Submitted to: Journal of Cereal Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/13/2004
Publication Date: 1/20/2005
Citation: Jones, B., Budde, A.D. 2005. How various malt endoproteinase classes affect wort soluble protein levels. Journal of Cereal Science. 41:95-106. Interpretive Summary: The conversion of barley storage proteins to soluble proteins and amino acids is a critical process for the malting and brewing industries. This conversion is catalyzed by a group of enzymes called 'proteinases', but no one had ever determined which of the many proteinases present in germinating barley carried out this reaction. The authors studied this by adding chemicals to the brewing process that specifically stopped the action of each of the four 'classes' of proteinases that occur in 'mashes'. The inhibitors of the cysteine, metallo-aspartic proteinases lowered the amount of soluble proteins formed, indicating that these proteinases, but not the serine ones, were involved in breaking down the storage proteins. Adding an inhibitor mixture to mashes allowed a determination of when, during malting and mashing, the soluble proteins were released. A third of them were preformed in ungerminated barley, 50% were released during malting and 22% during the mashing portion of the brewing process. This information can be used by barley researchers to scientifically develop new barleys with improved brewing characteristics and/or by maltsters/brewers to alter their methods to more efficiently produce an improved product.
Technical Abstract: During the germination of seeds, storage proteins are degraded and the resulting amino acids are utilized by the growing seedling. In barley, this process is commercially important because it forms the basis for the malting and brewing industries. In this study, barleys and malts were mashed in the presence of compounds that specifically inhibited the four common proteinase classes. The efficacies of the proteinases in solubilizing proteins were cysteine ~ metallo > aspartic > serine ~ 0, which roughly reflected how the inhibitors affected the mash endoproteolytic activities. It was previously believed that only the cysteine enzymes were involved. All four enzyme classes affected the FAN concentration but none altered any of the other measured wort characteristics. With either single inhibitors or inhibitor mixtures, the effect of pH was as expected, based on earlier studies that indicated that cysteine and aspartic proteinases were most active at low pH values and the mettaloproteinases were only active at high pH. At the North American commercial mashing pH of 6.0, about one third of the soluble protein of a typical wort came from ungerminated barley, half was solubilized during malting and the remaining 22% was released during mashing.