanism was analyzed combined with physicochemical properties.Studies have shown that the pretreatment effect of hydroxylamine ionic liquid on lignocellulose is affected by its hydrogen bond alkalinity and the solubility of lignin.Based on factors such as pretreatment efficiency,water tolerance,residue after washing,and the effect on the growth and metabolism of acetoin in B.subtilis,EOAA was selected as the best IL.In addition,EOAA pretreatment produced fewer inhibitors.When adding EOAA at a concentration of no more than 0.3 mol/L to the fermentation medium,the maximum cell density increased by 25%.While the total concentration of acetoin and 2,3-butanediol at 0.1 mol/L EOAA was 15% higher than that of the blank control group.Single factor and response surface optimization were carried out on the pretreatment time,temperature and liquid-solid ratio of EOAA pretreatment conditions.The optimized pretreatment conditions were: After pretreatment at 170 °C for 5 h,the liquid-solid ratio in the system was 18.At this time,the recoveries of cellulose and hemicellulose were about 87% and75%,and 64% glucose yield and 66% xylose yield could be obtained by enzymatic hydrolysis for 24 hours under the condition of 10wt% cellulase immobilization.Transcriptome sequencing was used to analyze the reason why EOAA promotes the growth and metabolism of B.subtilis.The results showed that 0.1mol/L EOAA could promote the up-regulation of the bud ABC operon transcriptional genes that regulate the synthesis of acetoin and 2,3-butanediol in the bacterial metabolic pathway,which was the main reason for the significant increase in total product yield.And the related transcription genes regulating key enzymes in the glycolytic pathway were up-regulated,revealing the reason why 0.1 mol/L EOAA accelerated the rate of glucose consumption.In addition,it was found that the transcriptional genes related to spore synthesis were all down-regulated.Spore is a selfprotection mechanism of Bacillus under harsh conditions.It can be seen that the addition of 0.1mol/L EOAA was more beneficial to the growth of B.subtilis.Finally,the pretreated JAS was used for high-solid enzymatic hydrolysis and fermentation,and the enzyme addition amount and feeding times of high-solid enzymatic hydrolysis were optimized.The optimized conditions were as follows: adding 45 FPU/g JAS cellulase CTec2,and enzymatic hydrolysis without feeding for 72 h under the condition of 30wt% immobilization,135.1 g/L glucose and 46.0 g/L xylose were obtained by enzymatic hydrolysis.Using this enzymatic hydrolysate as carbon source for batch fermentation,the final yield of the target product reached 82.8 g/L,compared with the control group with sugar as carbon source,the yield increased by 36.4%.