Characterization of monomeric and oligomeric flavan-3-ols from unripe almond fruits

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The flavan-3-ol composition of unripe sweet almond fruits (Prunus amygdalus) was analysed. Isolation of compounds was performed on a methanol extract of the fruit by gel chromatography on Sephadex LH-20 and then by preparative high pressure liquid chromatography. Identification of compounds was carried out by different kinds of hydrolyses. Two monomers, (+)-catechin and (−)-epicatechin, and 15 oligomeric procyanidins, (six dimers, seven trimers and two tetramers) were identified. Higher procyanidins present in the extract were estimated to have an average degree of polymerization of five by using a method based on hydrolysis in the presence of phloroglucinol. A tentative analysis was also carried out by liquid chromatography-mass spectrometry (LC-MS) in order to explore the potential of this recently introduced technique for the analysis of proanthocyanidins. The results obtained permitted the confirmation of the identifications made by hydrolysis techniques and also the detection and pre-identification of other minor compounds as two possible A-type procyanidins. The possibility of resolving peaks of co-eluting compounds was shown as another interesting aspect offered by the LC-MS technique.