Tannins are plant natural products that have molecular weights of at least 500 g/mol, that have more than one phenolic moiety, and that form stable complexes with proteins. Tannins are constituents of the larger class of plant products known as polyphenolics, but tannins are unique in their ability to precipitate proteins. They are also potent antioxidants and chelate metals such as iron or copper. We are interested in the bioactivities of tannins found in the human diet (tea, wine, chocolate, fruits) and in the ecological significance of tannins found in natural systems (soils, herbivory). In particular, we use purified tannins to establish structure-activity relationships with the long term goal of understanding of tannins as individual bioactive compounds.
In the diagram above, the precipitation data shows that green tea polyphenol epigallocatechin gallate (EGCg) does not precipitate protein efficiently compared to condensed tannin procyanidin (PC) or gallotannin pentagalloyl glucose (PGG). However, EGCg binds selectively to the hydrophobic pocket of serum albumin (right). Binding to serum albumin stabilizes EGCg for transit through the blood and modulates albumin-related properties such as tendency to form glycated adducts under conditions of high blood sugar (diabetes). Our tools to probe selective interaction range from fluorescence spectroscopy to MALDI-TOF mass spectrometry.
Many of the analytical tools that we use can be found in the Tannin Handbook (see menu tab).