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Influence of Polyphenolic Components of Red Wines on the Microbial Synthesis of Volatile Phenols

The capacity of lactic acid bacteria such as Pediococcus damnosus, Lactobacillus plantarum , and Leuconos- toc oenos to form volatile phenols was studied in comparison with Saccharomyces cerevisiae and Brettano- myces bruxellensis in various culture conditions. Lb. plantarum was the only bacterium capable of forming notable quantities of 4-ethylphenol, a volatile phenol with a disagreeable odor of "wet horse". However, these quantities were lower than those produced by B. bruxellensis . When Lb. plantarum was cultivated in a standard medium enriched with certain polyphenolic compounds, or seeded directly in a red wine, the quantity of volatile phenols synthesized by these bacteria decrease highly. This decrease was even more significant at higher concentrations of procyanidic tannins. A major decrease in the 4-ethylphenol synthesis was observed at concentrations upwards of 1 g/L procyanidin. On the other hand, the synthesis of volatile phenols by B. bruxellensis was not affected in any way by the presence of the polyphenolic compounds found in red wines. These results confirmed that yeasts of the genus Brettanomyces/Dekkera sp. were responsible for the "phenolic character" of red wines previously described. In fact, these are the only microorganisms capable of synthesizing, in the presence of tannins, the high quantities of ethylphenols responsible for this particular off- flavor.