Role of p-Coumaric Acid and Micronutrients in Sulfur Dioxide Tolerance in Brettanomyces bruxellensis

Sulfite is a common preservative in wine, but the spoilage yeast Brettanomyces bruxellensis can produce volatile phenols even with the recommended sulfite dose. The purpose of this study was to examine how wine components, p-coumaric acid (a precursor of volatile phenols), and micronutrients influence culturability, viability, and volatile phenols production by B. bruxellensis under sulfite stress. In red wine, a high sulfite dose (potassium metabisulfite, 100 mg L−1) led to an immediate death phase followed by growth recovery after two weeks. However, 4-ethylphenol (4-EP) was continuously produced by dead or nonculturable cells. Nonetheless, an event of growth recovery could not be observed in the case of the model wine. However, when the model wine was supplemented with minerals and vitamins, both growth recovery and 4-EP production were noticed, suggesting that the minerals and vitamins played an important role in maintaining the viability of cells under the sulfite stress. The yeast could also utilize the p-coumaric acid (p-CA) as an energy source, showing a specific growth rate of 0.0142 h−1 with 1 mM of p-CA in model wine. Furthermore, the sulfite-stressed cells exhibited ATP production by means of proton efflux while utilizing the p-CA. This work highlights the novel finding that the conversion of p-CA into 4-EP provides sufficient energy for the cell to remain metabolically active under the sulfite stress.