Protein-polyphenol tannin interactions

Polyphenols (tannins) form reversible, and often insoluble, complexes with proteins. The principal mechanisms of polyphenol-protein binding are thought to be (i) hydrogen bonding (ii) hydrophobic interactions (iii) ionic interactions. Our current knowledge of the structure of plant polyphenols is sufficient to eliminate (iii). The thrust of recent studies has been to try and define the relative balance between (i) and (ii) for polyphenol complexation with proteins, carbohydrates, and organic bases (the three phenomena being very closely linked). 

The model of interactions between tannins and proteins (Figure 6.22) described by Haslam in 1981 is still in use today. In the case of small quantities of proteins, the polyphenols spread over the surface in a single layer, thus decreasing their hydrophilic character. The proteins clump together and, eventually, precipitate. When the protein concentration increases, phenolic compounds spread over their surface act as ligands or cross-linking agents between the various molecules. The superficial hydrophobic layer then recombines and causes the proteins to precipitate. Therefore, the relative concentrations of tannins and proteins affect the formation and precipitation of tannin-protein complexes. 

Three-dimensional structure and dynamics of wine tannin-saliva protein complexes. A multitechnique approach. Biochemistry 42 10385-10395 Haslam E (1974) Polyphenol-protein interactions. Biochem J 139 285 Jobstl E, Howse JR, Fairclough JPA, Williamson MP (2006) Noncovalent cross-linking of casein by epigallocatechin gallate characterized by single molecule force microscopy. J Agric Food Chem 54 4077 081... 

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