Enzymes: Difference between revisions

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* Phenolic compound release or oxidation (see [[Phenolic compounds]], [[Oxidation]])

** '''Polyphenol oxidase''' (optimal 60–65°C, pH 6.5–7.0) oxidizes polyphenols, especially lower molecular weight polyphenols (e.g. catechin).<ref name=esslinger/><ref name=quibai>Quinde-Axtell Z, Baik BK. [https://pubs.acs.org/doi/abs/10.1021/jf060974w Phenolic compounds of barley grain and their implication in food product discoloration.] ''J Agric Food Chem.'' 2006;54(26):9978–9984.</ref><ref name=quipow>Quinde-Axtell Z, Powers J. Baik BK. [https://onlinelibrary.wiley.com/doi/abs/10.1094/CC-83-0385 Retardation of discoloration in barley flour gel and dough.] ''Cereal Chem.'' 2006;83(4):385–390.</ref>

** '''Polyphenol oxidase''' (optimal 60–65°C, pH 6.5–7.0) oxidizes polyphenols, especially lower molecular weight polyphenols (e.g. catechin).<ref name=esslinger/><ref name=quibai>Quinde-Axtell Z, Baik BK. [https://pubs.acs.org/doi/abs/10.1021/jf060974w Phenolic compounds of barley grain and their implication in food product discoloration.] ''J Agric Food Chem.'' 2006;54(26):9978–9984.</ref><ref name=quipow>Quinde-Axtell Z, Powers J. Baik BK. [https://onlinelibrary.wiley.com/doi/abs/10.1094/CC-83-0385 Retardation of discoloration in barley flour gel and dough.] ''Cereal Chem.'' 2006;83(4):385–390.</ref> polyphenol oxidases catalyze the oxidation of polyphenols.<ref name=adb/>

** '''Feruloyl esterase''' AKA '''ferulic acid esterase''' AKA '''cinnamoyl esterase''' (optimal activity 40–50°C, pH 5.2–6.6) liberates phenolic acids (mainly [[ferulic acid]]) from [[beta-glucans and arabinoxylans|arabinoxylans]].<ref name=adb/><ref name=schwarz>Schwarz KJ, Boitz LI, Methner FJ. [https://www.tandfonline.com/doi/abs/10.1094/ASBCJ-2012-1011-02 Release of phenolic acids and amino acids during mashing dependent on temperature, pH, time, and raw materials.] ''J Am Soc Brew Chem.'' 2012;70(4):290–295.</ref> Inactive at 65°C and above.<ref name=wangas>Wannenmacher J, Gastl M, Becker T. [https://ift.onlinelibrary.wiley.com/doi/abs/10.1111/1541-4337.12352 Phenolic substances in beer: Structural diversity, reactive potential and relevance for brewing process and beer quality.] ''Compr Rev Food Sci Food Saf.'' 2018;17(4):953–988.</ref>

** '''β(1-4)-endoxylanase''' releases xylooligosaccharides<ref name=schwarz/>

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* Non-specific oxidation (see [[Oxidation]])

** '''Peroxidase''' (optimal >60°C, pH 6.2) generates free radicals from various organic and inorganic substrates.<ref name=esslinger>Krottenthaler M, Back W, Zarnkow M. Wort production. In: Esslinger HM, ed. [[Library|''Handbook of Brewing: Processes, Technology, Markets.'']] Weinheim, Germany: Wiley-VCH Verlag GmbH & Co. KGaA; 2009.</ref> Requires [[iron]] coenzyme.<ref name=bsp/>

** '''Peroxidase''' (optimal >60°C, pH 6.2) generates free radicals from various organic and inorganic substrates.<ref name=esslinger>Krottenthaler M, Back W, Zarnkow M. Wort production. In: Esslinger HM, ed. [[Library|''Handbook of Brewing: Processes, Technology, Markets.'']] Weinheim, Germany: Wiley-VCH Verlag GmbH & Co. KGaA; 2009.</ref> Requires [[iron]] coenzyme.<ref name=bsp/> Peroxidase can retain its activity even at 80°C.<ref name=poyri/> Peroxidases catalyze the oxidation of polyphenols.<ref name=adb/> Barley malt contains remarkably high activity of the many peroxidase iso-enzymes, giving evidence for the importance of hydrogen peroxide reactions.<ref name=muller95/>

* Other