Proanthocyanidins in the Apple

SUMMARY A study was conducted on the acetone‐ and ethyl‐acetate‐extractable flavan polyphenols of Waldhöfler apples, an astringent‐tasting juice variety. The extracts were examined by cellulose thin‐layer chromatography with 5% n‐butanol and n‐butanol—acetic acid—water (BAW) as the developing solvents. (—) Epicatechin was the major monomeric flavan found; (+) catechin was present in smaller amounts. A large number of unknown flavans were also detected; most of these are thought to be dimerie or oligomeric in composition, since their RI values did not correspond to those of any known flavans. The predominating unknown substance, R 1 0.58 in 5% n‐butanol and 0.46 in BAW, was purified from ethyl acetate extracts by polyamide chromatography followed by solvent fractionation. The pure compound had a marked astringent taste. The IR and UV spectra were typical of flavans. On hydrolysis, cyanidin and epicatechin were produced. Methylation with diazomethane yielded a compound with the empirical formula C 3s H 42 O 12 H 2 O with a methoxyl content of 33.7%. NMR spectra indicated that condensations involved the A ring. Hydrolysis of the methylated derivative yielded tetramethyl epicatechin and a substance corresponding to tetramethyl flavan‐3,4‐diol and other unidentified intermediate products. It is thought that the purified proanthocyanidin is a dimer, or possibly an oligomer, containing (‐) epicatechin and 5,7,3′,4′‐flavan‐3,4‐diol as constituents. The other unknown flavans, not isolated in pure form, yielded cyanidin, (—) epicatechin, and a small amount of pelargonidin on hydrolysis.