Coupling EPR spin trapping of hydroxyethyl radicals and Strecker aldehydes analysis for predicting oxidative susceptibility of Chardonnay wines.

During white wine oxidation, the Fenton reaction involves ethanol oxidation to form 1-hydroxyethyl radicals (1-HER) and triggers a complex oxidative cascade that produces Strecker aldehydes (SA), particularly methional and phenylacetaldehyde. We quantified free and total SA by GC-MS in 50 Chardonnay wines with different oxidative status. 1-HER kinetics were monitored by spin trap/EPR and expressed by index a (related to kinetic curve area/width). On average, the free form accounted for 21 % (methional) and 51 % (phenylacetaldehyde) of their total forms, while bound fractions varied widely. In oxidized wines, total methional correlates with the accumulation of the free fraction, whereas index a correlates with free methional. These observations were confirmed under controlled accelerated aging (AAg) conditions. Initial bound methional content predicted increases in free methional, supporting its value as a marker of oxidative sensitivity. Furthermore, using two spin traps (POBN and DMPO) with distinct radical selectivity, we confirmed that both 1-HER and hydroxyl radicals are implicated in methional formation. Overall, these results provide an enological interpretation of an EPR signature of oxidative susceptibility and suggest that combining index a with free SO2 may predict the oxidative shelf life of Chardonnay wine.