Structural Features of Procyanidin Interactions with Salivary Proteins

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Abstract
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 α-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 albumin. 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) interflavanoid bond had consistently greater TSA than their counterparts with a C(4)−C(6) linkage. Esterification of a galloyl group to the C(3) hydroxyl function of (−)-epicatechin or to the epicatechin moiety of procyanidin dimer B2 increased TSA. This was not as strong an effect for the dimer, probably as a result of the expected “closed” structure of B2−3‘ ‘-O-gallate. Keywords: Astringency; nephelometry; grape seeds; procyanidin; salivary proteins; BSA