VIEW ARTICLE    DOI: 10.1094/ASBCJ-53-0160

A Comparison of Barley and Malt Polypeptides that Inhibit Green Malt Endoproteinases (1). Berne L. Jones (2), U.S. Department of Agriculture, Agricultural Research Service, Cereal Crops Research Unit, Madison, WI 53705, and Department of Agronomy, University of Wisconsin, Madison, WI 53706; and Laurie A. Marinac, U.S. Department of Agriculture, Agricultural Research Service, Cereal Crops Research Unit, Madison, WI. (1) Presented at the 60th Annual Meeting, Toronto, Ontario, May 1994. Names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard of the product, and the use of the name by the USDA implies no approval of the product to the exclusion of others that may also be suitable. (2) Author to whom correspondence should be addressed. J. Am. Soc. Brew. Chem. 53(4):160-166, 1995. Accepted March 6, 1995. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. American Society of Brewing Chemists, Inc., 1995.

The brewing quality of a wort is strongly affected by its amino acid/peptide/protein ratio, which in turn is determined by the endoproteinases active during malting and mashing. In addition to the multiple endoproteinases present in germinating barley and malt, we previously showed that inhibitors of these enzymes, which will affect the rate and extent of protein hydrolysis, occur in ungerminated barley. We are characterizing these inhibitors to determine how important they are to the malting and brewing processes. Contrary to reports by other researchers, this study demonstrates that similar inhibitors are also present in kilned malt, at levels about 2.5 times higher than those of barley. Both barley and malt contain two classes of inhibitors are also present in kilned malt, at levels about 2.5 times higher than those of barley. Both barley and malt contain two classes of inhibitors I(a) and I(b). We have now separated the I(a) fractions (containing low-molecular-weight, proteinaceous compounds) from barley and malt into multiple forms by ion exchange chromatography. The separated I(a) fractions specifically inhibited the activities of particular electrophoretically separated green malt endoproteinases. All of the barley I(a) fractions restricted the activities of the same green malt endoproteinases, as did all of those from malt. This probably indicates that all of the barley inhibitors are similar, and that the same is also true for the malt inhibitors. I(a) fractions from barley suppressed only cysteine class proteinases, while those from malt inhibited a serine proteinase, in addition to the cysteine proteinases. Keywords: Barley, Endoproteinases, Germination, Malt, Malting quality, Proteinase inhibitors