Preparation of Xylooligosaccharides by Xylonic Acid Assisted Hydrolysis of Xylan and Its Separation and Recovery Process

Using reaction temperature, xylonic acid(XA-H) mass fraction and reaction time as independent variables, a response surface design was employed to optimize the yield of xylooligosaccharides(XOS) from acidic hydrolysis of the alkali extraction xylan obtained from corncob. And the Gluconobacter oxydans was used to bio-oxidize by-products xylose to XA-H. Then, XA-H and XOS products were simultaneously separated and recovered by bipolar membrane electrodialysis. The results indicated that the optimal conditions for producing XOS were solid-to-liquid ratio 1:10(g: mL), reaction temperature 170℃, mass fraction of XA-H 6%, and reaction time 22 min. Under the optimum conditions, the yield of XOS was 54.9%, while 18.5 g/L xylose was generated as byproduct. Sequentially, the xylose was converted into XA-H within 12 h with C. oxydans of 4 g/L(massconcentration 18.2 g/L, yield 90.9%) cells, and the total content of XA-H increased from 6% to 7.8%. Finally, the hydrolysate after biooxidation was subjected to electrodialysis for separating the XA-H and XOS; the corresponding recovery rates were 95% and 98%, respectively, the purity of XOS was increased from 30% to 75%.