Study On Preparation Of Xylitol By Biological Fermentation Of Chenopodium Aestivum Straw

Xylol is a kind of pentachlorol,which has similar sweetness as sucrose.It does not need insulin to participate in the metabolism of human body,and has good anti-dental properties,because it has special application value in food industry and has attracted widespread attention.China is a large agricultural country,the annual output of crop straw is as high as 700 million tons,and quinoa straw is also one of them,but compared with other crop straw,its utilization rate is low.Quinoa straw contains a large amount of hemicellulose,and the xylose content in its structural unit is high.The conversion of hemicellulose from quinoa straw to xylose and further fermentation to produce xylitol are of great significance for the utilization of plant resources,environmental protection and sustainable development.The optimum technological parameters for producing xylitol from the hydrolysaccharide hydrolysate were determined.On this basis,the purification and crystallization conditions of xylitol fermentation liquid were studied.Through the experimental study,the following research results are obtained:1.The composition of quinoa straw was analyzed.By concentrated sulfuric acid hydrolysis,the content of cellulose,hemicellulose and lignin were 29.59%,20.32%and 19.21%,respectively.2.Hemicellulose hydrolysate was obtained by treating quinoa straw with dilute sulfuric acid.After the hemicellulose hydrolysate was detoxified by activated carbon,the optimum hydrolysis conditions of quinoa straw hydrolysate were determined by single factor experiment and orthogonal experiment.The optimum hydrolysis conditions were as follows:dilute sulfuric acid concentration 2%,solid-liquid ratio1:12,The hydrolysis temperature 125?and the reaction time 100 min.The xylose content of hydrolysate was 18.21 mg/mL.3.Xylitol was prepared from hemicellulose hydrolysate of quinoa straw fermented by Candida tropicalis.The optimum fermentation conditions of flask were determined by single factor and response surface method.The optimum conditions were as follows:the rotating speed of the flask 150 r/min,the temperature 30?,the initial xylose concentration 20 g/L,and the amount of nitrogen source 2 g/L yeast powder.4g/L tryptone,initial pH of fermentation broth 5.5,and inoculum amount of bacterial liquid 6%.Under these conditions,the xylitol yield?xylitol g/xylose g?reached 0.35g·g^-1.4.Xylitol was separated and purified by ethanol recrystallizing process.The impurities in xylitol fermentation broth were removed by ultrafiltration,ion exchange and activated carbon decolorization,and xylitol crystal was successfully crystallized,which laid a foundation for further research.