Endoproteases of barley and malt

During seed germination several seed biopolymers, including the storage proteins, must be hydrolysed to provide biochemical building blocks for the growing seedling. This process is particularly important in barley because under the guise of 'malting', it forms the basis of the malting and brewing industries. The steps involved in the enzymatic formation of 'soluble protein' during malting and in the 'mashing' phase of brewing are still not well understood. The barley proteins are initially solubilized by endoproteases and then further degraded by exopeptidases. The cysteine-class proteases probably play the most important roles, but their contributions are likely not as overwhelming as was thought previously. The metalloproteases are apparently also important players in protein solubilization, although their contributions have scarcely been examined. The characteristics of the purified aspartic class proteases imply that they are not important contributors to protein solubilization, but recent mashing studies indicate that they probably do play a minor role. All indications are that the barley and malt serine class proteases are not directly involved in storage protein hydrolysis during malting/mashing. More studies are needed to clarify the roles of the aspartic- and metalloproteases. One important aspect of further studies should be to ensure that appropriate biochemical methods are used, as well as conditions that are truly appropriate to commercial malting and mashing processes. (c) 2005 Elsevier Ltd. All rights reserved.