# Electron paramagnetic resonance (EPR) spin trapping applied to Chardonnay wines: impact of phenolic content and ethanol

## TL;DR

This study uses a specialized EPR technique to analyze how Chardonnay wines age, focusing on radical oxidation and how wine components like phenolics and ethanol influence this process.

## Contribution

The first application of a log-normal model to describe 1-hydroxyethyl radical formation kinetics in wine using EPR spin trapping.

## Key findings

- A thermo-accelerated EPR method was optimized for analyzing radical oxidation in Chardonnay wines.
- Low phenolic acid levels, especially cinnamic acids like caftaric acid, correlate with specific 1-HER formation kinetics.
- Ethanol concentration within the typical wine range (12–15% vol.) does not significantly affect 1-HER formation.

## Abstract

Chemical oxidation is the main cause of damage during the bottle aging of white wines. It is due to Fenton-type reaction mechanisms, i.e., a radical oxidation cascade which leads to the formation of 1-hydroxyethyl radicals (1-HER) from ethanol. An optimized electron paramagnetic resonance (EPR) approach, using the Fenton reaction and N-tert-Butyl-α-(4-pyridyl-1-oxide) nitrone as spin trap, was used to study the formation kinetic of 1-HER. Important parameters of the reaction were identified and optimized, i.e., temperature, dissolved oxygen and free bisulfite content. We found that acetaldehyde removed bisulfite without artifacts on 1-HER kinetics, making the protocol suitable for routine laboratory analysis. We then validated the log-normal model to describe the complex formation/degradation kinetic of 1-HER and used it to rank 69 Chardonnay wines in four categories. Low levels of phenolic acid, in particular the cinnamic acids such as caftaric acid, seemed to correspond to a specific formation kinetic of 1-HER (high level produced slowly). In addition, ethanol concentration (0–100 % vol.) greatly impacted its formation kinetics, whereas it had non-significant effect within the white wine range (12–15 % vol.). These results demonstrate that the response of white wines to radical oxidation in controlled and tuned conditions is a promising approach to evaluate aging potential and suggest that maturity level might modulate the 1-HER formation in Chardonnay wines.

Image 1

•Thermo-accelerated technique to improve EPR analyses in wine.•Validation of chemical removal of bisulfite for 1-HER analysis by EPR.•First application of log-normal index on 1-HER kinetic study.•1-HER kinetic classification associated with phenolic composition differences.•No effect of ethanol level of wine (12–15 % vol. range) on EPR signal.

Thermo-accelerated technique to improve EPR analyses in wine.

Validation of chemical removal of bisulfite for 1-HER analysis by EPR.

First application of log-normal index on 1-HER kinetic study.

1-HER kinetic classification associated with phenolic composition differences.

No effect of ethanol level of wine (12–15 % vol. range) on EPR signal.