Clues about the role of methional as character impact odorant of some oxidized wines

A young white wine that had undergone spontaneous oxidation and showed a st rong off-flavor reminiscent of cooked vegetables was demixed by salting out to obtain an ethanolic extract that retained the off-flavor of the wine, a s was demonstrated by sensory analysis. This extract, together with a secon d one obtained from a non-oxidized wine sample, were chromatographed into a reversed-phase HPLC column using a water/ethanol gradient. The column effl uents were collected in 14 different fractions that were evaluated for smel l. Four fractions were found to differ between oxidized and non-oxidized wi ne, but only one showed a clear cooked vegetables off-flavor and, when adde d to a non-oxidized wine, made it significantly more similar to the oxidize d wine. The fraction was analyzed by GC-MS-olfactometry, which made it poss ible to identify methional as the single important odorant of the fraction. The odor threshold of methional in a synthetic wine was found to be 0.5 mu g L-1. The analytical determination of methional through GC-FPD in several oxidized and non-oxidized wines showed that, in the former, methional can reach more than 200 Odor Units, whereas in the non-oxidized samples, it was not possible to detect methional. The methional concentration was found to increase in wines spiked with both methionol or methionine, which suggests that it can be formed from direct peroxidation of methisnol or via Strecke r degradation of methionine mediated, probably, by o-quinones formed during wine oxidation.