Characterization of Hydrogen Sulfide Formation in Commercial and Natural Wine Isolates ofSaccharomyces

Hydrogen sulfide production was investigated in 29 strains of Saccharomyces cerevisiae — two commercial and 27 natural isolates. Sulfide formation was evaluated under two synthetic juice conditions: one leading to full expression of the sulfate reduction sequence and the other to maximal repression of this pathway. Strains could be categorized as high, medium, low, or non-producers under each of these conditions. There was no correlation between category of production in these two media for the strains evaluated, but for each strain, production under repressing conditions was much less. Under repressing conditions, H2S production decreased from 4- to 560-fold depending upon the strain, with the majority of strains displaying a 200-fold or greater reduction in production. Hydrogen sulfide formation was also evaluated in natural and synthetic juices that establish conditions intermediate between full repression and induction of the sulfate reduction sequence, and with sulfur dioxide or with limitation for other components. Yeast variability in H2S formation was greatest under conditions of marginal nitrogen content of the medium, but there was not a simple correlation of amount of H2S formed and total nitrogen content, fermentation rate, or time of formation during fermentation. The effectiveness of nitrogen (diammonium phosphate) addition in commercial isolate UCD522 was found to be dependent upon the concentration of methionine in the medium. The effectiveness of methionine addition at suppression of hydrogen sulfide formation was similarly dependent upon the ammonium (or total nitrogen) content. At low methionine concentrations, DAP impact on H2S was minimal, and at low ammonium concentrations the effect of methionine addition was likewise minimal. Genetic analysis of one strain revealed that hydrogen sulfide formation is under the control of several genes, consistent with what is known about the complex regulation of the sulfate reduction pathway.