VIEW ARTICLE    DOI: 10.1094/ASBCJ-55-0153

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. Winok Debyser (1), Laboratory of Food Chemistry, Katholieke Universiteit Leuven, Kardinaal Mercierlaan 92, B-3001, Belgium; Guy Derdelinckx, Centre for Malting and Brewing Science, Katholieke Universiteit Leuven, Kardinaal Mercierlaan 92, B-3001, Belgium; and Jan A. Delcour, Laboratory of Food Chemistry, Katholieke Universiteit Leuven, Kardinaal Mercierlaan 92, B-3001, Belgium. (1) Corresponding author. E-mail: <Jan.Delcour@agr.kuleuven.ac.be> Fax (+32) 16 32 19 97. J. Am. Soc. Brew. Chem. 55(4):153-156, 1997. Accepted September 17, 1997. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. American Association of Cereal Chemists, Inc., 1997.

Three EBC worts were made with 100% barley malt and eight with 60% barley malt and 40% wheat, of which two had additions of a Bacillus subtilis endoxylanase. The xylose (Xyl) levels of centrifuged wort (indicative of arabinoxylan levels) made from 100% barley malt were 0.46, 0.70, and 0.55% (% dry matter), while the corresponding malt water-extractable Xyl contents were 0.31, 0.44, and 0.41%. The Xyl levels in centrifuged worts from 60% barley malt and 40% wheat (0.37-0.58%) depended mainly on the water-extractable arabinoxylan content of the starting material. 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 addition of the endoxylanase from B. subtilis increased the centrifuged wort Xyl level. Experiments in which the endoxylanolytic activity of malt extracts was measured in the presence of wheat water-extractables provided 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. Keywords: Barley, Endoxylanase, Inhibitor, Wheat.

Tres mostos fueron preparados, siguiendo el método EBC, con 100% malata de cebada y ocho con 60% malta y 40% trigo, a dos de los cuales se les agregó una endoxilanasa obtenida de Bacillus subtilis. Los niveles de xilosa (Xyl) en los mostos centrifugados (indicativo de los niveles de arabinoxilanos) provenientes de 100% malta fueron 0.46, 0.70, y 0.55% (sobre base seca), mientras que los correspondientes contenidos de Xyl en los exractos acuosos de las maltas fueron 0.31, 0.44, y 0.41%. Los niveles Xyl en mostos centrifugados hechos con 60% malta y 40% trigo (0.37-0.58%) dependieron principalmente en el contenido de arabinoxilano soluble en agua de los materiales iniciales. La actividad endoxilanolítica de las maltas tuvo un efecto muy pequeño sobre los niveles Xyl de los mostos. Los incrementos de Xyl durante las maceraciones con 40% trigo (0.05-0.10%) fueron de 12 a 58% menores que 60% del incremento en Xyl con los mostos 100% malta. La adición de la endoxilanasa incrementó el nivel Xyl en los mostos centrifugados. Experimentos en los cuales se midió la actividad endoxilanolítica de extractos de malta en presencia de extractos acuosos de trigo, proporcionaron evidencia de la presencia de inhibidor(es) de endoxilanasa en trigo, el cual es inactivado por calor. El inhibido(es) del trigo no inactivó la endoxilanasa de Bacillus subtilis.