SYNTHESIS OF VOLATILE PHENOLS BY SACCHAROMYCES-CEREVISIAE IN WINES

Vinylphenols (4-vinylphenol and 4-vinylguaiacol) are natural constituents of wine and can play a role in wine aroma. However, only white wines contain important quantities of these volatile substances which, beyond a certain concentration (limit threshold = 725 mug litre-1 of 4-vinylguaiacol + 4-vinylphenol (1:1)), can be responsible for a depreciating 'phenolic' or 'pharmaceutic' characteristic. Saccharomyces cerevisiae possesses a type-(E) enzymic activity, substituted cinnamate carboxy-lyase (SCD), which is capable of transforming, by non-oxidative decarboxylation, the phenolic acids in the must, (E) p-coumaric and (E) ferulic acids, into corresponding vinylphenols. This endocellular activity is constitutive, it is only expressed during alcoholic fermentation and with a variable intensity depending on the yeast strain. Furthermore, the enzyme is rapidly inhibited by catechic tannins, which explains why, in comparison with white wines, red and rose wines contain low levels of vinylphenols despite having more precursors. A yeast strain with a weak SCD activity has been selected and its use in vinification should eliminate the appearance of the phenolic taint in white wines coming from grapes rich in decarboxylable hydroxycinnamic acids.