12,587
edits
Protein: Difference between revisions
→Oxidation
| Line 33: | Line 33: | ||
Oxygen introduced into the mash causes the formation of larger polypeptide aggregates (linked via disulfide bridges, see below), which become insoluble at higher mash temperatures and which settle as a doughy layer on top of the spent grains in a traditional lauter tun.<ref name=adb/><ref name=poyri>Pöyri S, Mikola M, Sontag-Strohm T, Kaukovirta-Norja A, Home S. [https://onlinelibrary.wiley.com/doi/pdf/10.1002/j.2050-0416.2002.tb00550.x The formation and hydrolysis of barley malt gel-protein under different mashing conditions.] ''J Inst Brew.'' 2002;108(2):261–267.</ref><ref name=celus/><ref name=karhan/> This layer is often called the ''Oberteig'' (which means "upper dough" in German), and it can prevent clarification, and slow down or stop lautering and/or recirculation. Similar behavior is seen by the so-called "gel proteins", which are certain types of hordeins dissolved during malting. During mashing, they too can result in groups of a protein/polypeptide/lipid aggregates resulting from oxidation. Small starch granules, β-glucans, and pentosans, which in turn are linked to proteins, also take part in the formation of complexes, which lead to increased dough formation. They can also hinder the release of starch granules and thus the effect of the amylases. The formation of gel-protein is minimal at low temperature (e.g. 118°F, 48°C) possibly due to the action of proteases, but during and after the saccharification rests (e.g. 145°F, 63°C), the amount of gel-protein rises rapidly when the mash is oxidized. The ''Oberteig'' tends to become especially prominent if the mash is recirculated, or it can also form during vorlauf. | Oxygen introduced into the mash causes the formation of larger polypeptide aggregates (linked via disulfide bridges, see below), which become insoluble at higher mash temperatures and which settle as a doughy layer on top of the spent grains in a traditional lauter tun.<ref name=adb/><ref name=poyri>Pöyri S, Mikola M, Sontag-Strohm T, Kaukovirta-Norja A, Home S. [https://onlinelibrary.wiley.com/doi/pdf/10.1002/j.2050-0416.2002.tb00550.x The formation and hydrolysis of barley malt gel-protein under different mashing conditions.] ''J Inst Brew.'' 2002;108(2):261–267.</ref><ref name=celus/><ref name=karhan/> This layer is often called the ''Oberteig'' (which means "upper dough" in German), and it can prevent clarification, and slow down or stop lautering and/or recirculation. Similar behavior is seen by the so-called "gel proteins", which are certain types of hordeins dissolved during malting. During mashing, they too can result in groups of a protein/polypeptide/lipid aggregates resulting from oxidation. Small starch granules, β-glucans, and pentosans, which in turn are linked to proteins, also take part in the formation of complexes, which lead to increased dough formation. They can also hinder the release of starch granules and thus the effect of the amylases. The formation of gel-protein is minimal at low temperature (e.g. 118°F, 48°C) possibly due to the action of proteases, but during and after the saccharification rests (e.g. 145°F, 63°C), the amount of gel-protein rises rapidly when the mash is oxidized. The ''Oberteig'' tends to become especially prominent if the mash is recirculated, or it can also form during vorlauf. | ||
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/> 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> They are retained in the spent grains after lautering, but not in a form that reduces wort flow. | 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/> 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. | ||
To delve further into the chemistry, 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. 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=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. | To delve further into the chemistry, 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. 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=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. | ||