OPTIMIZING THE IDENTIFICATION OF NEW THIOLS AT TRACE LEVEL IN AGED RED WINES USING NEW OAK WOOD FUNCTIONALISATION STRATEGY

Abstract

During bottle aging, many thiol compounds are involved in the expression of bouquet of great aged red wines according to the quality of the closure.1,2 Identifying thiol compounds in red wines is a challenging task due several drawbacks including, the complexity of the matrix, the low concentration of these impact compounds and the amount of wine needed.3,4

This work aims to develop a new strategy based on the functionalisation of oak wood organic extracts with H₂S, to produce new thiols, in order to mimic what can happen in red wine during bottle aging. Following this approach and through sensory analysis experiments, we demonstrated that the vanilla-like aroma of fresh oak wood was transformed into intense “meaty” nuances similar to those found in old but non oxidized red wines.5 Functionalized samples were analysed by gas chromatography coupled with a pulsed flame photometric detector (GC-PFPD) and olfactometry (GC-O) to optimize the reaction conditions. Analysis of functionalized oak wood organic extracts by GC-O and GC-PFPD led us to detect six OZ reminiscent of “meaty” nuances and associated with sulphur compounds. One of them was characterized by preparative multi-dimensional gas chromatography coupled with olfactometry and time of flight mass spectrometry (Prep-MDGC-O-TOF MS) and identified as 2-methoxybenzenethiol.

This thiol was also identified in red wines following extraction by SPE, separation and detection by means of GC-MS/MS (SRM mode). The validation of the quantification method was carried out before its use to study its distribution in wines, young and old from different appellations and according to the OTR (determined by coulometry) of the closure. We show that its concentration can reach the odour detection threshold determined at 607 ng/L. Following the same strategy, five other thiols reminiscent of “meaty” nuances, including 2,5-dimethylfuran-3-thiol, 5-methyl-2-furfurylthiol, o-toluenethiol, 2,6-dimethylbenzenethiol and 2,6-dimethoxybenzenethiol were also identified for the first time in red wines. Their sensory impact will also be discussed.