Refining xylo-oligosaccharide profiles by combining hot-water pre-hydrolysis with endoxylanase post-hydrolysis of corncob

Abstract

In this work, a two-step combined method (TSCM) combining hot-water pre-hydrolysis and endoxylanase post-hydrolysis was developed to directly and efficiently produce xylo-oligosaccharides (XOS) from corncob. Hot-water hydrolysis was employed to break down lignocellulosic xylan into soluble XOS, but this process resulted in the formation of larger molecules and more complex compositions of XOS. Endoxylanase hydrolysis disrupts the β-1, 4-glycosidic bonds of the main chain of xylan, which is capable of refining the XOS profiles into the desired degree of polymerization (DP) by selectively post-hydrolyzing the hot-water hydrolysate. Various kinetic models were simulated for the calculation and prediction of different preparation objectives using uniform design experimentation (UDE), and temperature was found to predominate in xylan degradation to XOS and by-products. A yield of 56.4 % XOS was obtained at 178 °C and 61 min of hot-water pre-hydrolysis of corncob. Endoxylanase could efficiently hydrolyze more than 70 % of larger xylo-oligomers to X2 and X3, but it had difficultly degrading the xylan in solid residues to XOS. Finally, 138.7 g of X2 and X3, accounting for 81 % of the XOS components, were produced from 1000 g of corncob. The approach combines hot water and enzymatic hydrolysis, making XOS production more sustainable, efficient and commercially viable, particularly with regard to direct production from straw-like agricultural residues, in addition to reducing chemical consumption and improving biomass conversion.