Presence of Several Phenolic Components in Fruit Proanthocyanidins

Abstract

Forsyth and Roberts¹ reported that chromatographically homogeneous cacao proanthocyanidin dimer yielded epicathechin and a new leucocyanidin when heated with 0.1 N hydrochloric acid, and cyanidin when heated with stronger acid. Similar dimeric proanthocyanidins were isolated from Crataegus oxyacantha and Gleditschia triacanthos by Freudenberg and Weinges^2–5. The astringent proanthocyanidins isolated from various fruit tissues, unlike the above dimers, were found to be highly polymerized and not chromatographically mobile. This was true of the originally isolated persimmon proanthocyanidin^6,7 and of the more recently isolated persimmon⁸ and apple⁹ preparations. These purified preparations, which were not mobile on paper in any of the solvent systems tested, were, however, found to yield mobile phenolics without any accompanying anthocyanidins when heated with dilute hydrochloric acid. Under these conditions several chromatographically identified phenolics and a non-mobile but apparently less highly polymerized fraction were obtained. The original preparation, and the residue after dilute acid hydrolysis, which was insoluble in ethyl acetate, were found to yield identifiable anthocyanidins on heating with more concentrated hydrochloric acid. The results of these observations, which continued investigations previously reported on the mechanism of acid conversion of proanthocyanidins into their corresponding anthocyanidins¹⁰, are reported here.