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Enzymes: Difference between revisions
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* Lipid degradation and oxidation (see [[Lipids]]) | * Lipid degradation and oxidation (see [[Lipids]]) | ||
** '''Lipase''' (optimal 55–65°C, pH 6.8–7.0) degrades lipids & lipid hydroperoxides into glycerine plus free fatty acids, and/or hydroperoxides.<ref name=esslinger/><ref name=golston>Golston AM. The impact of barley lipids on the brewing process and final beer quality: A mini-review. ''Tech Q Master Brew Assoc Am.'' 2021;58(1):43–51.</ref><ref name=schwarzp>Schwarz P, Stanley P, Solberg S. [https://www.tandfonline.com/doi/abs/10.1094/ASBCJ-60-0107 Activity of lipase during mashing.] ''J Am Soc Brew Chem.'' 2002;60(3):107–109.</ref><ref name=mashing>Evans E. [[Library|''Mashing.'']] American Society of Brewing Chemists and Master Brewers Association of the Americas; 2021.</ref> | ** '''Lipase''' (optimal 55–65°C, pH 6.8–7.0) degrades lipids & lipid hydroperoxides into glycerine plus free fatty acids, and/or hydroperoxides.<ref name=esslinger/><ref name=golston>Golston AM. The impact of barley lipids on the brewing process and final beer quality: A mini-review. ''Tech Q Master Brew Assoc Am.'' 2021;58(1):43–51.</ref><ref name=schwarzp>Schwarz P, Stanley P, Solberg S. [https://www.tandfonline.com/doi/abs/10.1094/ASBCJ-60-0107 Activity of lipase during mashing.] ''J Am Soc Brew Chem.'' 2002;60(3):107–109.</ref><ref name=mashing>Evans E. [[Library|''Mashing.'']] American Society of Brewing Chemists and Master Brewers Association of the Americas; 2021.</ref> | ||
** '''Lipoxygenases''' (optimal 45–55°C, pH 6.3–7.0) oxidizes fatty acids into fatty acids hydroperoxides.<ref name=esslinger/><ref name=golston/><ref name=mashing/> | ** '''Lipoxygenases''' (optimal 45–55°C, pH 6.3–7.0) oxidizes fatty acids into fatty acids hydroperoxides.<ref name=esslinger/><ref name=golston/><ref name=mashing/> The function of lipoxygenase (LOX) during mashing is rather controversial. Lipoxygenase is suggested to be heat labile because only a minor part of the activity present in green malt survives kilning. However, this remaining part of LOX is known to be very stable towards heating. Almost 60% of the LOX activity of malt extract can survive for 1 h at a temperature of 67°C. LOX may survive temperatures as high as 95°C in spent grains. In addition, lipoxygenase purified from germinating barley has a pH optimum at 6.5.<ref name=poyri/> | ||
** '''Hydroperoxide lyase''' transforms lipid hydroperoxides through a series of steps into staling compounds such as trans-2-nonenal.<ref name=mashing/> | ** '''Hydroperoxide lyase''' transforms lipid hydroperoxides through a series of steps into staling compounds such as trans-2-nonenal.<ref name=mashing/> | ||