Acetaldehyde
Correlation between Acetaldehyde perceived through tasting
and actual Acetaldehyde concentration
Gilis J-F., Cabri C. et Ducournau P.
Introduction
Micro-oxygenation consists in supplying micro doses of oxygen to wine, while avoiding oxygen accumulation, so as to favour certain oxidative reactions over others (LEMAIRE 1995, MOUTOUNET et al 2000). Polyphenols play an important role in red wines. In 1977, CHAPON proposed a reactional diagram showing the interaction of these compounds. Through oxidation, quinones or semi-quinonic radicals are formed, which live long enough to interact with other phenols in a "regenerator" polymerisation (SINGLETON, 1986).
In the same way, when a quinone is formed, another product of this reaction is peroxide; the indirect consequence of this is the oxidation of ethanol to acetaldehyde. (SINGLETON, 1978).
Several publications have described the role of acetaldehyde in polyphenol polymerisation. Dimers like catechin-ethyl-anthocyanin have been found (SAUCIER 1997). Besides the direct consequences on coloration linked to these anthocyanins, these reactions also affect the final molecular weight of the phenolic compounds in the wine.
Thus, in the presence of large quantities of monomeric anthocyanins, the reactions lead to a lower molecular weight. Acetaldehyde-induced polymerisation stops when the two ends of the chain are occupied by an anthocyanin (CHENIER et al 2000).
In practice, the carrying out of micro-oxygenation, especially in early stages, is partly determined by the gustatory and aromatic intensity of the acetaldehyde.
Figure 1 : Ethanol to acetaldehyde formation
Figure 2 : Catéchine-ethyl-anthocyane dimer
We have attempted to link the different levels of acetaldehyde perceived upon tasting, using a gas chromatographic analysis of compounds likely to be responsible for this perception.
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