Abstract
<p class="Sansinterligne1" style="text-align: justify;"><strong>Aim</strong>: Proanthocyanidin (PA) content, composition and evolution during berry development was determined in two cv., Nebbiolo and Barbera, quite different in their polyphenolic profile.</p><p class="Standard" style="text-align: justify;"><strong>Methods and results</strong>: PAs were extracted separately from seeds and skins, before véraison until maturity. Intact extracts were fractionated according to PA degree of polymerization. Nebbiolo grapes presented a significantly higher PA content in both seeds and skins. PA depolymerization reactions as well as a weaker decrease in polymeric PAs occurred in Barbera skins. Oligomeric PAs prevailed over polymeric ones in Barbera seeds. At harvest, Nebbiolo skins presented a significantly higher percentage of oligomeric PAs, while monomeric and oligomeric flavanol percentages were significantly higher in Barbera seeds.</p><p class="Standard" style="text-align: justify;"><strong>Conclusion</strong>: Barbera and Nebbiolo grapes differ also in their PA total amount and structure. PA content in grape skins and seeds, their distribution in monomeric, oligomeric and polymeric fractions, as well as their decrease rate during fruit ripening are different between the cv.</p><strong>Significance and impact</strong> <strong>of the study</strong>: The fractionation results, obtained for Nebbiolo and Barbera grapes for the first time, highlight how grape variety affects the PA profile. Furthermore, this study is the basis for better understanding the astringency and bitter sensation in Barbera and Nebbiolo grapes and wines.
Highlights
Grape tannins represent a significant organoleptic component of wines and are an important contributor to wine quality.The term tannin, in wine, describes proanthocyanidins (PAs) which are oligomers and polymers of flavan-3-ol units (Downey et al, 2003)
Barbera grape skins were significantly less rich in PAs and flavan-3-ols measured by the vanillin assay than Nebbiolo grape skins (Figure 1a)
PA and V measurements showed that PA content in skin was high prior to véraison, decreased during ripening, as previously reported for other cultivars (Downey et al, 2003) as well as for Nebbiolo and Barbera (Di Stefano et al, 2002)
Summary
The term tannin, in wine, describes proanthocyanidins (PAs) which are oligomers and polymers of flavan-3-ol units (Downey et al, 2003). PAs are present mainly in skins (Souquet et al, 1996) and seeds (Prieur et al, 1994) of grape berries. Their accumulation occurs early in berry development and is completed when ripening starts (Bogs et al, 2005). Flavan-3-ol monomers and PAs share the same biosynthetic pathway with anthocyanidins, which are red grape pigments, and with flavonols, which contribute to both bitter taste and color stability of red wine (Baranac et al, 1997).
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