OPTIMIZATION, VALIDATION AND APPLICATION OF THE EPR SPIN-TRAPPING TECHNIQUE TO THE DETECTION OF FREE RADICALS IN CHARDONNAY WINES
The aging potential of Burgundy chardonnay wines is considered as quality indicator. However, some of them exhibit higher oxidative sensitivity and premature oxidative aging symptoms, which are potentially induced by no-enzymatic oxidation such as Fenton-type reaction (Danilewicz, 2003). This chemical mechanism involves the action of transition metal, native phenolic compounds and oxygen which promote the generation of highly reactive oxygen species (ROS) such as hydroxyl radicals (OH) or 1-hydroxyethyl radicals (1-HER) from oxidation of ethanol. Such mechanism is involved in the radical oxidation occurring during bottle aging. According to Elias et al.,(2009a), the 1-HER is the most abundant radical in forced oxidation treated wines. Consequently, understanding its evolution kinetic in dry white wines is of great importance. Due to the reactivity (Danilewicz, 2003) and short half-life (10-6-10-9s) of ROS in aqueous solution (Pryor, 1986), their direct quantitation in wine is impossible. However, by means of spin-trapping technique, the radicals can form relatively stable adducts with spin-trap, and thus be monitored in real-time by electron paramagnetic resonance (EPR) (Elias et al., 2009b).
This study aims to optimize and validate an EPR spin trapping method using POBN as spin trap, to monitor the formation kinetic of 1-HER in chardonnay white wine and investigate the impact of some enological parameters (pH, ethanol, acidity, sulfites) on their formation. 1-HERs were generated by Fenton reaction (Fe²+ and H₂O₂) in chardonnay wines. The relative amount of reactant was optimized. In addition, several strategies were developed to decrease the impact of bisulfite on the detection of EPR signal. Finally, the analytical method was validated in terms of repeatability and reproducibility and applied to many chardonnay wines. To some extent, this study provides new insights into radical behavior that may contribute to comprehensive understanding of the oxidative stability of chardonnay white wines.
Issue: OENO Macrowine 2023
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chardonnay, radical, wine oxidation, EPR