Identification and quantification of molecular ellagitannins in cognac eaux-de-vie by a mass spectrometry method: barrel toasting and aging impact

Abstract

AIM: Ellagitannins are the main oak wood phenolic compounds that contribute to wine and spirits organoleptic quality (color, astringency, bitterness)(1-3). Given the lack of knowledge regarding their composition and evolution in spirits, the objectives were to follow their extraction kinetic in Cognac “eaux-de-vie” matured in barrel representing different toasting and to observe their evolution and structural modifications during aging.

METHODS: Eight different toasting levels were used for studying the impact of the toasting on ellagitannins composition. Two verticals (1978-2018) of “eaux-de-vie” samples coming from two terroirs were analyzed in order to observe ellagitannins evolution during aging. The above analyses were conducted using HPLC-Triple Quadrupole mass spectrometer (4) and the unknown compounds were identified by UPLC-Q-TOF, purified by preparative HPLC prior to 1D/2D-NMR analysis.

RESULTS: A general trend between the toasting levels and the individual ellagitannins content and composition was observed. Indeed “Eau-de-vie” aged in light toasted barrel has 40% higher castalagin content than in high toasting. During spirit aging, native ellagitannins content decreases over time. After two years, only castalagin remains quantifiable, suggesting that they undergo transformations leading to the formation of new compounds. Among them, whisky tannin B and A ([M-H]- ion peak at m/z 977.0896 and m/z 675.0834 respectively), resulting from the ethanol/castalagin or castalin reaction as well as some ellagitannin oxidation products like dehydrocastalagin and dehydroroburin D were identified for the first time in Cognac “eaux-de-vie” samples. The kinetic of the above compounds is in progress and the influence of both aging and barrel toasting is being researched.

CONCLUSIONS:

This work brings new insights on the Cognac ellagitannins content and how these molecules are influenced by aging and barrel toasting. Tastings will be performed to understand the organoleptic impact of these compounds.