Jorge Manuel Ricardo da Silva

Procyanidin dimers and trimers from grape seeds

Abstract Fractionation of a grape (Vitis vinifera) seed extract yielded various natural procyanidin dimers and trimers isolated and identified for the first time in grapes: procyanidin dimers B5 [epicatechin-(4β → 6)-epicatechin], B6 [catechin-(4α → 6)-catechin] and B8 [catechin-(4α → 6)-epicatechin]; four procyanidin trimers [epicatechin-(4β → 6)-epicatechin-(4β → 8)-epicatechin], [epicatechin-(4β → 8)-epicatechin-(4β → 6)-catechin], [epicatechin-(4β → 8)-epicatechin-(4β → 6)-epicatechin], [epicatechin-(4β → 6)-epicatechin-(4β → 8)-catechin] along with five galloyl procyanidins: B2 3-O-gallate, B1 3-O-gallate, B4 3′-O-gallate, B2 3,3′-di-O-gallate and [epicatechin-(4β → 8)-epicatechin 3-O-gallate-(4β → 8)-catechin]. The presence of (+)-catechin, (−)-epicatechin, (−)-epicatechin 3-O-gallate, procyanidins dimers B1, B2, B3, B4, B7, B2 3′-O-gallate and procyanidin trimers C1 and [epicatechin-(4β → 8)-epicatechin-(4β → 8)-catechin] was also confirmed. The structures of all these compounds were elucidated by enzymatic hydrolysis, complete acid hydrolysis, partial acid-catalysed degradation with phloroglucinol and phenylmethanethiol, FABMS and 1H NMR. Separation of procyanidins and of their phloroglucinol or phenylmethanethiol adducts was achieved by TLC on silica plates and HPLC.

Comparative study of the phenolic composition of seeds and skins from Carménère and Cabernet Sauvignon grape varieties (Vitis vinifera L.) during ripening.

The phenolic composition of skins and seeds from Vitis vinifera L. cv. Carménère and Cabernet Sauvignon grapes during ripening was evaluated by high-performance liquid chromatography-diode array detection and spectrophotometric analysis. As compared to Cabernet Sauvignon grape skins, Carménère grape skins presented higher contents of total anthocyanins, monomeric flavan-3-ols, and total flavonoids, a higher mean degree of polymerization, a higher percentage of galloylation, a higher average molecular weight of the flavanol fraction, and a higher color intensity. As compared to Cabernet Sauvignon grape seeds, Carménère grape seeds presented a lower content of monomeric flavan-3-ols, a higher mean degree of polymerization, a higher percentage of galloylation, a higher average molecular weight of the flavanol fraction, a lower content of (+)-catechin, and higher contents of (-)-epicatechin, epicatechin-3-O-gallate, gallic acid, and dimeric procyanidins esterified with gallic acid. Altogether, we conclude that Carménère grapes present a differential composition and evolution of phenolic compounds when compared to Cabernet Sauvignon grapes.

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

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 → C6 bonds, six procyanidin trimers with C4 → C8 and C4 → C6 linkages, and six galloylated dimers and trimers, along with the four C4 → 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→ C6 linkages. Galloylation increased scavenger capacity of procyanidin dimers for Superoxide anion (O2 -•) and hydroxyl (su•OH) radicals. The type of C → 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.