Reactivity
The construction of models that would accurately predict the effects of tannins on biological systems is difficult, mainly due to the enormous structural variations among them. However they undergo specific reactions with the following:
- Proteins
- Carbohydrates
- Metals
1) Proteins
Tannin-protein interactions are specific and depend on the structure of both the protein and tannin. Protein characteristics that favour strong bonding are large molecular size, open and flexible structures and richness in proline. In addition their interaction has been found to be influenced by temperature, pH, solvent composition and tannin:protein ratio. The most important tannin-protein interaction is the one leading to the transformation of animal skin to leather (tanning).
2) Carbohydrates
Starch has the ability to form hydrophic cavities that facilitate the embedding of tannins. Other less well understood interactions are with cellulose and cell wall carbohydrates. Tannin-carbohydrate interactions are increased by using carbohydrates with higher molecular weight, open and flexible structures and low solubility. These interactions are probably based on hydrophylic and hydrogen linkages.
3) Metals
Tannins can be metal ion chelators.The complexes formed are often coloured, and it has been suggested that characteristic colours can be used to identify specific arreangements of the phenolic groups in tannins. Metal ion chelation can alter the redox potential of the metal, or prevent its partecipation in redox reactions (e.g. oxidation leading to cancer).
Home Occurrence Structure Reactivity