Proanthocyanidin condensed tannins

The proanthocyanidin assay is carried out in a solution of butanol-concentrated hydrochloric acid, where proanthocyanidins (condensed tannins) are converted to antho-cyanidins (products of autoxidation of carbocations formed by cleavage of interfla-vanoid bonds) (Matus-Cadiz and others 2008). 

Butler LG, Price ML, Brotherton JE (1982) VaniUin assay for proanthocyanidins (condensed tannins) modification of the solvent for estimation of the degree of polymerization. J Agric Food Chem 30 1087-1089... 

According to some studies, the compounds form as reaction by-products between anthocyanins and flavan-3-ols, such as catechins and proanthocyanidins (condensed tannins). These reactions may also involve other molecules such as acetaldehyde, pyruvic acid, acetoacetic acid, vinylphenol, vinylguaiacol, vinylcatechol, and dimerization of anthocyanins (Asenstorfer et ah, 2001 Atanasova et al., 2002 Bakker and Timberlake, 1997 Brouillard and Dangles, 1994 Fulcrand et ah, 1996, 1998 He et al., 2006 Liao et ah, 1992 Remy et ah, 2000 Salas et ah, 2004 Schwarz et al., 2003 Timberlake and Bridle, 1976). 

Among polyphenolic compounds, two types of flavonoids, the anthocyanins and flavanols (i.e., catechins, proanthocyanidins, condensed tannins), are particularly relevant to the quality of red wines, as they are key compounds for color definition and astringency. Other flavonoids such as flavonols may have some influence on color and bitterness, although they are present in red wines in much lower amounts. Phenolic acids and hydrolysable tannins, released from barrel wood, may also have an influence on wine taste and color, and hydroxycinnamoyl derivatives from grape must are involved in the oxidative browning of white wines together with flavanols. Besides, some of these perceptions may be modified by other sensory characteristics (e.g. sourness, sweetness) related to other wine components (Preys et al. 2006). 

Fig, 5.2. Biosynthesis of flavonoids and proanthocyanidins (condensed tannins). Enzymes in bold have been cloned from P. tremuloides and show induction by herbivory (Peters and Constabel, 2002 R. Mellway and C. P. Constabel, unpublished data). Abbreviations are as follows Phe, phenylalanine PAL, phenylalanine ammonia lyase 4CL, 4-coumarate CoA Ligase CHS, chalcone synthase CHI, chalcone isomerase F3H, flavanone 3-hydroxylase FLS, flavonol synthase DFR,... 

The potential of this development for the structural elucidation of the proanthocyanidin condensed tannins, especially the 5-deoxy analogues, from important commercial sources is clear. In addition, the method facilitates the ready definition of the absolute configuration of the chainterminating flavan-3-ol moiety in 5-deoxyoligoflavanoids, especially in... 

The term tannins also attributed to proanthocyanidins (condensed tannins) was defined by Bate-Smith and Swain in 1962 as water soluble phenolic compounds having molecular weights between 500 and 3,000 Da and, besides giving the usual phenolic reactions, they have special properties such as the ability to precipitate alkaloids, gelatine and other proteins. Tannins have been widely employed in the tanning process converting hide collagen in leather [292]. 

Several methods have been described in the literature to quantify proanthocyanidins (condensed tannins) however, the most common are the acid-butanol assay and vanillin assay. 

Gessner MO, Steiner D (2005) Acid butanol assay for proanthocyanidins (condensed tannins). In Gra9a MAS, Barlocher F, Gessner MO (eds) Methods to study litter decomposition a practical guide. Springer, Netherlands... 

Hydrolysable tannins ( HTs ) are, with the proanthocyanidins ( condensed tannins ), one of the two principal classes of tannins. 

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