Tannins polymerization

Fig. 6.26. Example of tannin polymerization (a) organized polymerization of tannins, an example of a tetrameric procyanidin (b) disorganized polymerization of tannins (reactions with free radicals) (Glavin, 1993)...

Polymers -676 -l- condensed tannins Polymerized procyanidins + tannin-polysaccharides -350 to -900... 

In addition to the molecnlar strnctnre, the tan-nin/anthocyanin ratio also affects wine development. Color has been observed to change rapidly due to anthocyanin breakdown reactions when the medinm has a low tannin content (molar ratio T/A tannin concentration is much higher than the anthocyanin content (molar ratio T j A < 4). If a wine is to develop harmoniously, this ratio should be between 1 and 4, i.e. 500 mg of anthocyanins and 1-3 g of tannins per liter of wine. 

NR blended with condensed tannin (polymeric proanthocyanidins) formed semi-IPN composites by haematin-catalysed crosslinking. ... 

Tannins are polyhydroxyphenols. They are soluble in water, aleohols and aeetone and ean eoagulate proteins. They are yielded by extraetion from wood substanee, bark, leaves and fruits. Other components of the extraction solutions are sugars, pectins and other polymeric carbohydrates, amino acids and other substances. The content of non-tannins can reduce wood failure and water resistance of glued bonds. The polymeric carbohydrates especially increase the viscosity of the extracts. 

Tannin chemistry is complex and tannin blends (composed of singletree species tannins mixed together) offer a number of useful water treatment functions. Apart from oxygen-scavenging abilities, they act as passivating agents, film-formers, sequestrants, and polymeric sludge dispersants (for more details, see Section 10.3). 

Tannins are typically used in BW at 150 to 200 ppm active tannin product, but perhaps only a third of this is related to its polymeric sludge conditioning functionality. 

Tannins may be found bound up with magnetite in waterside tube deposits. Degradation products of amines, glycols, polymeric dispersants, chelants, and other organics may also be found and usually are reported in the deposit analysis as a loss on ignition. 

CZE is particularly useful for separating anthocyanin dimers or polymeric anthocyanins. Calvo et al. (2004)" separated 13 anthocyanins by CZE including acylated and non-acylated anthocyanins, pyranoanthocyanins, and flavonol derivatives in wine. Saenz-Lopez et al. (2004)" applied CZE to analyze wine aging (1 to 14 yr) as related to monomeric anthocyanins, anthocyanin derivatives, tannins, and fla-vonols. Bicard et al. (1999)" reported the improved detection sensitivity of anthocyanin chemical degradation analysis by CZE. 

Flavan-3-ols orflavanols have a saturated three-carbon chain with a hydroxyl group in the C3 position. In foods they are present as monomers or as proanthocyanidins, which are polymeric flavanols (4 to 11 units) known also as condensed tannins. In foods they are never glycosylated. 

Proanthocyanidins (PAs), also known as condensed tannins, are oligomeric and polymeric flavan-3-ols. Procyanidins are the main PAs in foods however, prodelphinidins and propelargonidins have also been identified (Gu and others 2004). The main food sources of total PAs are cinnamon, 8084 mg/100 g FW, and sorghum, 3937 mg/100 g FW. Other important sources of PAs are beans, red wine, nuts, and chocolate, their content ranging between 180 and 300 mg/100 g FW. In fruits, berries and plums are the major sources, with 213.6 and 199.9 mg/100 g FW, respectively. Apples and grapes are intermediate sources of PAs (60 to 90 mg/100 g FW), and the content of PAs in other fruits is less than 40 mg/100 g FW. In the majority of vegetables PAs are not detected, but they can be found in small concentrations in Indian squash (14.8 mg/ 100 g FW) (Gu and others, 2004 US Department of Agriculture, 2004). 

Tannins, like lignins, are polymerized phenolics with defensive properties. Their name comes from their use in tanning rawhides to produce leather. In tanning, collagen... 

There are two categories of tannins condensed and hydrolyzable tannins. The polymerization of flavonoid molecules produces condensed tannins, which are commonly found in woody plants (Fig. 3.9). Hydrolyzable tannins are also polymers, but they are a more heterogeneous mixture of phenolic acids (especially gallic acid) and simple sugars. Though widely distributed, their highest concentration is in the bark and galls of oaks. 

Flavanols and procyanidins Flavanols, or flavan-3-ols, are synthesized via two routes, with (+) catechins formed from flavan-3,4-diols via leucoanthocyanidin reductase (LAR), and (—) epicatechins from anthocyanidins via anthocyanidin reductase (ANR) (see Fig. 5.4). These flavan-3-ol molecules are then polymerized to condensed tannins (proanthocyanidins or procyanidins), widely varying in the number and nature of their component monomers and linkages (Aron and Kennedy 2008 Deluc and others 2008). It is still not known whether these polymerization reactions happen spontaneously, are enzyme catalyzed, or result from a mixture of both. 

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... 

Some animals process plants to reduce defense compounds even before eating. The meadow vole M. pennsylvanicus cuts winter branches of white spruce, Norway spruce, white pine, and Norway pine and leaves them on the snow for 2-3 days before eating them. This reduces the levels of condensed tannins and other phenolics by one half, to their summer levels. A high level of protein 12%) and reduced phenolics (1.5% of dry matter) now render the food acceptable. It is not clear how the phenolics are being lost, possibly by polymerization or oxidation (Roy and Bergeron, 1990b). 

The second group of tannins are the condensed tannins, or polymeric proanthocyanidins (2). These are composed offlavonoid units, and are more recalcitrant to biodegradation than hydrolysable tannins. Of these, the... 

The PAs, or condensed tannins, are polymers synthesized from flavan-3-ol monomer units. The phlobaphenes are 3-deoxy-PAs formed from flavan-4-ol monomers. The biosynthesis of both types of PAs follows the biosynthetic route of anthocyanins from chalcones through to the branch points to flavan-3-ol and flavan-4-ol formation. In this section, the specific enzymes forming the monomers are discussed, along with a discussion on the polymerization process. Although the chemistry of tannins is described in detail elsewhere in this book, it is useful to briefly mention the nature of the monomer subunit types and the polymer forms. 

Yoneda, S., Kawamoto, H., and Nakatsubo, F., Synthesis of high molecular mass condensed tannins by cationic polymerization of flavan-3,4-carbonate, J. Chem. Soc., Perkin Trans. 1, 1025, 1997. 

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