Study of the polyphenolic composition of grapes and red wines of different vitis vinifera varieties cultivated in Uruguay

Doctoral thesis abstract

Abstract

The sustainability of vitiviniculture in Uruguay depends on the quality and typicity of its wines. The wines of Tannat stand out, variety of good local adaptation with outstanding oenological characteristics and of scarce international distribution, as well as the particular expression of other cultivars in our environment. Proper management of this potential requires knowledge that assists management decisions in the field and the winery. Distinctive characteristics of red wine as color, astringency and contents in bioactive compounds are due to the presence of polyphenols, compounds derived from the secondary metabolism of the vine. The objective of the research was to study the effect of the cultivar and the maturity of the grape, on the tannins of the berry, its relative distribution in skins and seeds, and its extraction in the wine. Also, to deepen in the study of the stilbenes, flavonols and pigments of grapes produced in the south of Uruguay, and in the respective red wines elaborated on an experimental scale. We worked with Tannat, Syrah and Marselan cultivars during two harvests, considering grapes of different degrees of commercial maturity. The phenolic composition of the berries, as well as that of the wines and pomaces, was characterized by HPLC-MSn. The proportion of tannins in skins and seeds in the wine depended mainly on the cultivar. The Marselan wines presented very high proportions of seed tannins while the Syrah and Tannat, of skins. Pigment extraction was selective, particularly low for p-cumarylated derivatives. The contents of stilbenes remained very stable in wine. The potential of polyphenolic synthesis of the vine in southern Uruguay was evident in the three cultivars, having identified in them for the first time flavonols acylated with acetic acid and p-coumaric. In Tannat a pigment acylated with ferulic acid was characteristic of its profile. A contribution to the characterization of grapes and wines grown in the country ware made, and are expected to assist field and winery decisions as well as to encourage future research.