Model reactions with tannins

Figure 5. Correlation of loss of malvidin-3-glucoside (MSG) with pigmented polymer formation in model reactions with anthocyanins, tannins, acetaldef de...

Drawing on this and the reported specificity of tannin-protein interactions ( ) leads to the conclusion that any useful in vitro modelling of the impact of tannins on digestion must consider more than pH and the concentrations of the buffer, enzyme, substrate, and tannin. The actual enzyme-substrate system must be nutritionally realistic to control for specificities of the reaction of tannins with proteins (including enzymes) gastrointestinal mucoproteins should perhaps also be included on the same grounds. Besides all this, misleading results nay still be obtained if bile surfactants are omitted from the equation. 

Reactions of Tannin Model Compounds with Methylolphenols... 

While the identity of the relevant yeast metabolites in the fermented medium sampled at day 2 needs to be clarified, previously published data have provided some evidence about the role of acetaldehyde-mediated condensation of catechin with MSG (13-20). We therefore aimed to extend these model studies and to confirm chemical formation of pigmented polymers from condensed tannins, which are commercially used in red winemaking, and anthocyanins. The model reactions were conducted with vatying concentrations of acetaldehyde and SO2 as shown in Table 2 and analysed by HPLC after 2, 4 and 7 days. After 7 days visible precipitation of unidentified material started to occur in presence of acetaldehyde and the reactions were discontinued. 

Foo L Y, Hemingway R W 1985 Condensed tannins Reactions of model compounds with fur-furyl alcohol and furfuraldehyde. J Wood Chem Technol 5 135-158... 

In conclusion, flavanols, procyanidins and, consequently, condensed tannins react more-or-less easily with free radicals, according to their configuration. These chain reactions produce brown polymers with varying structures that precipitate. In wine, these phenomena depend on the phenol content. The oxidation kinetics are apparently slower than in a model medium, probably due to the presence of even more easily oxidizable compounds, also involved in the oxidation of procyanidins. 

The taste and mouthfeel properties of three different types of tannin-like polyphenolic compounds, representative of some of the tannin-like polyphenolic compounds found in red wines, were determined using descriptive sensory analysis [50]. Ethyl-bridged fiavan-3-ols were produced by reaction of (+)-catechin with acetaldehyde under acidic conditions. Red-colored tannin-like polyphenolic compounds from wine and from wine pomace were isolated by multilayer coil countercurrent chromatography (MLCCC). Mouthfeel attributes and bitterness of the fractions dissolved in a model wine (MW) medium were rated while the fractions were held in the mouth and after expectoration. The sensory properties... 

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