Protein: Difference between revisions
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Flavor stability is the ability of the beverage to resist changes to flavor, mainly due to oxidation. Proteins in the beer have a significant influence on flavor stability. | Flavor stability is the ability of the beverage to resist changes to flavor, mainly due to oxidation. Proteins in the beer have a significant influence on flavor stability. | ||
Protein thiols, which are present on cysteine residues in proteins (as discussed above), possess antioxidative capacity in beer and wort.<ref name=lund>Lund MN, Lametsch R, Sørensen MB. [https://onlinelibrary.wiley.com/doi/pdf/10.1002/jib.155 Increased protein–thiol solubilization in sweet wort by addition of proteases during mashing.] ''J Inst Brew.'' 2014;120(4):467–473.</ref> The concentration of free thiols correlates with the oxidative stability of beer because thiols remove reactive oxygen species (ROS).<ref name=lundm>Lund MN, Petersen MA, Andersen ML, Lunde C. [https://www.tandfonline.com/doi/abs/10.1094/ASBCJ-2015-0602-01 Effect of protease treatment during mashing on protein-derived thiol content and flavor stability of beer during storage.] ''J Am Soc Brew Chem.'' 2015;73(3):287–295.</ref> The major contribution to the protein thiol concentration in beer comes mainly from LTP1 because it is rich in cysteine and is a major component of beer protein.<ref name=lund/><ref name=lundm/><ref name=wumj>Wu MJ, Clarke FM, Rogers PJ, et al. [https://www.mdpi.com/1422-0067/12/9/6089/pdf Identification of a protein with antioxidant activity that is important for the protection against beer ageing.] ''Int J Mol Sci.'' 2011;12(9):6089–6103.</ref> In fact, beer LTP1 has been shown to scavenge one of the dominating radical compounds in beer, the 1-hydroxyethyl radical, at a rate similar to other reactive compounds in beer such as hop bitter acids.<ref name=lundm/> Thiols will react with almost all of the reactive oxygen species, which makes them especially important as far as beer aging is concerned.<ref name=wu/> A number of other proteins have also been identified in beer that contain several cysteine residues, so they could also contribute significantly to the thiol concentration in the beer.<ref name=lund/> In particular, yeast thioredoxin (TRX) is another thiol-rich protein suggested to provide defense against ROS.<ref name=wu/> | Protein thiols, which are present on cysteine residues in proteins (as discussed above), possess antioxidative capacity in beer and wort.<ref name=lund>Lund MN, Lametsch R, Sørensen MB. [https://onlinelibrary.wiley.com/doi/pdf/10.1002/jib.155 Increased protein–thiol solubilization in sweet wort by addition of proteases during mashing.] ''J Inst Brew.'' 2014;120(4):467–473.</ref><ref name=wumj/> The concentration of free thiols correlates with the oxidative stability of beer because thiols remove reactive oxygen species (ROS).<ref name=lundm>Lund MN, Petersen MA, Andersen ML, Lunde C. [https://www.tandfonline.com/doi/abs/10.1094/ASBCJ-2015-0602-01 Effect of protease treatment during mashing on protein-derived thiol content and flavor stability of beer during storage.] ''J Am Soc Brew Chem.'' 2015;73(3):287–295.</ref> The major contribution to the protein thiol concentration in beer comes mainly from LTP1 because it is rich in cysteine and is a major component of beer protein.<ref name=lund/><ref name=lundm/><ref name=wumj>Wu MJ, Clarke FM, Rogers PJ, et al. [https://www.mdpi.com/1422-0067/12/9/6089/pdf Identification of a protein with antioxidant activity that is important for the protection against beer ageing.] ''Int J Mol Sci.'' 2011;12(9):6089–6103.</ref> In fact, beer LTP1 has been shown to scavenge one of the dominating radical compounds in beer, the 1-hydroxyethyl radical, at a rate similar to other reactive compounds in beer such as hop bitter acids.<ref name=lundm/> Thiols will react with almost all of the reactive oxygen species, which makes them especially important as far as beer aging is concerned.<ref name=wu/> A number of other proteins have also been identified in beer that contain several cysteine residues, so they could also contribute significantly to the thiol concentration in the beer.<ref name=lund/> In particular, yeast thioredoxin (TRX) is another thiol-rich protein suggested to provide defense against ROS.<ref name=wu/> | ||
Note that the free thiol concentration diminishes as they are exposed to oxygen, removing the antioxidative ability of LTP1 and the other cysteine-rich proteins.<ref name=lund/><ref name=lundm/><ref name=wu>Wu MJ, Rogers PJ, Clarke FM. [https://onlinelibrary.wiley.com/doi/pdf/10.1002/jib.17 125<sup>th</sup> anniversary review: The role of proteins in beer redox stability.] ''J Inst Brew.'' 2012;118(1):1–11.</ref> However, even if the wort is fully oxidized during mashing, the disulfides (bound thiols) are subsequently reduced during fermentation, thus converting them to active free thiol antioxidants in the beer.<ref name=lund/><ref name=lundm/><ref name=wu/> Of course, oxygen-limited packaging is also extremely important to prevent degradation of beer flavor. | Note that the free thiol concentration diminishes as they are exposed to oxygen, removing the antioxidative ability of LTP1 and the other cysteine-rich proteins.<ref name=lund/><ref name=lundm/><ref name=wu>Wu MJ, Rogers PJ, Clarke FM. [https://onlinelibrary.wiley.com/doi/pdf/10.1002/jib.17 125<sup>th</sup> anniversary review: The role of proteins in beer redox stability.] ''J Inst Brew.'' 2012;118(1):1–11.</ref> However, even if the wort is fully oxidized during mashing, the disulfides (bound thiols) are subsequently reduced during fermentation, thus converting them to active free thiol antioxidants in the beer.<ref name=lund/><ref name=lundm/><ref name=wu/> Of course, oxygen-limited packaging is also extremely important to prevent degradation of beer flavor. Beers with higher levels of free thiols taste better (i.e. less oxidized).<ref name=wumj/> | ||
Reducing agents such as sulfite can re-activate oxidized thiols,<ref name=wu/><ref name=lundm/> although adding sulfite at packaging is | Reducing agents such as sulfite can re-activate oxidized thiols,<ref name=wu/><ref name=lundm/> although adding sulfite at packaging is not something we recommend. | ||
Science FYI! A possible working mechanism for its ROS-scavenging ability is proposed: LTP thiol(s) is oxidized to the sulfenic acid by oxidants such as H<sub>2</sub>O<sub>2</sub>, which results in the destruction of a peroxide molecule in 1:1 stoichiometry. The free thiol can be recovered by two sequential reactions (reactions 2 and 3). The reaction 2 generates a disulfide (LTP-SSR) through reaction with a small molecule (HS-R) such as yeast thioredoxin. The reaction 3 uses sulfite or phenolic compounds to generate free thiol from the disulfide for the next round elimination of ROS.<ref name=wumj/> | |||
Similar to sparkling wine, yeast-derived proteins can also positively affect the flavor stability of beer, even though massive yeast autolysis can generate off-flavors in beer.<ref name=picariello/> | |||
Similar to sparkling wine, yeast-derived proteins can also affect the flavor stability of beer | |||
===Foam=== | ===Foam=== |