Wine tannins: What place for grape seed?

Grapevine downy mildew is a disease of foliage caused by Oomycete Plasmopara viticola an endoparasite that develops inside grapevine organs and can infect virtually every green organ. Downy mildew is one of the most destructive diseases in wine-growing regions, drastically reducing yield and fruit quality. Traditional manual disease detection relies on farm experts. Human field scouting has been widely used for monitoring the disease progress, however, is costly, laborious, subjective, and often imprecise.

Among red wines ethyl esters, those from short hydroxylated and branched-chain aliphatic acids constitute a family with a particular behavior and sensory importance. They have been previously discussed in the literature [1] and recent studies have established that some of them were strongly involved in of red wines’ fruity aroma [2]. As some among them have an asymmetrical carbon atom, it seemed important to separate their different enantiomers to obtain an accurate assessment of their organoleptic impact. Three chiral esters have been identified, presenting alkyl and/or hydroxyle substituants: ethyl 2-hydroxy-4-methylpentanoate, ethyl 2-methylbutanoate, and ethyl 3-hydroxybutanoate.

Grape phenolic content is an important quality factor that influences the appearance and mouthfeel of premium red wines.

Commercial oenological tannins (TECs) are widely used in the wine industry. TECs are rich in condensed tannins, hydrolyzable tannins or a mixture of both. Wine grapes are a important source of proanthocyanidins or condensed tannins while oak wood possess a high concentration of hydrolyzable tannins (Obreque-Slier et al., 2009). TECs contribute with the antioxidant capacity of wine, catalyze oxide-reduction reactions and participate in the removal of sulfur compounds and metals.

Tempranillo Tinto (TT) is the third-most planted red wine variety in the world, and it is mostly grown in the Iberian Peninsula. Spontaneous somatic variation appearing during vegetative propagation can be exploited to improve elite varieties as Tempranillo Tinto, including the selection of new phenotypes enhancing berry quality. We described previously that a somatic variant of TT with darker fruit color, the clone VN21, exhibits increased extractability of polyphenols during the winemaking process. To unravel the molecular mechanism underlying this phenomenon, we performed whole-genome resequencing to compare VN21 to other TT clones, revealing a 10 Mb deletion in chromosome 11 that likely affected only the L1 meristem cell layer of VN21 and tissues derived from it, such as external cell layers of berry skin.