Developing a green sensory approach to taste oak ellagitannins

Abstract

Oak barrels release a complex mixture of compounds into wine that shape organoleptic properties, such as its aroma, structure and colour. Among these compounds, ellagitannins are non-volatile hydrolysable tannins and are key contributors to astringency and bitterness1. However, their individual sensory properties remain difficult to assess. Ellagitannins are naturally abundant in oak wood, whereas their concentrations in wine remain relatively low due to partial extraction and chemical transformations during aging. In practice, these compounds are highly reactive and interact with wine components such as condensed tannins and anthocyanins, leading to an underestimation of their individual sensory contribution. The aim of this work was to develop a sensory-oriented approach to study C-glucosidic ellagitannins using extraction methods compatible with tasting. Several extraction strategies were tested, including aqueous and hydroalcoholic approaches, to obtain ellagitannin-rich fractions from oak wood using food-grade, environmentally friendly solvents. These “green” extracts were designed to preserve the integrity of the compounds while ensuring safety and acceptability for sensory evaluation. The extracts were analysed using liquid chromatography coupled with time-of-flight mass spectrometry (HPLC–TOF–MS). They contained the major C-glucosidic ellagitannins (castalagin, vescalagin, grandinin and roburins A, B, C, D and E) along with other naturally co-extracted compounds, providing a simplified yet realistic representation of oak composition. By comparing extracts obtained with different extraction conditions, it was possible to highlight differences in ellagitannin concentration and identify the most ellagitannin-rich fractions. The extraction yields indicated that hydroalcoholic solutions produced higher ellagitannin concentrations (5.9 %) compared to hot aqueous solutions (2.9 %). Based on these results, food-grade separation strategies are now being considered to further isolate and purify these compounds and enable more direct tasting. This approach makes it possible to taste and compare the main ellagitannins under controlled conditions, outside of the wine matrix. By combining green extraction techniques with sensory analysis, this work contributes to a better understanding of ellagitannins’ sensory properties and their relationship with wood composition, extraction methods, and wine aging.

References

1. Chira, K.; Teissedre, P.-L. (2013). Extraction of Oak Volatiles and Ellagitannins Compounds and Sensory Profile of Wine Aged with French Winewoods Subjected to Different Toasting Methods: Behaviour during Storage. Food Chem. 140 (1), 168–177.