Factors affecting the production of 4-ethylphenol by the yeast Dekkera bruxellensis in enological conditions

Abstract

The conversion of p-coumaric acid into 4-ethylphenol was studied in Dekkera bruxellensis ISA 1791 under defined conditions in synthetic media. The production of 4-ethylphenol occurred roughly between mid-exponential growth phase and the beginning of the stationary phase. This behaviour was observed when glucose was the only energy and carbon source, the conversion rate being close to 90%. Ethanol, as the single energy source, yielded conversion rates close to 80% while in the presence of trehalose and acetic acid conversion rates lower than 10% were obtained. The production of 4-ethylphenol was not observed when the cells were maintained in buffer solution without carbon and energy sources. The precursor of 4-ethylphenol, p-coumaric acid, was not utilized as energy and carbon source. Furthermore, it was shown that 4-vinylphenol may be used as a precursor of 4-ethylphenol in the absence of p-coumaric acid. Growth and 4-ethylphenol production were inhibited by increasing concentrations of ethanol, being fully prevented at 13% (v/v) ethanol. The cultivation of strain ISA 1791 in mixed culture with Saccharomyces cerevisiae, in synthetic medium, showed that the cell numbers of D. bruxellensis increased from 10 4 cfu/ml to 5×10 9 cfu/ml. Laboratory microvinifications of white and red juices inoculated with as low as 10 cfu/ml of D. bruxellensis and 10 7 cells/ml of S. cerevisiae showed growth of D. bruxellensis to levels of about 5×10 8 cfu/ml. In addition, 4-ethylphenol production by D. bruxellensis was observed only after complete fermentation of the grape juices.