The bread-making functionalities of two Aspergillus niger endoxylanases are strongly dictated by their inhibitor sensitivities

A recent approach based on affinity chromatography with immobilised endoxylanase inhibitors was used to isolate two endoxylanases (EC 3.2.1.8) with different bread-making functionalities from an Aspergillus niger fermentation broth. TAXI (Triticum aestivum endoxylanase inhibitor) affinity chromatography yielded a TAXI- and XIP (endoxylanase inhibiting protein)-sensitive family 11 endoxylanase (24 kDa, pI 3.5), XIP affinity chromatography subsequently yielded a family 10 endoxylanase (36 kDa), only inhibited by XIP. While the first enzyme improves bread volume, the latter enzyme has no effect on bread quality whatsoever. The bread-making positive endoxylanase rather selectively hydrolyses water-unextractable arabinoxylan in an in vitro screening method, still performs/is active during bread-making and produces soluble arabinoxylan of high (>11.2 × 104 Da) and low molecular mass (≤11.2 × 104 Da). In contrast, the bread-making neutral endoxylanase in the in vitro assay displays a bias for water-extractable arabinoxylan and is immediately and almost completely inhibited during the early stages of bread-making. The results show that the functionalities of the purified A. niger endoxylanases in wheat bread-making are strongly dictated by their sensitivities towards wheat endoxylanase inhibitors.