Study On Preparation Of Xylo-oligosaccharides From Corn Straw Pith Core

Corn stalk pith is a kind of lignocellulose which was still not widely used.The hemicellulose is the main component of corn stalk pith,and it is the ideal raw material for the preparation of xylo-oligosaccharides.In this study,corn stalk pith was used as the raw material,and the xylan component was effectively separated from the hemicellulose.On the basis of elucidating the physical and chemical properties of the obtained products,the functional xylo-oligosaccharides were prepared by enzymatic hydrolysis.In the raw material pretreatment,the method of raw material pretreatment combining acid and alkali was adopted.The influence of the four influencing factors including NaOH alkali solution concentration,reaction temperature,reaction time and solid-liquid ratio on the yield of xylan were investigated.Orthogonal experiments shown that the essential conditions for preparing xylan from corn stalk pith core include NaOH concentration of 10%,reaction temperature of 85℃,solid-liquid ratio of 1:15（g/m L）,reaction time of 2 h.Under this circumstance,the yield of corn stalk pith core xylan reached 25.4%.Exploring the xylan samples extracted at different alkali concentrations and through color value analysis,the author discovered that the greater the absorbance of the extract,the greater the color value as the alkali concentration increases.The high concentration of NaOH solution easily breaks the side chains of xylan,resulting in an increase in the content of xylose.TG-DTG analysis showed that the xylan samples extracted with low alkali concentration had higher thermal stability.FT-IR,¹H-NMR and ¹³C-NMR analysis showed that the product separated from the raw material of corn stalk pith core has characteristic peaks of xylan,which the main chain isβ-D-xylose,and the side chain is composed of a small amount of L-arabinose and 4-O-methyl glucuronic acid.Using the isolated xylan as the substrate,the bio-enzymatic hydrolysis method is used to prepare xylo-oligosaccharides.Using Design-Expert 11 software,a functional model of enzymatic hydrolysis rate Y,enzyme addition amount A,enzymatic hydrolysis temperature B and enzymatic hydrolysis time C was established.If R² reached 0.9625,P value=0.0003<0.01,P value（loss of simulation error）=0.3118>0.05,it showed that the model was well-fitted.The second-order polynomial regression equation of response value Y to independent variables A,B,and C is fitted as follows:Y=81.94+1.725A+1.125B+1.075C+0.15AB-0.8AC-1.7BC-4.97A²-4.12B²-2.72C².The order of the interaction of various factors on the enzymatic hydrolysis rate was:A>B>C.The order of the interaction of various factors on the enzymolysis rate was:B×C>A×B>A×C.The essential conditions for preparing xylo-oligosaccharides by the response surface method include the amount of enzyme added of 516.35 IU/g,the enzymatic hydrolysis temperature of 51.12℃,and the enzymatic hydrolysis time of 4.28 h.Under this circumstance,enzymatic hydrolysis rate is 82.2%.After using high-performance ion chromatography to detect sugar components,the results showed that the main products of enzymatic hydrolysis were xylobiose and xylotriose,as well as trace amounts of xylose and xylotetraose.The structure analysis of the obtained xylo-oligosaccharides by FT-IR,¹H-NMR and¹³C-NMR showed that the side chains of xylo-oligosaccharides contained arabinose and uronic acid.TG-DTG analysis shows that the main pyrolysis temperature of the obtained xylo-oligosaccharides was between 240℃ and 380℃.At 600℃,the solid residue rate of xylo-oligosaccharides is 35.38%.