Process Study On Enzymatic Production Of Xylo-Oligosacchairdes With Steam Explosion Pretreatment

Xylooligosaccharides(XOS) is a kind of functional oligosaccharides which has a broadapplication prospects. This article investigated the manufacture of XOS by SteamExplosion(SE) pretreatment combined with enzymatic hydrolysis and the decoloration ofXOS by active carbon, with corncob as raw materials. The raw corncob was first presoakedby dilute sulfuric acid, and then the SE treatment conditions to maximum the extraction ofxylan were optimized; the enzymatic hydrolysis conditions of steam exploded corncob byefficient endo-xylanase for XOS production were optimized too; the XOS solution wasdecolorized by active carbon, experimental parameters were also optimized using orthogonalexperiments.First, corncob xylan was extracted by SE assisted by dilute sulfuric acid presoaking.Firstly, raw corncob was soaked by0.1%sulfuric acid for30mins at100℃Then xylan wasextracted from the corncob with the new catapult-style steam explosion equipment. Theoptimized SE conditions were: steam pressure of1.8MPa and pressure maintaining time of3min The corresponding extraction rate of corncob xylan reached22.33%(based on theweight of raw corncob) and an amount of XOS of39.96%(based on the total soluble sugar)was produced. SEM observation of the surface structure of the corncob before and after SEtreatment indicated that the effect of SE treatment was obvious, enabling an effectivedissolution of xylan from corncob.Second, the residue and the syrup of steam exploded corncob was hydrolyzed byendo-xylanase together, and the sugar composition of the enzymatic hydrolysate was analyzedby HPLC. In the four selected xylanases, xylanase2was the most suitable for the enzymatichydrolysis of steam exploded corncob. The optimal conditions were as follows: reactiontemperature of50℃, initial pH6.0, solid-liquid ratio of1:10,0.1%enzyme, reaction time of6h. Under this condition, the content of the soluble total sugar and reducing sugar in thehydrolysate increased41.71%and40.61%than that in the steam explosion extract, reaching7.91mg/ml and5.75mg/ml, respectively. HPLC analysis and calculation showed that thecontent of XOS is65.08%(based on the total soluble sugar).Third, the XOS solution was decolorized by active carbon which is one of the mostcommonly used decolorants in industry. The suitable range of the conditions were determinedusing the single factor method: decolorate temperature between70℃to80℃, decoloratetime between30min to60min, active carbon addition amount between20%to30%,oscillation frequency between140r/min to180r/min, the syrup solids content between20%to30%. On this basis, the optimum decolorate condition was reached by orthogonal experiments:decolorate temperature of80℃, decolorate time of60min, active carbon additive amount of25%, oscillation frequency of170r/min, syrup solids content of25%. Under this condition,the decolorate rate of the XOS solution was88.76%, with a loss of21.47%of the total sugar.