Polyphenol interactions with proteins

Siebert, K. J. and Lynn, P. Y. (1998). Comparison of polyphenol interactions with PVPP and haze-active protein. ]. Am. Soc. Brew. Chem. 56, 24431. 

Flavonoids and other polyphenols can interact with lipids and proteins. The interactions with proteins could be both unspecific or specific, meanwhile the interactions with lipids seems to be rather unspecific, based essentially on physical adsorption. This physical adsorption would mostly depend on the hydrophobic/hydrophilic characteristics of the flavonoid molecule, the number of hydroxyl substituents, and the polymerization degree [Erlejman et al., 2004 Verstraeten et al., 2005, 2003, 2004]. 

Many polyphenols have the property of interacting with proteins, mainly through hydrophobic interactions and formation of hydrogen bonds. " This property accounts for a third antioxidant mechanism. Some polyphenols have been shown to inhibit ROS-generating enzymes like xanthine oxidase, cyclo-oxygenase, or Upo-oxygenase, by complexing the enzyme. 

Siebert, K.J. Lynn, P.Y. Comparison of polyphenol interactions with polyvinylpolypyr-rolidone and haze-active protein. J. Amer. Soc. Brewing Chem. 1998, 56, 24-31. 

The role of protein-polyphenol interactions with regard to the development of non-biological haze is discussed further in Chapter 22 together with the methods employed to inhibit these reactions and prolong the shelf-life of bottled beer. 

Polyphenols (tannins) form reversible, and often insoluble, complexes with proteins. The principal mechanisms of polyphenol-protein binding are thought to be (i) hydrogen bonding (ii) hydrophobic interactions (iii) ionic interactions. Our current knowledge of the structure of plant polyphenols is sufficient to eliminate (iii). The thrust of recent studies has been to try and define the relative balance between (i) and (ii) for polyphenol complexation with proteins, carbohydrates, and organic bases (the three phenomena being very closely linked). 

Another molecular mode of action of furanocoumarins is related with protein modification. Proteins have multiple functions enzymes, transporters, ion channels, receptors, microtubules, structural proteins, etc. Conformational changes alter their properties and can prevent effective cross talk between proteins themselves and between proteins and other targets. Polyphenols can interact with proteins by forming hydrogen bonds and ionic bonds with electronegative atoms of the peptide bond or the positively charged side chains of basic amino acids, respectively. 

The crospovidones are easily compressed when anhydrous but readily regain their form upon exposure to moisture. This is an ideal situation for use in pharmaceutical tablet disintegration and they have found commercial appHcation in this technology. PVP strongly interacts with polyphenols, the crospovidones can readily remove them from beer, preventing subsequent interaction with beer proteins and the resulting formation of haze. The resin can be recovered and regenerated with dilute caustic. 

McManus, J.P. et ak. Polyphenol interactions. Part 1. Introduction some observations on the reversible complexation of polyphenols with proteins and polysaccharides. J. Chem. Soc. Perkin Trans. II1429, 1985. 

Studies of the association of polyphenols with proteins have a long history (27). Loomis (28) has succinctly summarised the conclusions of this earlier work. The principal means whereby proteins and polyphenols are thought to reversibly complex with one another are (i) hydrogen bonding, (ii) ionic interactions and (iii) hydrophobic interactions. Whilst the major thrust in earlier work was to emphasize the part played by intermolecular hydrogen bonding in the complexation, Hoff (29) has drawn attention to the possibility that hydrophobic effects may dominate the association between the two species. 

This chapter deals with the Maillard reaction, the oxidation of sulfur-containing amino acids, isopeptide bonds, alkaline treatments, the interaction of proteins with polyphenols, and the oxidation and heat treatment of tryptophan. 

Many of the wine macro-components (e.g. carbohydrates, proteins, polyphenols), come from the skins and the pulp of grapes and from the cell walls of the yeast. Although this varies, the molecular weight of the majority of macromolecules is over 10,000 D and their final concentration ranges from 0.3 to 1 g/L (Voilley et al. 1991). Most macromolecules will be eliminated by clarification and stabilization treatments of the wine. Because of their interactions with wine aroma... 

Poncet-Legrand, C., Edelmann, A., Putaux, J.-L., Cartalade, D., Sarni-Manchado, R, Vernhet, A. (2006). Poly(L-proline) interactions with flavan-3-ols units Influence of the molecular structure and the polyphenol/protein ratio. Food Hydrocolloids, 20, 687-697. 

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]. 

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