Role of Elemental Sulfur in Forming Latent Precursors of H₂S in Wine

The level of hydrogen sulfide (H₂S) can increase during abiotic storage of wines, and potential latent sources of H₂S are still under investigation. We demonstrate that elemental sulfur (S⁰) residues on grapes not only can produce H₂S during fermentation but also can form precursors capable of generating additional H₂S after bottle storage for 3 months. H₂S could be released from S⁰-derived precursors by addition of a reducing agent (TCEP), but not by addition of strong brine to induce release of H₂S from metal sulfide complexes. The size of the TCEP-releasable pool varied among yeast strains. Using the TCEP assay, multiple polar S⁰-derived precursors were detected following normal-phase preparative chromatography. Using reversed-phase liquid chromatography and high-resolution mass spectrometry, we detected an increase in the levels of diglutathione trisulfane (GSSSG) and glutathione disulfide (GSSG) in S⁰-fermented red wine and an increase in the levels of glutathione <i>S</i>-sulfonate (GSSO₃^–) and tetrathionate (S₄O₆^2–) in S⁰-fermented white wine as compared to controls. GSSSG, but not S₄O₆^2–, was shown to evolve H₂S in the presence of TCEP. Pathways for the formation of GSSSG, GSSG, GSSO₃^–, and S₄O₆^2– from S⁰ are proposed