Impact of Inhibition Sensitivity on Endoxylanase Functionality in Wheat Flour Breadmaking

A Bacillus subtilis endoxylanase (XBSi) sensitive to inhibition by Triticum aestivum L. endoxylanase inhibitor (TAXI) and a mutant thereof (XBSni), uninhibited by TAXI, were used in straight-dough breadmaking to assess the importance of endoxylanase inhibition sensitivity on endoxylanase functionality in the process. With two European wheat flours, the loaf volume improving effect of XBSni at much lower enzyme dosages was substantially larger than that brought about by XBSi. This coincided with differences in arabinoxylan (AX) hydrolysis. Although XBSni had a lower substrate selectivity for water-unextractable arabinoxylan (WU-AX) than XBSi, the former solubilized significantly more WU-AX than XBSi. Because of inhibition, XBSi solubilized most of the WU-AX during mixing, whereas, with XBSni, the rate of solubilization decreased less with increasing processing time than that with XBSi. During fermentation and baking and at the highest dosage (600 U/kg of flour of XBSi and 60 U/kg of flour of XBSni), XBSni induced a stronger degradation of enzymically solubilized and water-extractable AX than XBSi. Taken together, the data clearly demonstrate that endoxylanases, which in vitro are inhibited by endoxylanase inhibitors and still are active in the breadmaking process, as demonstrated by their functional (bread volume) enhancing effect, gradually lose their activity in the process. Keywords: Endoxylanase; inhibition; arabinoxylan; breadmaking