Protein: Difference between revisions

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* Protein degradation lowers the amount of haze-forming materials (see [[Haze]]).<ref name=aldred/>

A wide variety of protease enzymes are involved in the protein degradation process, and besides amylases, they are the key degradation enzymes.<ref name=steiner/> Grain proteins are initially solubilized by '''endo'''proteases that break bonds in the middle of protein chains (endo- means inner), similar to the action of α-amylase on starch.<ref name=lund/><ref name=osman/><ref name=benesova/> Then they are further degraded by '''exo'''proteases that break off single amino acids from the ends of polypeptides (exo- means outer), similar to the action of β-amylase on starch. Besides degrading proteins, many of these enzymes also have other activities — ester modification, coagulation, and/or transpeptidase activity.<ref name=benesova>Benešová K, Běláková S, Mikulíková R, Svoboda Z. [http://kvasnyprumysl.eu/index.php/kp/article/download/95/74 Activity of proteolytic enzymes during malting and brewing.] ''Kvasný Prům.'' 2017;63(1):2–7.</ref> Proteolytic enzyme activity appears to be fairly consistent across widely different malt varieties, regardless of the breed or growing conditions.<ref name=osman/><ref name=jonesbl>Jones BL. [https://www.sciencedirect.com/science/article/abs/pii/S073352100500055X Endoproteases of barley and malt.] ''J Cereal Sci.'' 2005;42(2):139–156.</ref> Enzyme thermostability also appears consistent across barley types.<ref name=jones/>

A wide variety of protease [[enzymes]] are involved in the protein degradation process, and besides amylases, they are the key degradation enzymes.<ref name=steiner/> Grain proteins are initially solubilized by '''endo'''proteases that break bonds in the middle of protein chains (endo- means inner), similar to the action of α-amylase on starch.<ref name=lund/><ref name=osman/><ref name=benesova/> Then they are further degraded by '''exo'''proteases that break off single amino acids from the ends of polypeptides (exo- means outer), similar to the action of β-amylase on starch. Besides degrading proteins, many of these enzymes also have other activities — ester modification, coagulation, and/or transpeptidase activity.<ref name=benesova>Benešová K, Běláková S, Mikulíková R, Svoboda Z. [http://kvasnyprumysl.eu/index.php/kp/article/download/95/74 Activity of proteolytic enzymes during malting and brewing.] ''Kvasný Prům.'' 2017;63(1):2–7.</ref> Proteolytic enzyme activity appears to be fairly consistent across widely different malt varieties, regardless of the breed or growing conditions.<ref name=osman/><ref name=jonesbl>Jones BL. [https://www.sciencedirect.com/science/article/abs/pii/S073352100500055X Endoproteases of barley and malt.] ''J Cereal Sci.'' 2005;42(2):139–156.</ref> Enzyme thermostability also appears consistent across barley types.<ref name=jones/>

Malt '''endo'''proteases are complex and diverse, and are created in multiple forms during the germination of barley. They exhibit different optimal activity levels for pH, reaction temperature, and thermostability.<ref name=osman/> Barley malt contains over 40 endoproteinases, grouped into four classes: cysteine proteases, metalloproteases, aspartic proteases, and serine proteases.<ref name=zhang/><ref name=jones>Jones BL, Marinac L. [https://pubs.acs.org/doi/abs/10.1021/jf0109672 The effect of mashing on malt endoproteolytic activities.] ''J Agric Food Chem.'' 2002;50(4):858–864.</ref> The aspartic-, cysteine- and metalloproteinases likely play roles in solubilizing the storage proteins of barley and malt, whereas the serine proteinases apparently do not.<ref name=steiner/><ref name=jonesbudde/>