ARABINOXYLAN SOLUBILIZATION AND INHIBITION OF THE BARLEY MALT XYLANOLYTIC SYSTEM BY WHEAT DURING MASHING WITH WHEAT WHOLEMEAL ADJUNCT - EVIDENCE FOR A NEW CLASS OF ENZYME-INHIBITORS IN WHEAT

Three EBC worts were made with 100% barley malt and eight with 60% bar ley malt and 40% wheat, of which two had additions of a Bacillus subti lis endoxylanase. The xylose (Xyl) levels of centrifuged wort (indicat ive of arabinoxylan levels) made from 100% barley malt were 0.46, 0.70 , and 0.55% (% dry matter), while the corresponding malt water-extract able Xyl contents were 0.31, 0.44, and 0.41%. The Xyl levels in centri fuged worts from 60% barley malt and 40% wheat (0.37-0.58%) depended m ainly on the water-extractable arabinoxylan content of the starting ma terial. The endoxylanolytic levels of the malts had only minor effect on the resulting Xyl contents of the worts. The increase of Xyl levels during mashing with 40% wheat (0.05-0.10%) were 12-58% lower than 60% of the increase in Xyl with a corresponding 100% malt wort. The addit ion of the endoxylanase from B. subtilis increased the centrifuged wor t Xyl level. Experiments in which the endoxylanolytic activity of malt extracts was measured in the presence of wheat water-extractables pro vided evidence for the presence of one or more endoxylanase inhibitors in wheat that are inactivated by heat treatment. The wheat inhibitors however did not inactivate the B. subtilis endoxylanase.