Sample preparation proanthocyanidins

For the red wines (82-84), which were injected directly into the HPLC without sample preparation, a ternary-gradient system using aqueous acetic acid (1% and 5% or 6%), and acidified acetonitrile (acetonitrile-acetic acid-water, 30 5 6) was used for cinnamic acid derivatives, catechins, flavonols, flavonol glycosides, and proanthocyanidins. Due to the large number of peaks, the gradient was extended to 150 min for the resolution of many peaks of important phenolics. This direct injection method was able to separate phenolic acids and esters, catechins, proanthocyanidins, flavonols, flavonol glycosides, and other compounds (such as tyrosol, and rrans-resveratrol) in wine in a single analysis. However, use of acetic acid did not permit the detector (PDA) to be used to record the UV spectra of phenolics below 240 nm (84). 

Sample Preparation for Determination of the Mean Polymerization Degree (mDP) of Proanthocyanidins in Skins and Seeds Extracts and in the Wine... 

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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