A COMPARISON OF BARLEY AND MALT POLYPEPTIDES THAT INHIBIT GREEN MALT ENDOPROTEINASES

The brewing quality of a wort is strongly affected by its amino acid/p eptide/protein ratio, which in turn is determined by the endoproteinas es active during malting and mashing. In addition to the multiple endo proteinases present in germinating barley and malt, we previously show ed that inhibitors of these enzymes, which will affect the rate and ex tent of protein hydrolysis, occur in ungerminated barley. We are chara cterizing these inhibitors to determine how important they are to the malting and brewing processes. Contrary to reports by other researcher s, this study demonstrates that similar inhibitors are also present in kilned malt, at levels about 2.5 times higher than those of barley. B oth 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 inhibi tors are similar, and that the same is also true for the malt inhibito rs. I-a fractions from barley suppressed only cysteine class proteinas es, while those from malt inhibited a serine proteinase, in addition t o the cysteine proteinases.