Protein: Difference between revisions

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 All of these negative effects can be prevented by limiting oxygen in the mash, especially when oxygen-scavengers are also used.<ref name=poyri/><ref name=karhan/><ref name=mullerr/> In other words, [[low oxygen brewing]] improves lautering and recirculation speed due to the prevention of ''Oberteig'' and gel protein aggregate formation. However, low-oxygen mashing actually encourages effective coagulation of larger proteins such that they do not contribute to haze.<ref name=derouck>De Rouck G, Jaskula-Goiris B, De Causmaecker B, et al. [https://www.brewingscience.de/index.php?tpl=table_of_contents&year=2013&edition=0001%252F0002&article=82374 The impact of wort production on the flavour quality and stability of pale lager beer.] ''BrewingScience.'' 2013;66(1/2):1–11.</ref><ref name=karhan/> They are retained in the spent grains after lautering, but not in a form that reduces wort flow.
-Many proteins contain "thiol" groups, each made up of a sulfur and hydrogen (–SH) branch from an amino acid (especially cysteine) in the protein or polypeptide. These thiol groups can bond to each other, forming a "disulfide bridge" by linking the sulfur atoms together, removing the hydrogen atoms.<ref name=karhan/> This bonding occurs very rapidly under oxidative conditions; oxygen in the mash oxidizes the free thiols, creating links between molecules, thereby forming aggregates.<ref name=lund/><ref name=mullerr/><ref name=karhan>Karabín M, Hanko V, Nešpor J, Jelínek L, Dostálek P. [https://onlinelibrary.wiley.com/doi/full/10.1002/jib.502 Hop tannin extract: a promising tool for acceleration of lautering.] ''J Inst Brew.'' 2018;124(4):374–380.</ref> Certain enzymes in grain catalyze the oxidation of thiols, and these may include sulphydryl oxidase, glutathione oxidase, glutathione peroxidase and phospholipid-hydroperoxide glutathione peroxidase (but neither peroxidases nor lipoxygenases).<ref name=stephenson>Stephenson WH, Biawa JP, Miracle RE, Bamforth CW. [https://onlinelibrary.wiley.com/doi/pdf/10.1002/j.2050-0416.2003.tb00168.x Laboratory-scale studies of the impact of oxygen on mashing.] ''J Inst Brew.'' 2003;109(3):273–283.</ref> It's interesting that thiol oxidation is actually used in many scientific studies as a measure of wort oxidation, which is of particular interest to many breweries due to its correlation with gel formation.<ref name=celus/> Disulfide bonds may be broken by reducing (oxygen-scavenging) compounds such as [[sulfite]], resulting in the regeneration of the original protein thiol groups. Regenerated thiol groups can participate in new reaction cycles with reactive oxygen species (ROS) and, taken as a whole, act as catalysts for the removal of ROS by sulfite.<ref name=lundmn>Lund MN, Andersen ML. [https://www.tandfonline.com/doi/abs/10.1094/ASBCJ-2011-0620-01 Detection of Thiol Groups in Beer and Their Correlation with Oxidative Stability.] ''J Am Soc Brew Chem.'' 2011;69(3):163–169.</ref> This antioxidant mechanism includes [[lipid transfer protein]] 1 (LTP1) as an important thiol-containing protein. See [[Protein#Influence on flavor stability|Influence on flavor stability]] below, and [[Oxidation]] for more information.
+Many proteins contain "thiol" groups, each made up of a sulfur and hydrogen (–SH) branch from an amino acid (especially cysteine) in the protein or polypeptide. These thiol groups can bond to each other, forming a "disulfide bridge" by linking the sulfur atoms together, removing the hydrogen atoms.<ref name=karhan/> This bonding occurs very rapidly under oxidative conditions; oxygen in the mash oxidizes the free thiols, creating links between molecules, thereby forming aggregates.<ref name=lund/><ref name=mullerr/><ref name=karhan>Karabín M, Hanko V, Nešpor J, Jelínek L, Dostálek P. [https://onlinelibrary.wiley.com/doi/full/10.1002/jib.502 Hop tannin extract: a promising tool for acceleration of lautering.] ''J Inst Brew.'' 2018;124(4):374–380.</ref> Certain enzymes in grain catalyze the oxidation of thiols, and these may include sulphydryl oxidase (thiol oxidase), glutathione oxidase, glutathione peroxidase and phospholipid-hydroperoxide glutathione peroxidase (but neither peroxidases nor lipoxygenases).<ref name=stephenson>Stephenson WH, Biawa JP, Miracle RE, Bamforth CW. [https://onlinelibrary.wiley.com/doi/pdf/10.1002/j.2050-0416.2003.tb00168.x Laboratory-scale studies of the impact of oxygen on mashing.] ''J Inst Brew.'' 2003;109(3):273–283.</ref><ref name=kanbam>Kanauchi M, Bamforth CW. [https://www.themodernbrewhouse.com/wp-content/uploads/2019/02/BrewingScience_bamforth_82-84.pdf A Challenge in the study of flavour instability.] ''BrewingScience - Monatsschrift Brauwiss.'' 2018;71(Sept/Oct):82–84.</ref> It's interesting that thiol oxidation is actually used in many scientific studies as a measure of wort oxidation, which is of particular interest to many breweries due to its correlation with gel formation.<ref name=celus/> Disulfide bonds may be broken by reducing (oxygen-scavenging) compounds such as [[sulfite]], resulting in the regeneration of the original protein thiol groups. Regenerated thiol groups can participate in new reaction cycles with reactive oxygen species (ROS) and, taken as a whole, act as catalysts for the removal of ROS by sulfite.<ref name=lundmn>Lund MN, Andersen ML. [https://www.tandfonline.com/doi/abs/10.1094/ASBCJ-2011-0620-01 Detection of Thiol Groups in Beer and Their Correlation with Oxidative Stability.] ''J Am Soc Brew Chem.'' 2011;69(3):163–169.</ref> This antioxidant mechanism includes [[lipid transfer protein]] 1 (LTP1) as an important thiol-containing protein. See [[Protein#Influence on flavor stability|Influence on flavor stability]] below, and [[Oxidation]] for more information.
 ===Protein degradation===