Proanthocyanidins sample fractionation

A major drawback of all functional group assays is that a satisfactory standard does not exist. For a given sample the most appropriate standard is a purified procyanidin fraction prepared from the same matrix. The isolation and characterization of such purified fractions are laborious. Added to that procyanidins undergo oxidation, complexation and self-polymerization very easily, rendering such purified fractions only reproducible to a limited degree. At least in the proanthocyanidin assay the color reaction depends not only on the polyphenols themselves, but also on the matrix. The use of specified proanthocyanidins as a standard in a suitable blank matrix is an attempt to correct for such effects [67],... 

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