Résumé
The functionality of the proteinaceous wheat xylanase inhibitor XIP-I in Aspergillus niger endoxylanase-aided breadmaking was investigated using small-scale breadmaking and in vitro experiments. At an optimal dosage for an increase in bread volume, the endoxylanase provoked a ∼15% increase of loaf volume in standard flour experiments, but the dough was significantly more sticky than in the control. No variations in bread volumes were observed in the presence of added XIP-I in endoxylanase dough but stickiness was much reduced. Arabinoxylan (AX) solubilisation from flour cell wall material was practically unaffected with XIP-I, and the viscosity of dough water extracts and AX intrinsic viscosity were slightly enhanced. In other breadmaking experiments using a flour from which water extractable material was inactivated, or a reconstituted flour (starch, gluten, water extractable arabinoxylans (WEAXs), water unextractable arabinoxylans (WUAXs)), no differences in loaf volumes were observed between control, endoxylanase and endoxylanase/XIP-I breads, but the high stickiness induced by endoxylanase was totally corrected by XIP-I. In these doughs, AX solubilisation was slightly affected by XIP-I whereas water extract viscosity and WEAX intrinsic viscosity were much higher than in endoxylanase doughs. In vitro experiments with purified AX and A. niger endoxylanase and XIP-I confirmed these findings, showing that the endoxylanase inhibition by XIP-I had more effect on the characteristics measured on WEAX (specific and intrinsic viscosities) than those measured on WUAX (AX solubilisation). Premixing substrate, endoxylanase and inhibitor in different combinations showed that XIP-I had a tendancy to bind WUAX, but not WEAX, which changed the balance between enzymic AX solubilisation and AX depolymerisation. As a result, a high viscosity of water extracts was preserved, which is beneficial for dough handling properties