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<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.

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