Quantitative study of the formation of endoproteolytic activities during malting and their stabilities to kilning

The proteinases of germinating barley (Hordeum vulgare L.) hydrolyze storag e proteins into amino acids and small peptides that can be used by the grow ing plant or, during brewing, by yeast. They are critical for the malting a nd brewing processes because several aspects of brewing are affected by the amounts of protein, peptide, and amino acids that are in the wort. This st udy was carried out to quantitatively measure when endoproteinases form in green malt and whether they are inactivated at the high temperatures that o ccur during malt kilning. Little endoproteolytic activity was present in un germinated barley, but the activities began forming 1 day into the "germina tion" phase of malting, and they were nearly maximal by the third germinati on day. Quantitative studies with azogelatin "in solution" assays showed th at the green malt endoproteolytic activities were not inactivated under com mercial kilning conditions that use temperatures as high as 85 degrees C bu t that some actually increased during the final kilning step. Qualitative ( 2-D, IEF x PAGE) analyses, which allow the study of individual proteases, s howed that some of the enzymes were affected by heating at 68 and 85 degree s C, during the final stages of kilning. These changes obviously did not, h owever, decrease the overall proteolytic activity.