In this project we investigated two aspects of Brettanomyces bruxellensis wine spoilage: 1) production of 4-ethyl catechol, 4-ethyl guaiacol, and 4-ethyl phenol in model wine media; 2) enzymatic activity of volatile phenols production. Both studies were carried out with nine strains of B. bruxellensis isolated from wine. A larger amount of p-coumaric acid was metabolized when added alone to the model wine. When all the ethyl phenol precursors were added together a high amount of 4-ethyl guaiacol (from ferulic acid) was produced. Caffeic acid was metabolized at the lowest rate. This fact was confirmed by the lower enzymatic activity recorded in whole cell when caffeic acid was added as substrate. Three strains produced a much lower amount of ethyl phenol, and ethyl guaiacol, consuming only about 60 and 50%of the correspondent precursor respectively. However, when the hydroxycinnamic acids were added alone, only one of the three strains still produced a low amount of ethylphenols. The same strain also showed the lower enzymatic activity in whole cells when p-coumaric acid was added as substrate.
This research allowed us to highlight how not only Brettanomyces phenotype play an important role in the volatile phenol off-flavor production but also the media composition will contribute to the off flavor intensity. For more details, especially in relation to caffeic acid metabolism and cell density, further investigations are necessary.