Structure and Chemical Properties of the Condensed Tannins

Abstract

The condensed tannins are oligomers and polymers ofpolyhydroxyflavan-3-01 monomer units linked by acid-labile 4 -+ 6 or 4 -+ 8 bonds. The polymers are polydisperse, and the chains are irregular, sometimes bran-ched, and often contain more than one type of configurational base unit. Condensed tannins are relatively unstable in aqueous solution and dis-proportionate in mild acids or bases. The monomer units extensively rearrange in stronger acidic or basic solutions. The reactions are largely radical-mediated in basic solutions to form highly rearranged and ox-idatively coupled products. Condensed tannins complex strongly with metal ions, carbohydrates, and proteins.