Add time:09/02/2019         Source:sciencedirect.com

The present knowledge on the qualitative and quantitative analysis of procyanidins is reviewed. Procyanidins belong to the class of natural products known as proanthocyanidins or condensed polyphenols. The instability of procyanidins should be considered throughout sample collection, storage and clean up procedures. Extractions are preferentially conducted using aqueous acetone. Addition of an antioxidant is recommended as long as it does not interfere with the analytical procedure. Conventional methods are mainly based on color reactions, of which only functional group assays exhibit specificity for proanthocyanidins. The dimethylaminocinnamaldehyde assay is gaining importance compared to the most widely used vanillin assay, because it is more specific, more sensitive and less subject to interferences. Individual procyanidins can only be assessed by chromatography. Reversed phase high performance liquid chromatography on C-18 stationary phases using acidic aqueous methanol or acetonitrile as eluents is the procedure of choice. Oligomeric procyanidins do not elute according to their degree of polymerization. Polymers can not be chromatographed and hamper the most commonly used UV detection at 280 nm. Sample clean up procedures are inevitable because of these polymeric compounds and phenolic acids as well as flavonoids, which tend to co-elute with procyanidins. Liquid 1 quid extraction using ethyl acetate is not quantitative. Solid phase extraction over C-18, polyamide or Sephadex LH-20 are described in the literature, but none of these procedures is completely validated. More selective detection modes like electrochemical detection or mass spectrometry as well as derivatization procedures are discussed as possible alternatives to extensive sample clean up procedures.

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