Brine-Releasable Hydrogen Sulfide in Wine: Mechanism of Release from Copper Complexes and Effects of Glutathione.

Copper-sulfhydryl complexes in wine can be disrupted by addition of brine to release free hydrogen sulfide (H ₂ S), and the resulting "brine-releasable H ₂ S" is reported to correlate with formation of H ₂ S during bottle storage. However, both the mechanism of the brine-release assay and factors affecting the stability of copper sulfhydryls under brine-release conditions are not well understood. By varying brine composition and concentration, it is shown that release of copper-complexed H ₂ S requires the presence of a halide (Cl ^- and Br ^- ) and is not due to a general "salting-out" effect. Release of copper-complexed H ₂ S by the brine dilution assay is highly temperature-dependent. When H ₂ S and Cu(II) are added to a model wine, brine-releasable H ₂ S decreases markedly (∼10-fold) after a 20 min incubation period prior to performing the brine-release assay. In commercial wines, the fraction of added H ₂ S recovered through the brine-release assay was correlated with the initial glutathione (GSH) concentration ( r ² = 0.58) but not with initial Cu. Negligible additional release of H ₂ S from organopolysulfanes was observed following addition of a disulfide-reducing agent (tris(2-carboxyethyl)phosphine). As previous studies have reported a correlation between H ₂ S formed under brine-release conditions and normal storage, these results suggest that the susceptibility of a wine to form latent copper-sulfhydryl precursors of H ₂ S following copper addition is dependent on the concentration of sulfhydryls like GSH.