Red wine substituted esters involved in fruity aromatic expression: an enantiomeric approach to understand their sensory impact and their pathway formation

Abstract

Among red wines ethyl esters, those from short hydroxylated and branched-chain aliphatic acids constitute a family with a particular behavior and sensory importance. They have been previously discussed in the literature [1] and recent studies have established that some of them were strongly involved in of red wines’ fruity aroma [2]. As some among them have an asymmetrical carbon atom, it seemed important to separate their different enantiomers to obtain an accurate assessment of their organoleptic impact. Three chiral esters have been identified, presenting alkyl and/or hydroxyle substituants: ethyl 2-hydroxy-4-methylpentanoate, ethyl 2-methylbutanoate, and ethyl 3-hydroxybutanoate. They were present in wines with a single or both enantiomeric forms in various ratios, according to age. On the contrary of most of the ethyl esters, produced during alcoholic fermentation, these esters levels increased gradually over time and then stabilize after about four to five years. For those present under two enantiomeric forms, ratios were modified during ageing. For each ester of this type, the most powerful enantiomer, from an olfactive point of view, was found in relatively small amount at the end of alcoholic fermentation and was then particularly accumulated. The sensorial role of these chiral compounds has been established, revealing their role as natural enhancers of black-berry, red-berry and fresh-fruit aromas. Our data corroborate and specify those of Lytra et al. [2] and Pineau et al. [3] highlighting the impact of substituted esters in fruity expression of red wines. Considering their dynamic evolution of their concentration, these compounds seem to be produced on one hand during alcoholic fermentation by Saccharomyces cerevisiae from amino acids and on the other hand during aging by a chemical esterification from the corresponding substituted acids as previously suggested by Diaz-Maroto et al. [4]. In order to determine the precursors of these esters and to consider synthesis pathways, we have developed a method aimed at quantifying their corresponding substituted acids (2-hydroxy-4-methylpentanoic acid, 2-methylbutanoic acid, and 3-hydroxybutanoic acid) including, if applicable, the enantiomeric forms. Thanks to the quantification of these compounds, the chemical formation of substituted esters during aging as well as the mechanisms of formation of these compounds during alcoholic and malolactic fermentation was described.

References: 1. Guth, H. (1997) J. Agric. Food Chem.45:3027-3032. 2. Lytra, G., Tempere, S., Le Floch, A., de Revel, G., and Barbe, J.-C. (2013) J. Agric. Food Chem. 61:8504-8513. 3. Pineau, B., Barbe, J.-C., Van Leeuwen, C., Dubourdieu, D. (2009) J. Agric. Food Chem. 57:3702-3708. 4. Diaz-Maroto, M.C., Schneider, R., Baumes, R. (2005) J. Agric. Food Chem. 53: 3503-3509.