Identification, quantification and organoleptic impact of « dried fruit » molecular markers in Merlot and Cabernet Sauvignon grapes and in red wines

Abstract

The aromas found in young Bordeaux red wines made with Merlot and Cabernet Sauvignon suggest a complex mixture of aromas of fresh red fruits such as cherry or blackberry for Merlot, and strawberry or blackcurrant for Cabernet Sauvignon. The aromas of these wines are closely linked with the maturity of the grapes. The climate change that has occurred during the last decade in Bordeaux has induced changes in the ripening conditions of grape berries. It is now widely admitted that over-ripening of the berries during hot and dry summers results in the development of characteristic flavors reminiscent of cooked fruits (fig, prune). The presence of these overriding odors found in both musts and young wines affects the quality and subtlety of the wine flavor and may shorten its shelf life. The main goal of this research was to identify key aroma compounds involved in “overripened” red wines with an intense prune, cooked fruit aroma. Gas chromatography coupled with olfactometry and mass spectrometry (GC-O-MS) was used in order to find odorant zones (OZ) and identify volatile compounds responsible for the cooked fruit aroma in Merlot and Cabernet Sauvignon (CS) grapes. As a result, several OZ of cooked fruits were highlighted and identified by GC-MS. The analysis of many musts and wines marked or not by dried fruit flavors showed that furaneol (caramel), γ-nonalactone (coconut, cooked peach) and (Z)-1,5-octadien-3-one (geranium) play a role in this aroma. Furaneol and γ-nonalactone are well-known compounds in wines. On the contrary, the influence of (Z)-1,5-octadien-3-one is reported for the first time in musts from healthy grapes. A first quantification method of this ketone using SPME-GC-CI-MS was also validated in terms of repeatability, linearity and limits of detection. Perception thresholds in model solution were determined: 0.0022 ng/L in model solution of must, 9 ng/L in Merlot must and 1.2 ng/L in wine model solution. This compound, which is reminiscent of geranium, is extremely intense. Its quantification was performed in musts marked or not by dried fruit flavors. Its concentration in musts marked by these flavors can reach 80 ng/L. The correlation between the concentration of these compounds including (Z)-1,5-octadien-3-one, furaneol and γ-nonalactone and their sensory analysis is described. The details of this study and the consequences of the level and distribution of these compounds in musts and wines on the determination of factors (harvest date, light, vine) associated with their formation are also presented.