Effects of rehydration nutrients on H(2)S metabolism and formation of volatile sulfur compounds by the wine yeast VL3

In winemaking, nutrient supplementation is a common practice for optimising fermentation and producing quality wine. Nutritionally suboptimal grape juices are often enriched with nutrients in order to manipulate the production of yeast aroma compounds. Nutrients are also added to active dry yeast (ADY) rehydration media to enhance subsequent fermentation performance. In this study we demonstrate that nutrient supplementation at rehydration also has a significant effect on the formation of volatile sulfur compounds during wine fermentations. The concentration of the 'fruity' aroma compounds, the polyfunctional thiols 3-mercaptohexan-1-ol (3MH) and 3-mercaptohexyl acetate (3MHA), was increased while the concentration of the 'rotten egg' aroma compound, hydrogen sulfide (H(2)S), was decreased. Nutrient supplementation of the rehydration media also changed the kinetics of H(2)S production during fermentation by advancing onset of H(2)S production. Microarray analysis revealed that this was not due to expression changes within the sulfate assimilation pathway, which is known to be a major contributor to H(2)S production. To gain insight into possible mechanisms responsible for this effect, a component of the rehydration nutrient mix, the tri-peptide glutathione (GSH) was added at rehydration and studied for its subsequent effects on H(2)S formation. GSH was found to be taken up during rehydration and to act as a source for H(2)S during the following fermentation. These findings represent a potential approach for managing sulfur aroma production through the use of rehydration nutrients.