Polyphenols in beer

The polyphenols in beer, fruit juices, and tea are typically members of the flavan-3-ols (see Fig. 2.8) and the proanthocyanidins constructed from them. 

Dvorakova M, Hulin P, Karabin M, Dostalek P. 2007. Determination of polyphenols in beer by an effective method based on solid-phase extraction and high performance liquid chromatography with diode-array detection. Czech J. Food Sci 25 182-188. 

Mikyska A, Hrabak M, Haskova D, and Srogl J. The role of malt and hop polyphenols in beer quahty, flavour and haze stabihty. J. Inst. 

Malt contains 90-400 ppm of procyanidin B-3 of which half is extracted during infusion mashing but considerable losses occur during wort boiling and fermentation (Table 14.9) [52]. Increasing the length of the boil reduces the level of dimeric polyphenols in beer (Table 14.10). Nevertheless commercial beers contain 0 5-4-0 mg/1 and one experimental beer contained 22-0 mg/1 of procyanidin B-3 [53]. 

PRACTICAL ASPECTS OF IMPROVING BEER STABILITY As discussed above the presence of complex proteins and polymerized polyphenols in beer is likely to lead to haze formation. Conversely, the removal of part of either group of macromolecules is likely to improve beer stability. However, it is neither practical nor desirable to remove all of... 

McMurrough I, Madigan D, Kelly RJ, Smyth MR (1996) The role of flavonoid polyphenols in beer stability. J Am Soc Brew Chem 54 141-148... 

ElKaoutit M, Naranjo-Rodriguez 1, Temsamani KR, De La Vega MD, De Cisneros JLHH (2007) Dual laccase - tyrosinase based sonogel-carbon biosensor for monitoring polyphenols in beers. J Agric Food Chem 55(20) 8011-8018... 

There has been some evidence of a higher antioxidant effect when both flavonoids and a-tocopherol are present in systems like LDL, low-density lipoproteins (Jia et al., 1998 Zhu et al, 1999). LDL will incorporate a-tocopherol, while flavonoids will be present on the outside in the aqueous surroundings. A similar distribution is to be expected for oil-in-water emulsion type foods. In the aqueous environment, the rate of the inhibition reaction for the flavonoid is low due to hydrogen bonding and the flavonoid will not behave as a chain-breaking antioxidant. Likewise, in beer, none of the polyphenols present in barley showed any protective effect on radical processes involved in beer staling, which is an oxidative process (Andersen et al, 2000). The polyphenols have, however, been found to act synergistically... 

ANDERSEN M L and SKIBSTED L H (2001) Modification of the levels of polyphenols in wort and beer by addition of hexamethylenetetramine of sulfite during mashing, J Agric Food Chem, 49, 5232-7. 

A similar problem occurs with beer stabilization. A serious problem in the brewing industry is the tendency of some beers to develop hazes during long-term storage due to protein precipitation that is usually stimulated by small quantities of naturally occurring proanthocyanidin polyphenols. In the same way as observed for wine, the excess polyphenols are traditionally removed by treatment with insoluble PVPP, with the same resulting problems. To resolve the problems, several authors have proposed the use of laccase, which forms polyphenol complexes that may be removed by filtration or other separation means. 

DF content in the beverages listed in Table 8.4 ranges from 0.2 to 1.7 g/liter. These DFs contain an appreciable amount of associated phenolic compounds (from 0.05 to 0.89 g/liter). The main polyphenols associated with DF in wine are flavan-3-ols and benzoic acids (Saura-Calixto and Diaz-Rubio 2007), whereas in beer there would be flavonoids, followed by hydroxycinnamic acids linked to arabinoxylans (Dfaz-Rubio 2008). 

The time course of protein-polyphenol haze development in many packaged clear beverages has a two-phase pattern (see, for example, Fig. 2.17). At first no observable change occurs for some time. After this, haze formation begins and follows an essentially linear development rate. This phenomenon has been reported in beer (McMurrough et al., 1992) as well as apple juice, grape juice, and cranberry juice cocktail (Siebert, 1999, 2006). 

A variation on the Thompson and Forward method was developed in which a HA peptide or peptide-like material (e.g., gelatin, gliadin, polyproline, or soluble polyvinylpyrrolidone) is added to a sample to induce haze in proportion to the amount of HA polyphenol it contains (Siebert et al., 1996a). This gives little response in beer, which contains very little HA polyphenol, and causes much larger haze increases in fruit juices and wine. 

Adsorbents that remove proteins or polyphenols are used to treat a number of beverages to delay the onset of haze formation. Protein adsorbents include bentonite and silica. Bentonite removes protein nonspecifically (see Fig. 2.19) and so is unsuitable for stabilizing beverages where foam is desirable (beer and champagne). Silica, on the other hand, has remarkable specificity for HA proteins while virtually sparing foam-active proteins in beer (Siebert and Lynn, 1997b) (see Fig. 2.20). Silica removes approximately 80% of the HA protein from unstabilized beer, while leaving foam-active protein nearly untouched at commercial treatment levels. 

Eastmond, R. and Gardner, R. J. (1974). Effect of various polyphenols on the rate of haze formation in beer. J. Inst. Brew. 80,192-200. 

The taste-tests yielded positive results, although in beers produced using polyphenol-free CC>2-extracts a somewhat less full-bodied note, with equivalent bitterness, was found. This... 

Protein haze in white wine thus differs in several aspects from protein haze in beer. It is well established that beer protein haze is due to interactions between proteins, derived from the barley storage protein hordein and rich in proline, and hop polyphenolic compounds (Bamforth 1999 Miedl et al. 2005 Siebert 1999 Siebert and Lynn 2003). White wine proteins are not derived from storage proteins of grape seed nor are they as rich in proline as hordein. In addition, wine protein haze formation cannot be eliminated by removing polyphenolic compounds by PVPP (Pocock et al. 2006) while in beer this has been applied as a commercial strategy (Leiper et al. 2005 Madigan et al. 2000). 

Even people who have been taking blood pressure-lowering drugs will benefit from this natural choice. And individuals who are determined to get their blood pressure down without drugs will benefit enormously. Tomato extract, which is rich in the antioxidant polyphenols lycopene, phytoene, and phytofluene, has been shown to reduce blood pressure for treated but not completely controlled hypertensive individuals, as well as for never-treated men and women in the category of prehypertension. Two studies have been done at the University of the Negev in Beer Sheva, Israel, by Dr. Esther Paran and her colleagues. 

The majority of the nitrogen compounds in beer have molecular weights between 5 and 70 kDa. The protein components of this fraction are of particular importance in brewing, as some of them contribute to foam formation (positive effect) while others, in association with polyphenols, lead to haze formation (undesirable effect) [10]. 

Beer contains a mixture of phenolic compounds, averaging about 150-350 mg/L, out of which about two thirds originate in barley and the remaining in hops [11]. Of these, polyphenols present the greatest interest for beer processing and storage, since they tend to associate with proteins into insoluble complexes, leading to the formation of cold haze in beer. 

Haze formation is mostly attributed to proteins, polyphenols, and their interactions. It is also possible that there are also other factors that inbuence haze formation in beer, but their effect has not been yet clearly debned [ 15]. The amount of haze formed depends both on the concentration of proteins and polyphenols, and on their ratio. Polyphenols can combine with proteins to form colloidal suspensions that scatter light, which creates the cloudy appearance of beer. Beer polyphenols originate partly from barley and partly from hops. The beer polyphenols most closely associated with haze formation are the proanthocyanidins, which are dimers and trimers of catechin, epicatechin, and gaUocatechin. These have been shown to interact strongly with haze-active proteins [13,15-17] and their concentration in beer was directly related to the rate of haze formation [18]. Ahrenst-Larsen and Erdal [19] have demonstrated that anthocyanogen-free barley produces beer that is extremely resistant to haze formation, without any stabilizing treatment, provided that hops do not contribute polyphenols either. Not all proteins are equally involved in haze formation. It has been shown that haze-active proteins contain signibcant amounts of proline and that proteins that lack proline form little or no haze in the presence of polyphenols [13,15-17]. In beer, the source of the haze-active protein has been shown to be the barley hordein, an alcohol-soluble protein rich in proUne [16]. 

The nature of the other bittering principles in beei brewed from old hops is still largely unknown. These substances probably contain more oxygen than the iso-a-acids, are more polar, and incompletely extracted into isooctane. The abeo- %o-aL-2iC ds (p. 487) are such compounds, the concentration of which in lager beers was reported to be 88-160 mg/1. Subsequent work established the presence of polyphenols in the extracts analysed and found that the concentration of f6 o-iso-a-acids in English beers was less than 6 ppm [57]. Many other oxidation products of the hop resins have been detected in beers (see Chapter 12) but in most cases it has not been established that they are normal constituents. 

In addition to proteins, polyphenols, and metallic ions, hazes contain 2-4% of glucose and traces of the pentoses, arabinose and xylose [162]. Occasionally, however, hazes are encountered which are essentially different from the protein-polyphenol hazes discussed so far. These include hazes due to microcrystals of calcium oxalate (the solubility of which is 6 07 mg/1 at 13°C) and hazes which are composed largely of carbohydrates. a-Glucans (dextrins) [170], p-glucans [171] and pentosans [172] have been found in beer sediments. 

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