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AIMS: Some wine producers, in good years, can produce free-SO2 red wines and decide to add the minimum amount of sulphur dioxide only at bottling. To manage this addition, it is important to know the oxidative history of the wine. Acetaldehyde, the main wine oxidation product, is a powerful electrophile that reacts with numerous wine compounds giving desired products as the stable red polymeric pigments and the less astringent tannins but, also negative off-flavours. Although all these reactions are well known, the border between those increasing wine longevity and those decrementing wine quality is difficult to determine. This study has the aim to investigate the kinetics of consumption of acetaldehyde in red wines to give information useful for the further management of sulphur dioxide.
METHODS: Free-SO2 red wines were spiked with increasing levels of acetaldehyde (from 0 to 190 mg/L) and analysed over time. Chromatic properties and main phenolic classes were analysed by conventional spectrophotometric methods. Small phenolics, polymeric pigments (PP) and polymeric tannins (PT) were detected by HPLC, MS and NMR analysis. Reactivity of tannins towards BSA and saliva was also determined (1-2-3).
RESULTS: Already two hours after the addition of acetaldehyde the 50% was consumed in reactions with phenolic compounds and the consumption increased over time. Also when a great excess of aldehyde was added (190 mg/L) and after one year of aging a loss of 75% of the initial value was detected.
The first compounds that were consumed in reactions with acetaldehyde were anthocyanins and flavanols and a contemporary increase of polymeric pigments and tannins occurred. BSA and saliva reactive tannins increased over time when high concentration of acetaldehyde were added.
CONCLUSIONS: For a correct management of sulphur dioxide when bottling a free-SO2 red wine the content of acetaldehyde and phenolic strong reactants (anthocyanins and flavanols) should be determined to limit or favour further acetaldehyde reactions.
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