Are dicysteinyl polysulfanes responsible for post-bottling release of hydrogen sulfide?

Abstract

Hydrogen sulfide (H2S) has a significant impact on wine aroma attributes and wine quality when present at concentrations above its aroma threshold of 1.1 to 1.6 μg/L. Therefore, the management of H2S concentrations in wines, whether from fermentation or “other” origins, is an important consideration for winemakers. The main techniques used for H2S removal are oxidative handling and/or copper fining; however, the effectiveness of these treatments may be temporary, as H2S can often reappear post-bottling along with other volatile sulfur compounds (VSCs) when reductive conditions are re-established. Moreover, it is proposed that oxidative treatments applied in the presence of copper may produce compounds such as disulfides and diorganopolysulfanes, which might initially appear stable but are susceptible to reductive cleavage, thereby potentially acting as latent sources of H2S. 

The aim of this study was to determine whether putative polysulfanes could act as latent sources of H2S during post-bottling storage. Experiments conducted in model wine enabled identification of four dicysteinyl polysulfanes when H2S was oxidised in the presence of cysteine, copper and iron. The stability of the dicysteinyl polysulfanes formed in-situ was evaluated and conditions impacting the release of H2S from the polysulfanes were also determined, which provided some understanding of the possible mechanisms of release. 

The results of this study showed that the stability of the dicysteinyl polysulfanes decreased as sulfur chain length increased, which accorded with the relative proportions of polysulfanes initially formed. 

Notably, H2S was released over time, with the greatest decline in polysulfane relative abundance and largest release of H2S (up to 212 μg/L) being associated with the addition of commonly used reducing agents, especially sulfur dioxide, to the model wines containing the polysulfanes. Desulfurisation of cysteine could account for only minor quantities of H2S. In addition, Cysteine-S-sulfonates were tentatively identified by mass spectrometry after six months of storage, and similarly to the parent polysulfanes, their relative concentrations decreased with increasing number of linking sulfur atoms. These results shed light on the potential pathways for reformation of VSCs in bottled wine and demonstrate that dicysteinyl polysulfanes may have the potential to act as latent sources of H2S in wine post-bottling, potentially via a sulfitolysis mechanism.