Author
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Jones, Berne |
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Submitted to: Australian Barley Technical Symposium Proceedings
Publication Type: Proceedings Publication Acceptance Date: 8/11/1999 Publication Date: N/A Citation: N/A Interpretive Summary: To prepare good beer from malt (barley that has been germinated and then dried) the amount of protein in the malt that will dissolve in warm water ('soluble protein') needs to be regulated, and this is done by a group of enzymes that are called 'proteases'. We are trying to ascertain which of the many proteases in malt are involved in controlling the soluble protein levels and how they do this. To date, we have found that: a) there are about 40 different proteases in malt; b) these enzymes are not present in barley, but form during the malting process; c) the proteases are not destroyed during the malting process, but are rendered inactive during the latter stages of brewing; d) only certain of the enzymes are involved in adjusting the amount of soluble protein during malting and brewing; e) the majority of the 'soluble protein' that is present during brewing is formed by the proteases during the malting and brewing processes and; f) by adding specific chemical compounds during brewing, it is possible to either raise or lower the amount of soluble protein that is formed. These findings show that it is possible to systematically vary the amount of soluble protein present during brewing in order to produce better beer more efficiently. This can be done either by using plant breeding methods to alter the barley or by adjusting the malting and brewing methods used. This information benefits the brewing industry by showing how they can alter their malting and brewing methods to produce better beer more efficiently and benefits barley researchers by showing which aspects of barley they need to alter (using either classical plant breeding or 'molecular biology' methods) to produce improved barley cultivars. Technical Abstract: The endoproteinases that form during barley malting are important determinants of the soluble protein levels of brewing worts. We are determining which of these enzymes play important roles in solubilizing proteins during mashing and how endogenous barley and malt proteinase inhibitors affect this solubilization. We have used two methods, 'in solution' and 2-D IEF x PAGE, to measure the proteolytic activities of barley samples that were being malted. Our findings were: a) The great majority of the endoproteinases of malt were not present in the ungerminated barley, but formed during the 'germination' phase of the malting process; b) The activities of the 40 or more green malt endoproteinases were totally stable to kilning under standard conditions, up to at least 85C; c) The malt proteinases were stable throughout the 'protein rest' phase of mashing using the standard ASBC mash process, but were inactivated during the 'ramping' phase, as soon as the temperature was raised above approximately 60C; d) The addition of class-specific protease inhibitors to mashes showed that the cysteine-, aspartic- and metalloproteinases all played roles in the solubilization of proteins during mashing; e) About 23% of the soluble protein of a wort was preformed in the barley grain, 32% was solubilized during malting and the remaining 25% was released during mashing and; f) the soluble protein levels of worts were lowered by adding endogenous inhibitor preparations to mashes and enhanced by adding cysteine (or certain other reducing agents). These results show that it should be possible to expeditiously develop improved malting barleys and to alter mashing methods so that high quality beer can be produced more efficiently. |
