Evaluation of the hydroxyethyl radical formation kinetic and Strecker aldehydes distribution for assessing the oxidative susceptibility of Chardonnay wines

Abstract

Over the last decade, much attention has been paid on the oxidative susceptibility of white wines, given its key role in determining their ageing potential. Some wines may undergo premature oxidative ageing, during which the oxidative cascade can trigger the formation of hydroxyl radicals producing 1-hydroxyethyl radicals (1-HER) [2] and Strecker aldehydes (SA), such as methional and phenylacetaldehyde [1]. To date, the potential relationship between SA and the kinetics of 1-HER formation (K1-HER) is poorly documented.

The electron paramagnetic resonance (EPR) technique, dedicated for radical analysis, has been used in enological studies [3], [4]. Based on the literature, we recently proposed an optimized version of the EPR-spin trap approach to study K1-HER in Chardonnay wines [6]. New indexes derived from a log-normal model of kinetic curve were proposed. These analytical indexes were validated in terms of repeatability and reproducibility (RSD < 8 %). In parallel, a strategy inspired from literature [5] was slightly modified to analysis free and total SA (methional and phenylacetaldehyde) by SPE-GC-MS.

In a first experiment we analyzed twenty young commercial Chardonnay wines (2019-2022) from various appellations. Total and free methional levels ranged from 4-40 μg/L and 0.1-3 μg/L, respectively, whereas the bounded form represented 60 to 90% of the total methional content. Distinct EPR signatures were obtained allowing us to classify the wines according to their EPR signals and the SA content.

Additional slow oxidation experiments carried out in controlled conditions with different stoppers showed that after, at least six years of bottle aging, wines with a higher EPR index (≥30%) tended to exhibit elevated levels of both free and total methional. Finally, the EPR approach was applied on young wines made from grapes harvested at four ripening levels. Microvinifications (50 L, n=3) were carried out at the BIVB located in Burgundy. The first results showed the impact of the maturity level of the grapes on the capacity of young white wines to produce free radicals and SA. Although these results suggest that the EPR index may serve as a reliable predictor of wine susceptibility to oxidation, additional experiments will be carried out to validate these observations.

References

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[2] R. J. Elias et A. L. Waterhouse, J. Agric. Food Chem. (2010)

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[5] P. Grant-Preece, H. Fang, L. M. Schmidtke, et A. C. Clark, Food Chem. (2013)

[6] P. Han, and A. Pons, Food Chem. (in press.)