Abstract
Flavan-3-ols consist of flavan-3-ol monomers and polymers with different degrees of polymerization (DP). In this study, flavan-3-ol extracts from grape seeds were well separated into three fractions including monomers, oligomers (2 < DP < 10) and polymers (DP > 10), by means of normal-phase HPLC-MS. The different patterns of these three fractions were analyzed in three Vitis vinifera cultivars (‘Shiraz’, ‘Cabernet Sauvignon’ and ‘Marselan’) seeds from veraison to harvest. The results showed: (1) polymers were the main form of flavan-3-ols in grape seeds and monomers accounted for only a small proportion; (2) the contents of flavan-3-ol monomers in the seeds of three grape cultivars all exhibited a gradually decreasing trend with a little fluctuation, whereas the patterns of the change of contents of oligomers and polymers were extremely different among grape cultivars; the contents of flavan-3-ol oligomers were enhanced in the seeds of ‘Cabernet Sauvignon’, but were reduced in the other two cultivars; (3) with regard to the proportion of flavan-3-ols with a certain DP to total flavan-3-ols, both flavan-3-ol monomers and flavan-3-ols with low DP fell in proportion, while the flavan-3-ols with high DP increased correspondingly. These findings indicate that flavan-3-ol polymerization in developing seeds is variety-dependent and may be genetically regulated.
Highlights
Flavan-3-ols are widely distributed in higher plants like grape
Flavan-3-ol monomers to decamers were well separated and the polymers larger than decamers were eluted as a single peak corresponding to a retention time of 50 min (Figure 1)
Individual monomeric flavan-3-ols could be exactly measured in quantity, while the oligomeric and polymeric falvan-3-ols could be relatively quantified by using the standard procyanidin B1 as reference
Summary
Flavan-3-ols are widely distributed in higher plants like grape. Abundant flavan-3-ols are present in grape skins and seeds [1,2,3], and are transferred into wine during must fermentation [4,5], providing wine with organoleptic properties such as astringency, bitterness, and colour stability [6,7]. Similar trends of flavan-3-ols during berry development have been reported, that is, the generation of flavan-3-ols in grape berries commences with the flowering stage and flavan-3-ols accumulate rapidly towards a maximum around veraison, followed by a decrease at subsequent ripening stage In these studies, flavan-3-ols with low DP (DP ≤ 4) were mainly measured using reverse-phase HPLC, and polymeric flavan-3-ols were analyzed mostly through acid-catalyzed cleavage in the presence of excess phloroglucinol or benzyl mercaptan [22,23,24]. We fractioned flavan-3-ol extracts from grape seeds into three fractions according to their DP by normal phase HPLC-MS, and quantified each fraction On this basis, the changes of flavan-3-ols with different DP were investigated in ripening seeds of three winegrape cultivars (‘Shiraz’, ‘Cabernet Sauvignon’ and ‘Marselan’) after veraison. This work will provide some valuable information for uncovering mechanism of flavan-3-ol polymerization
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