Production of prebiotic xylooligosaccharides from alkaline extracted wheat straw using the K80R-variant of a thermostable alkali-tolerant xylanase

Agricultural by-products are raw materials of importance for increased utilization of renewable biomass. Wheat straw is a raw material of significant production volume and is in this work used for production of xylooligosaccharides (XOS). Extraction of xylan by dilute alkali was followed by hydrolysis using a variant of the alkali-tolerant Bacillus halodurans S7 endoxylanase A mutated at K8OR. The xylan yield was on average 56.5 g xylose equivalents per kg dried, ground wheat straw, with 1 arabinose per 12 xylose residues. The K8OR variant, which displayed higher specific activity than the wild type enzyme, was added at a load of 96 U/g extracted xylan. The XOS-yield (xylobiose-xylopentaose) was evaluated at time intervals in the temperature range of 50-65 degrees C, at pHs from 7 to 10. The enzyme was optimally active at 60 degrees C up to pH 9. Hydrolysis was completed within 7 h, resulting in 36% conversion of the xylan to predominantly xylobiose. Xylose content was low (2.4%) despite extended incubation, which is desirable for XOS-production. The XOS-containing hydrolysate was confirmed as a suitable carbon source for the putative probiotic strain Lactobacillus brevis DSM 1269, showing the applicability of the method to obtain prebiotic XOS. (C) 2014 Published by Elsevier B.V. on behalf of The Institution of Chemical Engineers.