Tannin/protein ratio

This does not seem to occur in all cases. Some authors have observed that with an increase in tannin/protein ratio there is the formation of large particles that eventually precipitate. A three-phase model has been proposed to explain this phenomenon [33, 51]. The simultaneous binding of the multidentate tannin to several places in the protein leads to the protein wrapping around the tannins. As the concentration of tannin increases, several tannin molecules bind to the protein surface and crosslink with other proteins, leading to protein association. As more tannin is added, more protein-tannin complexes aggregate, forming larger particles that precipitate. 

Tannins have been shown to retard markedly the decomposition of organic substances. Basaraba and Starkey (1966) observed that chestnut and wattle tannins formed complexes with gelatin and gliadin and thereby reduced the rate of decomposition of the proteins. The effect of tannin on the decomposition of peptone and an amino acid was much less. Similar studies by Benoit and Starkey (1968) with wattle tannin and various enzymes also showed marked inhibition. Urease was almost completely inactivated when the tannin—urease ratio was 1/10, whereas for a similar degree of inactivation a ratio of... 

The affinity of tannins to bind proteins is favored by their ability to work as multidentate ligands (cross-linking) in which one tannin is able to bind to more than one protein at one time (Fig. 9D.llb) or to bind to more than one point in the same protein (Charlton et al. 2002a Siebert et al. 1996). These associations between tannin and protein could result in aggregates that precipitate depending on the ratio of protein/tannin and also the concentration of protein (Frazier et al. 2003 Poncet-Legrand et al. 2006). 

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