However, another explanation is that this association is merely an artifact of tannin isolation from non-living cells. Indeed, the location of tannins and cell wall carbohydrates is quite different in living cells than in plant cells after digestion by animals. Tannin-carbohydrate interactions are increased by carbohydrates with high molecular weight, low solubility and conformational flexibility. These interactions are probably based on hydrophobic and hydrogen linkages. The capacity of tannins to bind proteins has been recognized for centuries.
Leather tanning is a very ancient practice.
Tannin-protein interactions are specific and depend on the structure of both the protein and tannin. Protein characteristics that favor strong bonding large molecular size, open and flexible structures, richness in proline. Tannin characteristics that favor strong bonding high molecular weight, high conformational mobility. Chemical linkages Tannin-protein interactions are most frequently based on hydrophobic and hydrogen bonding. Ionic and covalent bonding occur less frequently.