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

A soluble proanthocyanidin polymer (PAP; condensed tannin) has been hi stologically localized in the pallisade layer of the alfalfa seedcoat, purified, and characterized by spectroscopic, chemical, and biochemic al procedures. The polymer consists principally (91-93%) of 4 --> 8 li nked (-)-epicatechin units with a mean degree of polymerization of 5. (+)-Catechin is the predominant terminal unit. Only traces of prodelph inidin units were detected. No significant quantities of low molecular weight flavan-3-ols could be detected in ethyl acetate fractions of s eed 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 rat es similar to that of monomeric flavonoids. Comparison of binding of P APs from alfalfa seed and sainfoin leaf with bovine serum albumin at p H 2.5 and 6 indicated no significant differences between the tannins; however, there was a significant pH effect at higher tannin concentrat ions with protein binding greater at pH 6.0 than at pH 2.5.