Blue-light photooxidation as a novel radical initiation method for EPR assessment of white wine oxidative stability

Abstract

Wine oxidation remains a major challenge for the wine industry, and robust tools to predict oxidative stability are still needed. Our group previously developed an EPR-based chemical oxidation assay to probe wine oxidative stability, relying on iron-catalysed Fenton initiation (Fe/H₂O₂) in the presence of the spin trap α-(4-pyridyl-N-oxide)-N-tert-butylnitrone (POBN) (1). Oxidative reactivity is monitored through the kinetics of the POBN–1-hydroxyethyl radical adduct (POBN–1-HER), enabling discrimination of wines according to oxidative stability (2). Coupling chemically initiated EPR with LC–MS metabolomic profiling further revealed the key contribution of sulfur-containing compounds to oxidative stability, providing mechanistic markers to support interpretation of EPR responses (3,4). Here, we introduce a Fenton-free radical initiation strategy based on blue-light photooxidation at 385 nm of white wine in the presence of POBN, using an external irradiation cell followed by EPR detection. The protocol was optimized with respect to irradiation time (5, 10 and 20 minutes), irradiation power (10 to 1000 W.m-2), and oxygen availability. Under the optimized conditions, 10 min irradiation at the selected blue-light power and a defined oxygenation state, radical formation was rapidly initiated and followed by a self-sustaining chain reaction. The resulting EPR spectrum displayed three doublets closely matching the POBN–1-HER signature obtained with chemical initiation, indicating similar radical pathways while avoiding the addition of chemical oxidants. The method was validated on 10 white wines from diverse French regions and benchmarked against our established chemical oxidation EPR assay. Photooxidation reproduced discriminating EPR responses relevant to oxidative stability classification. Overall, this work expands our EPR toolbox by establishing photooxidation as a controlled alternative to chemical initiation, while strengthening mechanistic insight into oxidative stability through complementary LC–MS profiling.

References

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