Transfer of tannin characteristics from grape skins or seeds to wine-like solutions and their impact on potential astringency

Abstract

A simulated maceration was carried out with skins or seeds of Aglianico, Merlot and Cabernet Sauvignon grape cultivars in order to study the entity of the transfer of tannins from grape to wine. The structural characteristics of skins and seeds extracts (native tannins) and corresponding wine-like solutions (macerated tannins) were analysed by phloroglucinolysis. Their potential astringency was evaluated according to the reactivity towards salivary proteins by the Saliva Precipitation Index (SPI). From grape to wine-like solution, the transfer of structural characteristics varied differently for skins and seeds. A significant influence of extraction method and grape variety was also stated, principally as regard the percentage of prodelphinidins (%P) for skins, and of galloylation (%G) for seeds. For some parameters that were able to differentiate grapes through the maceration process, a cultivar effect emerged. Reactivity of tannins also differed, but not for seeds. For Aglianico native and macerated tannins, the highest in SPIs, seeds monomers and oligomers were quantified by HPLC/MS. Principal Component Analysis (PCA) allowed to reveal the structural characteristics mainly associated with the reactivity of tannins towards salivary proteins. The proanthocyanidins content and the %G increased potential astringency, while it was reduced by the %P.