Proanthocyanidin (PA) polymers (condensed tannins) were extracted from sainfoin leaves (Onobrychis viciifolia Scop.) at different stages of plant development. Analysis of the phloroglucinol degradation products by high-performance liquid chromatography showed that catechin, epicatechin, gallocatechin, and epigallocatechin were present as terminal units at all stages, while gallocatechin and epigallocatechin were the predominant extension units with lesser amounts of epicatechin incorporated at early stages. Catechin was not incorporated as an extension unit. The number-average molecular weight and degree of polymerization increased with leaf development. There was a very distinct change in the isomerization and degree of hydroxylation of the polymer constituents with development. The composition of ct'sisomers decreased from 83 to 48% and the proportion of trihydroxylated B-rings increased from 60 to 90% with increasing leaf maturity.

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