Analysis of Proanthocyanidin Cleavage Products Following Acid-Catalysis in the Presence of Excess Phloroglucinol

The analysis of proanthocyanidin cleavage products after acid-catalysis in the presence of excess phloroglucinol was investigated. In the developed analytical method, a solution of 0.1 N HCl in methanol, containing 50 g/L phloroglucinol and 10 g/L ascorbic acid was prepared. The proanthocyanidin of interest was reacted in this solution (5 g/L) at 50 °C for 20 min, and afterward combined with 5 volumes of 40 mM aqueous sodium acetate before analysis by reversed-phase HPLC using an aqueous acetic acid and methanol gradient. This procedure was used to investigate the composition of proanthocyanidins isolated from the seed and skin tissue of Vitis vinifera L. berries. The results compared favorably to results obtained when benzyl mercaptan was used as the trapping nucleophile, indicating that phloroglucinol is an effective reagent for this analysis. Keywords: Proanthocyanidin; tannin; flavan-3-ol; molar absorptivity; Vitis vinifera; grape; phloroglucinol; benzyl mercaptan; thiolysis; yield