Structure of Procyanidin Oligomers Isolated From Grape Seeds in Relation to Some of their Chemical Properties

Abstract

A micro-method using thiolysis followed by HPLC monitoring of the degradation products was developed to determine the structure of procyanidin oligomers available in small quantities (≤ 0.1 mg). It was successfully applied to a series of procyanidins isolated from grape seeds, allowing the identification of procyanidins dimers B5 to B8 linked by C4 {\textrightarrow} C6 bonds, six procyanidin trimers with C4 {\textrightarrow} C8 and C4 {\textrightarrow} C6 linkages, and six galloylated dimers and trimers, along with the four C4 {\textrightarrow} C8 linked dimers, Bl to B4. The influence of procyanidin structural variations on their interactions with proteins, free radical scavenging effect, and oxidation was studied using these compounds. Protein-procyanidin interactions increased with the degree of polymerization, the number of galloyl substituents, and the extent of C4{\textrightarrow} C6 linkages. Galloylation increased scavenger capacity of procyanidin dimers for Superoxide anion (O2-{\textbullet}) and hydroxyl (su{\textbullet}OH) radicals. The type of C {\textrightarrow} C linkage and the esterification position were also important. None of the molecules tested was oxidizable by grape polyphenoloxidase, but they were all oxi-dized by the enzymically generated caffeoyl tartaric acid o-quinones. In addition, galloylated procyanidins seemed to undergo condensation reactions faster than the corresponding non-galloylated ones, even though their rate of oxidation was similar.