Co-Production Of Xylooligosaccharides And Monosaccharides By Acetic Acid/Sodium Acetate Pretreatment Combined With Enzymatic Hydrolysis Of Lignocellulosic Biomass

In this work,a novel strategy was proposed for the efficient preparation of xylooligosaccharides(XOS)by acetic acid/sodium acetate(AC/SA)pretreatment combined with xylanase hydrolysis using poplar and corncob as raw materials.The hydrolysis conditions were optimized for the preparation of XOS by AC/SA hydrolysis,the effect of xylanase hydrolysis on the XOS yield and polymerization distribution was investigated,and the effect of poplar lignin content on the yield and purity of XOS was investigated.The preparation of monosaccharides was studied by cellulase hydrolysis of solid residues,thus,a new strategy was obtained for the efficient preparation of XOS and monosaccharides from poplar and corncob by this system hydrolysis.Finally,the characteristics of AC/SA hydrolysis of xylan were also investigated,and the effects of cellulose and lignin on xylan hydrolysis were examined to reveal the law of XOS production from xylan in AC/SA hydrolysis system.The results of the study can provide a theoretical basis and scientific data for the preparation of XOS and monosaccharides from wood fiber raw materials in an efficient,clean and low-cost method.The main research results are as follows:1.By utilising poplar as the study subject,single-factor experiments were used to explore the effects of AC/SA concentration,molar ratio,hydrolysis duration,and temperature on xylan hydrolysis for XOS production.When poplar was hydrolyzed with AC/SA solution at a concentration of 0.15 M and a molar ratio of 3.0 at 175 °C for 60 min,followed by the hydrolysis of the AC/SA hydrolysate with xylanase loading of 10 U/m L for 24 h,the high yield of XOS was42.1%.The production of xylose and other by-products was significantly lower,implying a high purity of XOS produced from poplar by AC/SA hydrolysis.2.The removal of lignin and the yield of XOS were shown to have a positive linear relationship.Hydrogen peroxide/acetic acid pretreatment of poplar achieved 84.0% of lignin removal and higher than 90% of carbohydrate retention,optimizing AC/SA hydrolysis in combination with xylanase hydrolysis of poplar solid residue improved XOS yield to 55.7%.Furthermore,preferential lignin removal lowered xylose and by-product generation while improving XOS purity.The cellulose accessibility of poplar solid residue was significantly improved and hydrophobicity was reduced as a result of lignin removal and xylan hydrolysis,and the cellulose-rich solid residue showed satisfactory cellulase saccharification properties.91.3% of glucose and 88.4% of xylose were produced using cellulase hydrolysis with a loading of 20 FPU/g DM for 72 h.3.A two-stage AC/SA hydrolysis combined with enzymatic hydrolysis was proposed for the preparation of XOS from corncob.Based on the optimized molar ratio of AC/SA and hydrolysis temperature,the first stage of AC/SA hydrolysis combined with xylanase hydrolysis yielded 64.6%of XOS from corncob,and the second stage of AC/SA hydrolysis of corncob solid residue released10.1% of XOS.This sequential hydrolysis process yielded only 8.6% xylose and low content of by-products,meaning that the obtained XOS were of high purity.The 1% sodium hydroxide treatment was effective in removing lignin from corncob solid residue,improving the yield of cellulase hydrolysis.4.The degradation pattern of carbohydrates in the acetic acid/sodium acetate system was investigated using Avicel and corncob xylan as materials.In the AC/SA hydrolysis,no degradation products were detected in the supernatant of Avicel hydrolysis.Compared to acetic acid hydrolysis,AC/SA hydrolysis of corncob xylan produced 62.6% less xylose and 2.4% more XOS,while compared to autohydrolysis,XOS yield increased by 24.2% but only 9.4% more xylose was produced,implying that AC/SA hydrolysis was more favorable for the highly selective conversion of xylan to XOS,meaning that AC/SA hydrolysis more favorable for the highly selective conversion of xylan to XOS.Avicel and lignin inhibited the hydrolysis of corncob xylan by 4.2%-6.6% and 22.3%-88.7%,but did not affect the degradation characteristics of xylan in different hydrolysis systems.Based on the dual objectives of preparing high yield and high purity XOS,a new strategy was proposed for the preparation of XOS by combined AC/SA pretreatment with enzymatic hydrolysis.Compared with the traditional acid hydrolysis,autohydrolysis and alkali extraction-enzyme hydrolysis,this combined hydrolysis strategy achieved highly selective conversion of xylan to XOS,significantly improved the yield and purity of XOS,simplified the process and operation,and had better application prospects.