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Phenolic compounds: Difference between revisions
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[[Category:Off flavors]] [[Category:Brewing chemistry]] | [[Category:Off flavors]] [[Category:Brewing chemistry]] | ||
[[File:Ellagic-acid.png|thumb|Polyphenolic structure of ellagic acid]] | [[File:Ellagic-acid.png|thumb|Polyphenolic structure of ellagic acid]] | ||
Phenolic substances (sometimes called tannins or polyphenols) are integral and abundant components of plant cell walls, where they serve as a natural defense system against microbial pathogens, insects, and herbivores, as well as reducing oxidative stress.<ref name=wangas/><ref name=len/><ref name=dabkar>Dabina-Bicka I, Karklina D, Kruma Z. [https:// | Phenolic substances (sometimes called tannins or polyphenols) are integral and abundant components of plant cell walls, where they serve as a natural defense system against microbial pathogens, insects, and herbivores, as well as reducing oxidative stress.<ref name=wangas/><ref name=len/><ref name=dabkar>Dabina-Bicka I, Karklina D, Kruma Z. [https://www.cabidigitallibrary.org/doi/pdf/10.5555/20113337376 Polyphenols and Vitamin E as potential antioxidants in barley and malt.] Conference Proceedings of the 6th Baltic Conference on Food Science and Technology FOODBALT-2011; May 5–6, 2011; Jelgava, Latvia.</ref><ref name=schwarz/> During the [[brewing]] process, a wide and complex array of phenolic compounds from [[grain]] and [[hops]] are released into the [[wort]] and therefore are always present in [[beer]]. These compounds play a key role in beer quality since they directly influence the flavor, color, and clarity of beer.<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><ref name=bsp>Briggs DE, Boulton CA, Brookes PA, Stevens R. [[Library|''Brewing Science and Practice.'']] Woodhead Publishing Limited and CRC Press LLC; 2004.</ref> The effects of these compounds are closely related to the amount of [[oxidation]] that occurs. Phenolic compounds readily scavenge oxygen radicals and therefore serve as natural [[antioxidants]], helping to protect grain and hop flavor compounds from oxidation, thereby improving [[flavor stability]]. As antioxidants, they also provide a [[health and safety|health benefit]] when consuming beer and wine. However, as the phenolic compounds oxidize during brewing or beer storage, they add a darker color, add [[haze]], and contribute a variety of off-flavors including [[astringency]] and harsh bitterness. When modified by certain types of yeast or bacteria, phenolic compounds can add distinct flavors such as spicy clove, pepper, or smoke. These types of flavors are usually undesirable and are generally referred to as ''phenolic off-flavor'' (POF). Despite this term, these flavors are an important part of some specialty beer styles such as [[weissbier]] and [[saison]]. | ||
The phenolic content of beer depends largely on brewing practice and raw materials.<ref name=aroshe/><ref name=wangas/><ref name=fumgal/> Beer exhibiting high phenolics content (and the related increase in [[antioxidants|antioxidant]] activity) displays better flavor quality, more stable [[flavor stability|flavor and aroma]], improved [[foam]] stability, and longer [[haze|shelf life]] (i.e. improved clarity) as compared with beer with less phenolics.<ref name=narfod>Nardini M, Foddai MS. [https://www.mdpi.com/1420-3049/25/11/2466 Phenolics Profile and Antioxidant Activity of Special Beers.] ''Molecules.'' 2020;25(11):2466.</ref> Due to these beneficial effects, interest is shifting towards preserving the phenolic compounds from the raw materials to the final beer.<ref name=wangas/><ref name=zhache>Zhao H, Chen W, Lu J, Zhao M. [https://www.sciencedirect.com/science/article/abs/pii/S030881460901022X Phenolic profiles and antioxidant activities of commercial beers.] ''Food Chem.'' 2010;119(3):1150–1158.</ref><ref name=zhali/><ref name=yangao/><ref name=sibpla/><ref name=gankub>Ganbaatar C, Kubáň V, Kráčmar S, Valášek P, Fišera M, Hoza I. [https://publikace.k.utb.cz/handle/10563/1006300 Liquid chromatographic determination of polyphenenols in Czech beers during brewing proces.] Potravinárstvo. 2015;9(1):24–30.</ref><ref>Niño-Medina G, Romo-Longoria JD, Ramírez-González IV, Martínez-Reyna OO, Urías-Orona V. [https://www.tandfonline.com/doi/abs/10.1094/ASBCJ-2017-2751-01 Phenolic content and antioxidant capacity level in commercial Mexican lager beers.] ''J Am Soc Brew Chem.'' 2017;75(2):156–158.</ref> With this in mind, brewers have numerous ways to improve the composition of phenolic compounds and the level of antioxidant activity in the finished beer.<ref name=len/><ref name=zhao/> Perhaps most importantly, brewers may choose to [[low oxygen brewing|minimize oxygen exposure]] during the brewing process, resulting in much greater natural antioxidant activity in the final beer while avoiding the negative effects of phenolic compounds. Various other production parameters also have a major impact on the level of phenolic compounds, such as [[milling]] intensity, [[mashing]] temperature(s), [[PVPP]] treatment, and [[filtration]], which can all affect the amount extracted from the malt and carried through to the beer.<ref name=cargui/> The choice and quantity of raw materials (including [[malt]], [[hops]], and [[tannin additives]]) is also important because different ingredients will contribute varying levels of phenolic compounds to the wort.<ref name=piafor>Piazzon A, Forte M, Nardini M. [https://pubs.acs.org/doi/abs/10.1021/jf101975q Characterization of phenolics content and antioxidant activity of different beer types.] ''J Agric Food Chem.'' 2010;58(19):10677–10683.</ref> Lastly, beer storage and [[packaging]] conditions can have a significant impact on the structure of phenolic compounds, which may lead to [[haze]] formation or changes to flavor.<ref name=zhao/> | The phenolic content of beer depends largely on brewing practice and raw materials.<ref name=aroshe/><ref name=wangas/><ref name=fumgal/> Beer exhibiting high phenolics content (and the related increase in [[antioxidants|antioxidant]] activity) displays better flavor quality, more stable [[flavor stability|flavor and aroma]], improved [[foam]] stability, and longer [[haze|shelf life]] (i.e. improved clarity) as compared with beer with less phenolics.<ref name=narfod>Nardini M, Foddai MS. [https://www.mdpi.com/1420-3049/25/11/2466 Phenolics Profile and Antioxidant Activity of Special Beers.] ''Molecules.'' 2020;25(11):2466.</ref> Due to these beneficial effects, interest is shifting towards preserving the phenolic compounds from the raw materials to the final beer.<ref name=wangas/><ref name=zhache>Zhao H, Chen W, Lu J, Zhao M. [https://www.sciencedirect.com/science/article/abs/pii/S030881460901022X Phenolic profiles and antioxidant activities of commercial beers.] ''Food Chem.'' 2010;119(3):1150–1158.</ref><ref name=zhali/><ref name=yangao/><ref name=sibpla/><ref name=gankub>Ganbaatar C, Kubáň V, Kráčmar S, Valášek P, Fišera M, Hoza I. [https://publikace.k.utb.cz/handle/10563/1006300 Liquid chromatographic determination of polyphenenols in Czech beers during brewing proces.] Potravinárstvo. 2015;9(1):24–30.</ref><ref>Niño-Medina G, Romo-Longoria JD, Ramírez-González IV, Martínez-Reyna OO, Urías-Orona V. [https://www.tandfonline.com/doi/abs/10.1094/ASBCJ-2017-2751-01 Phenolic content and antioxidant capacity level in commercial Mexican lager beers.] ''J Am Soc Brew Chem.'' 2017;75(2):156–158.</ref> With this in mind, brewers have numerous ways to improve the composition of phenolic compounds and the level of antioxidant activity in the finished beer.<ref name=len/><ref name=zhao/> Perhaps most importantly, brewers may choose to [[low oxygen brewing|minimize oxygen exposure]] during the brewing process, resulting in much greater natural antioxidant activity in the final beer while avoiding the negative effects of phenolic compounds. Various other production parameters also have a major impact on the level of phenolic compounds, such as [[milling]] intensity, [[mashing]] temperature(s), [[PVPP]] treatment, and [[filtration]], which can all affect the amount extracted from the malt and carried through to the beer.<ref name=cargui/> The choice and quantity of raw materials (including [[malt]], [[hops]], and [[tannin additives]]) is also important because different ingredients will contribute varying levels of phenolic compounds to the wort.<ref name=piafor>Piazzon A, Forte M, Nardini M. [https://pubs.acs.org/doi/abs/10.1021/jf101975q Characterization of phenolics content and antioxidant activity of different beer types.] ''J Agric Food Chem.'' 2010;58(19):10677–10683.</ref> Lastly, beer storage and [[packaging]] conditions can have a significant impact on the structure of phenolic compounds, which may lead to [[haze]] formation or changes to flavor.<ref name=zhao/> | ||
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== Structure and classification == | == Structure and classification == | ||
[[File:Phenol.png|thumb|Structure of phenol]] | [[File:Phenol.png|thumb|Structure of phenol]] | ||
The phenolic unit is an aromatic ring connected to a hydroxyl (OH) group, and this phenolic ring is connected other structural elements to form a variety of phenolic compounds.<ref name=aroshe>Aron PM, Shellhammer TH. [https://onlinelibrary.wiley.com/doi/pdf/10.1002/j.2050-0416.2010.tb00788.x A discussion of polyphenols in beer physical and flavor stability.] ''J Inst Brew.'' 2010;116(4):369–380.</ref> They constitute a very diverse group of substances whose components vary greatly in chemical structure and therefore differ in reactivity.<ref name=yangao>Yang D, Gao X. [https://www.sciencedirect.com/science/article/abs/pii/S0924224421001552 Research progress on the antioxidant biological activity of beer and strategy for applications.] ''Trends Food Sci Technol.'' 2021;110:754-764.</ref> Phenolic compounds exist not only individually, but also in bound form attached to other molecules such as esters, sugars (glycosides), and organic acids.<ref name=flomon>Floridi S, Montanari L, Marconi O, Fantozzi P. [https://pubs.acs.org/doi/abs/10.1021/jf0260040 Determination of free phenolic acids in wort and beer by coulometric array detection.] ''J Agric Food Chem.'' 2003;51(6):1548–1554.</ref><ref name=cargon>Carvalho DO, Gonçalves LM, Guido LF. [https://ift.onlinelibrary.wiley.com/doi/abs/10.1111/1541-4337.12218 Overall antioxidant properties of malt and how they are influenced by the individual constituents of barley and the malting process.] ''Compr Rev Food Sci Food Saf.'' 2016;15(5):927–943.</ref><ref name=Siqueira>Siqueira PB, Bolini H, Macedo GA. [https://www.researchgate.net/publication/49599952_O_PROCESSO_DE_FABRICACAO_DA_CERVEJA_E_SEUS_EFEITOS_NA_PRESENCA_DE_POLIFENOIS O processo de fabricação da cerveja e seus efeitos na presença de polifenóis. (The beer manufacturing process and its effects on the presence of polyphenols.)] ''Alimentos e nutrição.'' 2008;19(4):491–498.</ref><ref name=zhao/> Barley contains hundreds of different phenolic compounds<ref name=zhao/> and the structural classification is very complex,<ref name=cheyni>Cheynier V. [https:// | The phenolic unit is an aromatic ring connected to a hydroxyl (OH) group, and this phenolic ring is connected other structural elements to form a variety of phenolic compounds.<ref name=aroshe>Aron PM, Shellhammer TH. [https://onlinelibrary.wiley.com/doi/pdf/10.1002/j.2050-0416.2010.tb00788.x A discussion of polyphenols in beer physical and flavor stability.] ''J Inst Brew.'' 2010;116(4):369–380.</ref> They constitute a very diverse group of substances whose components vary greatly in chemical structure and therefore differ in reactivity.<ref name=yangao>Yang D, Gao X. [https://www.sciencedirect.com/science/article/abs/pii/S0924224421001552 Research progress on the antioxidant biological activity of beer and strategy for applications.] ''Trends Food Sci Technol.'' 2021;110:754-764.</ref> Phenolic compounds exist not only individually, but also in bound form attached to other molecules such as esters, sugars (glycosides), and organic acids.<ref name=flomon>Floridi S, Montanari L, Marconi O, Fantozzi P. [https://pubs.acs.org/doi/abs/10.1021/jf0260040 Determination of free phenolic acids in wort and beer by coulometric array detection.] ''J Agric Food Chem.'' 2003;51(6):1548–1554.</ref><ref name=cargon>Carvalho DO, Gonçalves LM, Guido LF. [https://ift.onlinelibrary.wiley.com/doi/abs/10.1111/1541-4337.12218 Overall antioxidant properties of malt and how they are influenced by the individual constituents of barley and the malting process.] ''Compr Rev Food Sci Food Saf.'' 2016;15(5):927–943.</ref><ref name=Siqueira>Siqueira PB, Bolini H, Macedo GA. [https://www.researchgate.net/publication/49599952_O_PROCESSO_DE_FABRICACAO_DA_CERVEJA_E_SEUS_EFEITOS_NA_PRESENCA_DE_POLIFENOIS O processo de fabricação da cerveja e seus efeitos na presença de polifenóis. (The beer manufacturing process and its effects on the presence of polyphenols.)] ''Alimentos e nutrição.'' 2008;19(4):491–498.</ref><ref name=zhao/> Barley contains hundreds of different phenolic compounds<ref name=zhao/> and the structural classification is very complex,<ref name=cheyni>Cheynier V. [https://www.sciencedirect.com/science/article/pii/S0002916523275115 Polyphenols in foods are more complex than often thought.] ''Am J Clin Nutr.'' 2005;81(1):223S–229S.</ref><ref name=gerbec/> and therefore discussion here will be limited. | ||
=== Phenolic acids and simple phenols === | === Phenolic acids and simple phenols === | ||
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Phenolic compound removal (at all stages): | Phenolic compound removal (at all stages): | ||
* [[Oxidation]] during mashing, boiling, and chilling promotes polymerization, which leads to precipitation and removal with spent grains or trub.<ref name=wangas/><ref name=habkos/><ref name=guicur/><ref name=karhan/><ref name=stephenson/> Oxidative polymerization occurring during beer storage further decreases phenolic content and causes [[haze]].<ref name=wangas/><ref name=habkos/><ref name=siqbol>Siqueira PB, Bolini HMA, Macedo GA. [https:// | * [[Oxidation]] during mashing, boiling, and chilling promotes polymerization, which leads to precipitation and removal with spent grains or trub.<ref name=wangas/><ref name=habkos/><ref name=guicur/><ref name=karhan/><ref name=stephenson/> Oxidative polymerization occurring during beer storage further decreases phenolic content and causes [[haze]].<ref name=wangas/><ref name=habkos/><ref name=siqbol>Siqueira PB, Bolini HMA, Macedo GA. [https://www.researchgate.net/profile/Helena-Bolini/publication/267193879_Polyphenols_and_antioxidant_properties_in_forced_and_naturally_aged_Brazilian_beer/links/55a7b27508aeceb8cad6794a/Polyphenols-and-antioxidant-properties-in-forced-and-naturally-aged-Brazilian-beer.pdf Polyphenols and antioxidant properties in forced and naturally aged Brazilian beer.] ''J Brew Distilling.'' 2011;2(3):45–50.</ref><ref name=marveg/><ref name=coljer/> Oxidation not only causes precipitation, but also degrades some phenolics to other types of compounds, such as quinones.<ref name=calcol/> Lower pH tends to increase polymerization.<ref name=sibpla>Šibalić D, Planinić M, Jurić A, Bucić-Kojić A, Tišma M. [https://link.springer.com/article/10.1007/s11696-020-01276-1 Analysis of phenolic compounds in beer: from raw materials to the final product.] ''Chem Zvesti.'' 2021;75(1):67–76.</ref> | ||
* [[Protein]]s bind and remove phenolic compounds.<ref name=cargui/> Interestingly, less oxidized polyphenols tend to precipitate more readily with proteins.<ref name=wangas/> Boiling for longer periods (over 60 minutes) causes increased elimination of phenolic compounds due to increased precipitation,<ref name=wangas/><ref name=sibpla/> possibly due to increased binding with proteins. | * [[Protein]]s bind and remove phenolic compounds.<ref name=cargui/> Interestingly, less oxidized polyphenols tend to precipitate more readily with proteins.<ref name=wangas/> Boiling for longer periods (over 60 minutes) causes increased elimination of phenolic compounds due to increased precipitation,<ref name=wangas/><ref name=sibpla/> possibly due to increased binding with proteins. | ||
* Stabilizing agents (such as [[PVPP]]) bind and remove phenolic compounds.<ref name=wangas/> | * Stabilizing agents (such as [[PVPP]]) bind and remove phenolic compounds.<ref name=wangas/> | ||