The Effect of Nitrogen Deficiency and Sulfur-Containing Amino Acids on the Reduction of Sulfate to Hydrogen Sulfide by Wine Yeasts

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Abstract
The formation of hydrogen sulfide in wine has been shown to arise from fermentations of grape musts with nitrogenous deficiencies. This work was instigated to explore this formation with the use of a qualitative, but simple, rapid, and explicit method for hydrogen sulfide detection. Two yeast strains were used that showed representative high and low formations of sulfide from sulfite. In synthetic medium, without added sulfite, the formation of hydrogen sulfide was shown to come exclusively from reduction of sulfate and was dependent upon the limiting concentration of ammonia. The amount of n-propanol formed was also found to be dependent upon the yeast strain and upon the ammonia present. Under ammonia limitations, the addition of non-sulfur containing amino acids tended to inhibit the formation of hydrogen sulfide from sulfate but increased formation of sulfite. Added cysteine brought about increased sulfide but inhibited sulfite formation. Added methionine inhibited both sulfide and sulfite formation, as expected. These results, while preliminary, show that sulfate can be the main substrate for hydrogen sulfide production. The amount of n-propanol formed was explained by metabolic control by methionine.

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