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≥95.0% of proanthocyanidins by spectrophotometry
Proanthocyanidins, also known as condensed tannins, are products formed from the condensation of flavan-3-ol units. Depending on the number of condensed flavan-3-ol units (up to 10 or more) they are divided into Oligomeric Proanthocyanidins (OPC) or Polymeric Proanthocyanidins (PPC). According to the number of bonds that link the flavan units, Proanthocyanidins are further classified as A-type (twofold bond), or B-type (single bond). Grape seeds Proanthocyanidins are mostly B-type.
Due to their stereochemical complexity and the number of different isomers that can be generated during the formation of the interflavane link, the structure of Proanthocyanidins is poorly known, except for the lower terms (dimer to tetramers). Proanthocyanidins mixtures are characterized by the ratio between flavane monomers, lower oligomeric and higher oligomeric constituents.