| Currently,the production of functional xylo-oligosaccharides mainly relies on the concentrated alkali dissolution extraction and xylanase hydrolysis process,which has complex steps,high pollution,and large water consumption,seriously restricting its production scale and comprehensive economic benefits.In response to the above bottlenecks,this study explored the effects of organic acid pretreatment and hydrothermal pretreatment on the dissociation of sugarcane bagasse hemicellulose,as well as the impact of pretreatment on xylanase biodegradation to prepare low molecular weight xylo-oligosaccharides.Finally,a new technology was developed to produce low molecular weight xylo-oligosaccharides by using mild,non-toxic,and edible acetic acid as a catalyst for pretreatment combined with xylanase hydrolysis of the sugarcane bagasse hemicellulose.The main research results are as follows:(1)Hydrothermal pretreatment can promote the hydrolysis of sugarcane bagasse xylan components and prepare xylo-oligosaccharides by acetic acid generated from acetylation and hydrolysis.Increasing the reaction temperature and time can improve the yield of low molecular weight xylo-oligosaccharides,but it is prone to by-products(xylose and furfural).Therefore,its maximum yield is only 45.1%.In addition,the study found that under the conditions of 190°C and 40 min,65% of the raw material xylan was hydrolyzed,and with the combination of endo-xylanase hydrolysis,the yield of low molecular weight xylo-oligosaccharides could be increased to 54.5%,and the proportion of xylobiose and xylotriose exceeded 70%.(2)The effects of different types of acid on the one-step hydrolysis process for preparing xylo-oligosaccharides were explored.Firstly,a strong acidic cation exchange resin(NKC-9)was used as a recyclable solid acid catalyst for the acid hydrolysis of xylan to produce XOS.The highest yield of 47.7% was achieved under the conditions of 5% solid acid loading,131℃,and 42 min,and the recyclability of the solid acid catalyst demonstrated its cost-effective production strategy;Secondly,to better understand the relationship between xylan degradation and xylo-oligosaccharide yield,four types of acidic solutions with different p Ka values(sulfuric,maleic,lactic,and acetic)were used for xylan hydrolysis,and kinetic models were established based on the reaction rate and activation energy.The results showed that weaker organic acids were better suited for the production of XOS,with higher generation rates and lower xylose formation rates.The preferred order of these four acids for XOS production was:sulfuric acid < maleic acid < lactic acid < acetic acid.A convenient and reliable method for selecting acidic catalysts for the preparation of XOS from xylan was provided;Finally,using the most effective acetic acid as the catalyst,direct hydrolysis of sugarcane bagasse was performed.The highest yield of XOS was obtained under the optimized conditions of 170℃,50 min,and 5% HAc,with a yield of 53.14%.(3)Hydrothermal pretreatment mainly faces the problem of high temperature and long reaction time requirements for the equipment;while acid hydrolysis in one step mainly has the issue of high proportion of xylose and low proportion of main effective components(X2 and X3).Therefore,based on the research of preparing xylo-oligosaccharides from sugarcane bagasse by hydrothermal and acetic acid pretreatment,we designed a new technology of coupling acetic acid-assisted pre-hydrolysis with enzymatic(endo-xylanase and feruloyl esterase)hydrolysis to achieve efficient production of xylo-oligosaccharides rich in X2 and X3.2%,with a higher proportion of X2 and X3(67.2%).In addition,enzyme hydrolysis of xylo-oligosaccharide residues was studied,and the cellulose saccharification efficiency was effectively improved by introducing secondary acid treatment.Based on the above,about 167 g XOS and 300 g glucose can be produced from 1000 g sugarcane bagasse raw materials. |
