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ARS Home » Midwest Area » Madison, Wisconsin » Cereal Crops Research » Research » Publications at this Location » Publication #111567


item Jones, Berne
item Marinac, Laurie

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/16/2000
Publication Date: N/A
Citation: N/A

Interpretive Summary: Malt is used to make beer. To make good beer, the malt needs to contain a specific, intermediate concentration of amino acids and small peptides. These compounds are formed in the malt by enzymes (proteinases) that degrade proteins. There are ways people can adjust their malting and brewing procedures to get either higher or lower amounts of these protein-hydrolyzing enzymes in their malt or beer. However, until now no one has known exactly when the enzymes form during the malting process or when they are destroyed during brewing. This work was carried out to determine when the enzymes form during malting and whether and when they are destroyed during malting. Knowledge of these things will allow maltsters and brewers to vary their procedures to maximize the efficiency of their processes and to produce higher quality beers and malts. We found that the proteinases form during the latter stages of malting and that they are not destroyed during the last stage of kilning, when high temperatures are used. However, the structures of the enzymes changed somewhat under these high temperatures. This means that maltsters do not have to work to lower the temperatures of these procedures. This work helps malt producers by showing them that they have a lot of latitude in how they can alter their methods to produce improved products and indicates to barley breeders and other researchers that there is no need for them to spend time developing malting barley varieties that contain more temperature resistant protein-degrading enzymes.

Technical Abstract: The proteinases of germinating barley hydrolyze storage proteins into amino acids and small peptides that can be used by the growing plant or, during brewing, by yeast. They are critical for the malting and brewing processes because several aspects of brewing are affected by the amounts of protein, peptide and amino acids that are in the wort. This study was carried out to quantitatively measure when endoproteinases form in green malt and whether they are inactivated at the high temperatures that occur during malt kilning. Little endoproteolytic activity was present in ungerminated barley, but the activities began forming one day into the 'germination' phase of malting and they were nearly maximal by the third germination day. Quantitative studies with azogelatin 'in solution' assays showed that the green malt endoproteolytic activities were not inactivated under commercial kilning conditions that use temperatures as high as 85C, but that some actually increased during the final kilning step. Qualitative (2-D, IEF x PAGE) analyses, which allow studying the individual proteases, showed that some of the enzymes were affected by heating at 68 and 85C, during the final stages of kilning. These changes obviously did not, however, decrease the overall proteolytic activity.