Tannin-anthocyanin interactions

Tannin-Anthocyanin Interactions Influence on Wine Color... 

Tannin and anthocyanin interaction were studied by UV-Visible spectrometry to understand both copigmentation phenomenon and polymerization reactions. The aim of the work was to conduct studies in wine like model solution (pH... 

The astringency of wine tannin fractions appears to be correlated to the content of flavanol units released after thiolysis regardless of their environment in the original mol-ecules. Anthocyanins contributed neither bitterness nor astringency. Whether incorporation of anthocyanin moieties in tannin-derived structures affects their interactions with proteins and taste properties remains to be investigated. 

Flavanol oligomers and polymers are also called condensed tannins or proan-thocyanidins. The term tannin refers to their capacity to interact or react with proteins and precipitate them out. When heated under acidic conditions, these molecules release red anthocyanidin pigments, hence the term proanthocyanidins. The term leucoanthocyanidin, also referring to this particular property, is sometimes encountered in the literature. However, this should be restricted to another group of compounds, flavan 3,4-diols, which are intermediates in the biosynthetic pathway leading to flavanols and anthocyanins (Stafford and Lester 1984 Nakajima et al. 2001 Abrahams et al. 2003) but have never been isolated from grapes, presumably due to their instability. 

Despite these advances, it is generally accepted that the vast majority of die observed color in aged red wine remains to be characterized. The obvious factor that separates characterized compounds from uncharacterized compounds appears to be molecular weight, with much of the high molecular weight material being unknown in structure. What is apparent is that as wine ages, the observed red color increases in size, apparently due to interaction between anthocyanins and proanthocyanidins (tannin) (10). 

Singleton, V.L. Trousdale, E. Anthocyanin-tannin interactions explaining differences in polymeric phenols between white and red wines. Am. J. Enol. Vitic. 1992,43, 63—70. 

The solvent extraction is the most used method for phenolic compoimds obtainment from plant tissue. The main factor is the phenolics solubility, which depends on its chemical structure. Plant materials may contain different concentrations of phenolic acids, phenylpropanoids, anthocyanins and tannins. It is possible to occur interactions between phenolics and other plant components, such as carbohydrates and proteins which form complexes responsible for insolubility. Besides that, the polarity of solvent affects the solubility and therefore, it is eonsidered difficult to develop a extraction method suitable for all plant phenolics [18]. 

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