This aim of this work was to identify the odorant compounds responsible for the typical sensory descriptors attributed to freshly distilled Cognac spirits, not matured in barrels. Panelists were first selected and trained for gas chromatography-olfactometry. Among the 150 volatile compounds identified by gas chromatography-mass spectrometry analysis, only 34 are mainly responsible for the odors detected in the spirits. The "butter" descriptor is explained by the presence of diacetyl, the "hay" descriptor by nerolidol, the "grass" descriptor mainly by Z-3-hexen-1-ol, but also by other compounds, the "pear" and "banana" descriptors by 2- and 3-methylbutyl acetates, the "rose" descriptor by 2-phenylethyl acetate, and the "lime tree" descriptor by linalool. This study demonstrated that many odorant molecules are already present in freshly distilled Cognac, thereby giving the spirit its specific aroma.

Cognac wine spirit has a complex composition in volatile compounds which contributes to its organoleptic profile. This work focused on the batch distillation process and, in particular, on volatile compounds specifically produced by chemical reactions during the distillation of Cognac wine spirit, traditionally conducted in two steps with charentais pot stills. The aim of this study was to characterize these volatile compounds formed during distillation. Sampling has been performed on the distillates and inside the boiler during a typical Cognac distillation. The analysis of these samples allowed us to perform a mass balance and to point out several types of volatile compounds whose quantities strongly increased during the distillation process. These compounds were distinguished by their chemical family. It has been found that the first distillation step was decisive for the formation of volatile compounds. Moreover, 2 esters, 3 aldehydes, 12 norisoprenoids, and 3 terpenes were shown to be generated during the process. These results suggest that some volatile compounds found in Cognac spirit are formed during distillation due to chemical reactions induced by high temperature. These findings give important indications to professional distillers in order to enhance the product's quality.

BackgroundThe acid component of grape berries, originating in the metabolism of malate and tartrate, the latter being less well-known than the former, is a key factor at play in the microbiological stability of wines destined for distillation. Grape acidity is increasingly affected by climate changes. The ability to compare two vintages with contrasted climatic conditions may contribute to a global understanding of the regulation of acid metabolism and the future consequences for berry composition.ResultsThe results of the analyses (molecular, protein, enzymatic) of tartrate biosynthesis pathways were compared with the developmental accumulation of tartrate in Ugni blanc grape berries, from floral bud to maturity. The existence of two distinct steps during this pathway was confirmed: one prior to ascorbate, with phases of VvGME, VvVTC2, VvVTC4, VvL-GalDH, VvGLDH gene expression and abundant protein, different for each vintage; the other downstream of ascorbate, leading to the synthesis of tartrate with maximum VvL-IdnDH genetic and protein expression towards the beginning of the growth process, and in correlation with enzyme activity regardless of the vintage.ConclusionsOverall results suggest that the two steps of this pathway do not appear to be regulated in the same way and could both be activated very early on during berry development.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-016-0833-1) contains supplementary material, which is available to authorized users.

No abstract

Eutypa lata is the causal agent of eutypa dieback, one of the most destructive grapevine trunk disease that causes severe economic losses in vineyards worldwide. This fungus causes brown sectorial necrosis in wood which affect the vegetative growth. Despite intense research efforts made in the past years, no cure currently exists for this disease. Host responses to eutypa dieback are difficult to address because E. lata is a wood pathogen that causes foliar symptoms several years after infection. With the aim to classify the level of susceptibility of grapevine cultivars to the foliar symptoms caused by E. lata , artificial inoculations of Merlot, Cabernet Sauvignon, and Ugni Blanc were conducted over 3 years. Merlot was the most tolerant cultivar, whereas Ugni Blanc and Cabernet Sauvignon exhibited higher and differential levels of susceptibility. We took advantage of their contrasting phenotypes to explore their defense responses, including the activation of pathogenesis-related ( PR ) genes, oxylipin and phenylpropanoid pathways and the accumulation of stilbenes. These analyses were carried out using the millicell system that enables the molecular dialogue between E. lata mycelium and grapevine leaves to take place without physical contact. Merlot responded to E. lata by inducing the expression of a large number of defense-related genes. On the contrary, Ugni Blanc failed to activate such defense responses despite being able to perceive the fungus. To gain insight into the role of carbon partitioning in E. lata infected grapevine, we monitored the expression of plant genes involved in sugar transport and cleavage, and measured invertase activities. Our results evidence a coordinated up-regulation of VvHT5 and VvcwINV genes, and a stimulation of the cell wall invertase activity in leaves of Merlot elicited by E. lata , but not in Ugni Blanc. Altogether, this study indicates that the degree of cultivar susceptibility is associated with the activation of host defense responses, including extracellular sucrolytic machinery and hexose uptake during the grapevine/ E. lata interaction. Given the role of these activities in governing carbon allocation through the plant, we postulate that the availability of sugar resources for either the host or the fungus is crucial for the outcome of the interaction.