PURIFICATION AND CHARACTERIZATION OF A PROANTHOCYANIDIN POLYMER FROM SEED OF ALFALFA (MEDICAGO-SATIVA CV BEAVER)

A soluble proanthocyanidin polymer (PAP; condensed tannin) has been histologically localized in the pallisade layer of the alfalfa seedcoat, purified, and characterized by spectroscopic, chemical, and biochemical procedures. The polymer consists principally (91-93%) of 4 --> 8 linked (-)-epicatechin units with a mean degree of polymerization of 5. (+)-Catechin is the predominant terminal unit. Only traces of prodelphinidin units were detected. No significant quantities of low molecular weight flavan-3-ols could be detected in ethyl acetate fractions of seed extracts, but analysis of seed leachate indicated the presence of (+)-catechin, (-)-epicatechin, and higher molecular weight oligomeric flavanols. Time course studies indicated that PAPs were leached at rates similar to that of monomeric flavonoids. Comparison of binding of PAPs from alfalfa seed and sainfoin leaf with bovine serum albumin at pH 2.5 and 6 indicated no significant differences between the tannins; however, there was a significant pH effect at higher tannin concentrations with protein binding greater at pH 6.0 than at pH 2.5.