Evolution of oak barrels C-glucosidic ellagitannins in model wine solution

Abstract

Oak wood has a significant impact on the chemical composition of wine, leading to transformations that influence its organoleptic properties, such as its aroma, structure, astringency, bitterness and color. Among the main extractible non-volatile polyphenol compounds released from oak wood, the ellagitannins are found [1]. The primary ellagitannins are C-glucosidic ellagitannins, like vescalagin and castalagin. Other compounds, including lyxose/xylose derivatives (grandinin, roburin E) and dimeric forms (roburins A, B, C, and D), are also present [2,3]. The ellagitannins possess multiple hydroxyl groups in ortho-positions, facilitating oxidation and condensation reactions with other wine compounds. The hydroalcoholic nature of wine make possible the extraction of these compounds from oak into the wine, but their high reactivity results in lower concentrations than expected in the final wine. In order to observe the compounds transferred from oak to wine, a model wine solution was used, ensuring the absence of microbial activity and preventing contamination from fermenting compounds. A model wine solution was put in two 225 L oak barrels for a period of twelve months to minimize the influence of naturally occurring wine components and microbial interference. The objectives of this study were i) to evaluate the evolution of ellagitannin levels in oak barrels after 12 months of aging, and ii) to analyze their derivative forms using liquid chromatography-mass spectrometry (LC/MS) and nuclear magnetic resonance (1D/2D-NMR). Results showed significant changes in the composition of ellagitannins over time, revealing the formation of new oxidation products and condensation products. The concentration of the eight main C-glucosidic ellagitannins extracted after twelve months of contact with oak wood tend to increase. Ellagitannins monomers (vescalagin, castalagin, grandinin and roburin E) increased drastically in concentration up to 8 months, from 1,93 mg/L to 23,84 mg/L in the case of vescalagin. The dimer concentrations, on the other hand, rise progressively, stabilizing from the 7th month. The derived compounds were observed in oxidative forms, hydrolyzed forms, or as ethanol adducts. Most of these compounds appear within the first months of analysis, initially at low concentrations that progressively increase over time. Nevertheless, the concentrations of certain compounds, for example, the oxidation form resulting from the oxidative solvolysis of vescalagin and β-1-O-ethylvescalagin, remain consistently low even after 8 months of aging. These findings contribute to a deeper understanding of the chemical dynamics between oak and wine, offering insights into the aging process and its impact on the final wine quality.

References

[1] Gadrat, M., Lavergne, J., Emo, C., Teissedre, P.-L., Chira, K. Validation of a mass spectrometry method to identify and quantify ellagitannins in oak wood and cognac during aging in oak barrels (2021) Food Chemistry.

[2] Chira, K., Anguellu, L., Da Costa, G., Richard, T., Pedrot, E., Jourdes, M., Teissedre, P.-L. New C-glycosidic ellagitannins formed upon oak wood toasting; identification and sensory evaluation (2020) Foods.

[3] Gadrat, M., Capello, Y., Emo, C., Lavergne, J., Quideau, S., Jourdes, M., Teissèdre, P.-L., Chira, K. Identification, quantitation and sensory contribution of new C-glucosidic ellagitannin-derived spirit compounds (2022) Food Chemistry.