Analysis of Catechins and Procyanidins

Due to the relatively low levels of these compounds in the grape skins, direct analysis of the extract usually does not provide sufficient sensibility. As a consequence, prior to analysis it is necessary to concentrate the sample by passage through a C18 cartridge. Five millilitres of 

HPLC analysis can be performed by direct injection of the tartrate buffer extract. The chromatographic peaks of catechin and epicatechin are well resolved, but an overlapping of procyanidins and epicatechin gallate with other compounds, may occur. To improve the separation among them, a fractionation of the sample on a C18 cartridge can be performed 5 mL of extract are added of 15 mL H2S04 5 x 10 3M and passed 

Determination of the mean polymerization degree (mDP) of proanthocyanidins in skins and seeds extracts and in the wine 

To perform analysis of proanthocyanidins after thiolysis with benzyl mercaptan (see paragraph 2.3.2) a C18 column similar to that described above operating at temperature of 45 °C, can be used. Before injection, the methanol content of the solution is reduced to 20% (v/v) by adding water to minimize peak tailing. As mobile phase, a binary solvent 

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Table 2.9 HPLC gradient program used for analysis of catechins and procyanidins dimer in the skins extract by C18 (250 x4mm, 5 pm) column (flow rate 0.5mL/min).

Figures 2.21,2.22 and 2.23 show the chromatograms relative to analysis of catechins and procyanidins prior to fractionation in the cartridge, of catechins monomer (fraction diethyl ether) and of procyanidins dimer (fraction ethyl acetate), respectively. As evidenced by Figures 2.20 and 2.23, the main procyanidin in seeds is procyanidin B2, however in skins procyanidin Bl prevails.

Figure 2.21 Chromatogram relative to analysis of catechins and procyanidins in the seeds extract prior fractionation on the C18 cartridge (sample volume injected 10pL). 1. procyanidin Bl, 2. procyanidin B3, 3. (+)-catechin, 4. procyanidin B4, 5. procyanidin B2, 6. (—)-epicatechin...

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