Xylo- and arabinoxylooligosaccharides from wheat bran by endoxylanases, utilisation by probiotic bacteria, and structural studies of the enzymes

Xylooligosaccharides (XOS) and arabinoxylooligosaccharides (AXOS) were produced from the insoluble arabinoxylan fraction of pretreated wheat bran by endoxylanases. The glycoside hydrolase (GH) family 10 xylanases GsXyn10A from Geobacillus stearothermophilus and RmXyn10A-CM from Rhodothermus marinus produced the AXOS A(3)X, A(2)XX and A(2 + 3)XX in addition to XOS. RmXyn10A-CM also produced XA(2 + 3)XX due to its non-conserved aglycone region accommodating additional arabinose substitutions in subsite +2. The GH11 enzymes, Pentopan from Thermomyces lanuginosus and NpXyn11A from Neocallimastix patriciarum had minor structural differences affecting hydrogen bonds in subsites -3 and +3, with similar hydrolysis profiles producing XA(3)XX as major AXOS and minor amounts of XA(2)XX but different ratios of X-3/X-2. In vitro analysis of the prebiotic properties of (A)XOS produced by Pentopan revealed nearly complete uptake of X-2 and X-3 by the probiotic bacteria Lactobacillus brevis and Bifidobacterium adolescentis. In contrast to previous reports, the GH43 arabinofuranosidase BaAXHd-3 from B. adolescentis cleaved alpha-1,3-linked arabinose on some single substituted AXOS.