The sensitivity of the Bacillus subtilis Xyn A xylanase and its mutants to different xylanase inhibitors determines their activity profile and functionality during bread making.

The importance of inhibition sensitivity for xylanase functionality in bread making was investigated using mutants of the wild-type Bacillus subtilis xylanase (XBSTAXI), sensitive to Triticum aestivum xylanase inhibitor (TAXI). XBSNI, a mutant with reduced sensitivity to TAXI, and XBSTI, a mutant sensitive to all wheat endogenous proteinaceous inhibitors (TAXI, Xylanase Inhibiting Protein and Thaumatin-like Xylanase Inhibitor) were used. The higher inhibition sensitivity of XBSTAXI and XBSTI compared to XBSNI was associated with a respective 7 and 53 fold increase in enzyme dosage required for a maximal increase in bread loaf volume. XBSTI and XBSTAXI were only active during the mixing phase and the beginning of fermentation, while XBSNI was able to hydrolyze arabinoxylan until the end of fermentation. In spite of this difference in activity profile, no differences in loaf volume were observed for the different xylanases at optimal concentrations. Dough extensional viscosity analysis suggests that increased water availability as a result of xylanase activity favors starch-starch and starch-gluten interactions and drives the improvement in bread loaf volume.