EVIDENCE FOR THE PRESENCE OF A PENTOSANASE INHIBITOR IN WHEAT FLOURS

The solubilisation, by a pentosanase preparation from Aspergillus nige r, of arabinoxylans from water-unextractable pentosans (WUP) isolated from wheat flour was much reduced when carried out in flour aqueous ex tracts as medium, instead of pure buffer. When flour extracts were pre viously heated at 100 degrees C, the extent of arabinoxylan solubilisa tion was almost restored. The heating at 100 degrees C and centrifugat ion of the flour extracts removed approximately one-third of the solub le protein but very low amounts of arabinoxylan. Increasing the concen tration of extracts decreased the extent of WUP arabinoxylan solubilis ation. There was slight variability between wheat cultivars Apollo, So issons and Thesee in the extent of the inhibitory effect. Compounds re sponsible for this effect were mainly present in wheat grain endosperm but also in bran. Different microbial xylanases from A. niger (Grinda myl S 100 and E1, an endoxylanase purified from this commercial prepar ation) and Trichoderma strains (Cl, a partially purified cellulase/hem icellulase complex, and the commercial preparations Veron HE and Multi fect XL) were strongly inhibited. Also the arabinofuranosidase activit y present in Grindamyl S 100 was inhibited but to a lower extent than xylanases. Pronase treatment and protein addition in the extracts had no effect on the level of inhibition. (C) 1998 Academic Press.