Characterization of Glycosidically Bound Aroma Compounds of País cv. grapes of different Chilean zones

The use of multivariate statistics to correlate chemical data to spectral information seems as a valid alternative for the quantification of red wine phenolics. The advantages of these techniques include simplicity and cost effectiveness together with the limited time of analysis required. Although many publications on this subject are nowadays available in the literature most of them only reported feasibility studies. In this study 400 samples from thirteen fermentations including five different cultivars plus 150 wine samples from a varying number of vintages were submitted to spectrophotometric and chromatographic phenolic analysis.

During red wine ageing or conservation, color and taste change and astringency tends to reduce. These changes result from reactions of flavan-3-ols and/or anthocyanins among which condensation reactions with acetaldehyde are particularly important. The full characterization of these reactions has not been fully achieved because of difficulties in extracting and separating the newly formed compounds directly from wine. Model solutions mimicking food products constitute a simplified medium for their exploration, allowing the detection of the newly formed compounds, their isolation, and their structure elucidation.

Ellagitannins (ETs) have been reported to be the main phenolic compounds found in oak wood. These compounds, belonging to the hydrolysable tannin class of polyphenols, are esters of hexahydroxydiphenic acid (HHDP) and a polyol, usually glucose or quinic acid. They own their name to their capacity to be hydrolysed and liberate ellagic acid and they have an impact on astringency and bitterness sensation, which is strongly dependant on their structure. The toasting phase is particularly crucial in barrels fabrication and influences wood composition.

Polysaccharides and more specifically pectins, make up a significant portion of the cell wall material of the plant cells including the grapes. During the fruit ripening the associated softening is related to the breakdown of the cell wall polysaccharides. During this process, it is expected that polysaccharides that are soluble in red wine will be formed influencing its texture. Anthocyanins are responsible for the wine color and tannins for the astringency, body and bitterness of the wine. In the skins, these compounds are located in the cell vacuoles and the barrier that conditions their extractability is the skin cell wall that may determine the mechanical resistance, the texture and the ease of processing berries. The aim of this work was study the evolution of the polysaccharides and the anthocyanin and tannin extractability during the ripening period in Cabernet Sauvignon grapes, trying to correlate these variables.

An alternative to improve grape quality is the application to the vineyard of elicitors. Although these compounds were first used to increase resistance of plants against pathogens, it has been found that they are also able to induce mechanisms involved in the synthesis of phenolic compounds and some amino acids. However, researches about the influence of elicitors on grape volatile composition are scarcely. Therefore, the aim of this work was to study the influence of methyl jasmonate (MeJ) foliar application on grape aroma composition over three consecutive vintages. MeJ was applied to Tempranillo grapevines at a concentration of 10 mM in 2013, 2014, and 2015 years. Control plants were sprayed with water.