Flavor composition has been defined as a complex attribute of fruit quality, in which the mix of sugars, acids and volatiles play a primary role. In table grapes (Vitis vinifera L.), sweetness and sourness are the most important flavor attributes for fresh consumption. However, most of the studies available have been performed on wine grapes, which are grown, cultured and processed differently to table grapes. Therefore, the objective of this work was to characterize the changes in sugars and organic acids during the development of 'Thompson Seedless', 'Red Globe' and 'Crimson Seedless' grown under the same agroclimatic conditions. Each variety was sampled weekly from 2 wk before véraison until commercial harvest. Sugars and organic acids were quantified by high performance liquid chromatography (HPLC) equipped with an evaporative light scattering detector (ELSD) and ultra violet detector, respectively. The ranges of acid and sugars concentrations found in grapes were as follows: tartaric acid, 1. . Among sugars, glucose was the most abundant one in early stages and then it decreased until the harvest period, when the amount of fructose and glucose converged to an average of 47% for each sugar. Despite organic acids reaching steady levels 3-4 wk before commercial harvest, there were important differences in the organic acid profiles among varieties, with 'Thompson Seedless' showing the lowest tartaric/malic acid ratio of 1.19. These differences are an important aspect in terms of overall flavor.

International audienceAs a consequence of the non-climacteric status of grapes (Vitis vinifera), ethylene biosynthesis and signal transduction have scarcely been studied in this fruit. In spite this drawback, the available information suggests a role for ethylene in ripening grape berries. In this work, we report the identification of three homologous genes that encode 1-aminocyclopropane-1-carboxylic acid oxidase (ACO), a key component of ethylene biosynthesis. A comparison of protein sequences revealed that all three VvACOs harbor a 2OG-Fe(II) oxygenase domain, which is typical of the ACO gene family; however, VvACO1 showed a higher amino acid sequence homology with VvACO2 than with VvACO3. The expression pattern of VvACOs and the effect of exogenous ethylene on their transcript accumulation were evaluated during table grape berry development in the "Thompson Seedless" cultivar. A peak in VvACO1 transcript accumulation levels was registered around veraison that was 4-fold higher than at harvest, and this peak was confirmed during a second season in grapes that were harvested from three different vineyards. An enhancement in ethylene production and VvACO genes transcript levels was observed in grapes sprayed with ethephon during berry development. However, VvACO1 transcripts reached the highest accumulation earlier than VvACO2 and VvACO3. Altogether, these data confirmed that ethylene may have a role in some aspects of the grape ripening process, and they also highlighted the potential use of some VvACO genes as molecular markers for identifying grape veraison stages in grapes

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