Procyanidin dimers and trimer C1 were synthesized, whereas (-)-epicatechin
O-gallate and B2-3"-O-gallate were isolated from grape seeds. Human saliva
was separated into two fractions. One of these was mainly a-amylase and the
other mainly proline-rich proteins (PRPs). The procyanidin compounds were
combined with each of the saliva protein fractions and with bovine serum al
bumin. The protein-polyphenol interactions were observed using nephelometry
. (+)-Catechin had a higher tannin specific activity (TSA) for PRPs than (-
)-epicatechin (1.45 versus 0.65 nephelos turbidity units/mg of polyphenol).
This indicated the effect of the stereochemistry of flavan-3-ols on their
interaction with proteins. Procyanidin dimers linked through a C(4)-C(8) in
terflavanoid bond had consistently greater TSA than their counterparts with
a C(4)-C(6) linkage. Esterification of a galloyl group to the C(3) hydroxy
l function of(-)-epicatechin or to the epicatechin moiety of procyanidin di
mer B2 increased TSA. This was not as strong an effect for the dimer, proba
bly as a result of the expected "closed" structure of B2-3"-O-gallate.