Identification, distribution, and sensory contribution of (R/S)-abhexone enantiomers to the aroma of old red wines

Abstract

The evolution of the aroma of red wines during bottle ageing is a complex phenomenon resulting from chemical changes that can, give rise to the characteristic ageing bouquet reminiscent of mint, truffle, empyreumatic or spicy notes. To the best of our knowledge, this evolution depends on intrinsic wine composition and on extrinsic storage factors, particularly the type and quality of the closure. The objective of this study was to identify markers of wine evolution in relation to bottle ageing. After 15 years of bottle storage, we analysed two samples of the same wine sealed with different stoppers that offered different sensory balances: from spicy and empyreumatic notes (low OTR 0.3 mg/year) to intense prune aromas (high OTR 4.5 mg/year). These samples were first analysed by gas chromatography coupled with olfactometry (GC-O) where an intense odorant zone (OZ) reminiscent of spicy and curry aroma was detected in low OTR wine (IRLpolar 2235, IRLnon-polar 1185) and characterized by using different analytical technics, including semi preparative HPLC fractionation combined with GC-O-MS analysis. Our analytical strategy led to identify (R/S)-5-ethyl-3-hydroxy-4-methylfuran-2(5H)-one in red wines also called (R/S)-abhexone. This chiral furanone can be found at high level in white wines, thanks to an aldol reaction involving propanal and α-ketobutyric acid. We validated a GC-MS/MS quantification method to study its distribution in different Merlot/Cabernet Sauvignon blend (n = 67). Concentrations are higher in older red wines, reaching several µg/L above the perception threshold (0.60 µg/L). Surprisingly, highest levels were not detected in oxidized red wines. Sensory analysis of increasing amounts of (R/S)-abhexone were carried out, demonstrating that it reduces the fruitiness of red wines while increasing the “spicy note” intensity. Pure abhexone enantiomers (R or S) were separated by semi preparative HPLC (chiral phase) whereas absolute configuration was determined by vibrational circular dichroism. Enantiomer distribution was evaluated by GC-MS/MS (polar pre-column and a chiral column). Analysis of red wines (n = 30) showed that (S)-abhexone was predominant (60–90 %) and the most odorous form (ten times more intense). These results improved our understanding of abhexone, an odorant marker that contributes to the sensory balance and complexity of old red wines.

References

Collin, S., Nizet, S., Claeys Bouuaert, T., & Despatures, P.-M. (2012). Main Odorants in Jura Flor-Sherry Wines. Relative Contributions of Sotolon, Abhexon, and Theaspirane-Derived Compounds. Journal of Agricultural and Food Chemistry, 60(1), 380–387.