Persistence of wine polysulfides: Investigation of the stability of isolated glutathione and cysteine species

Recent studies have highlighted that polysulfides formed from biological thiols (e.g., glutathione, GSH) and sulfhydryls like H₂S may act as reservoirs of undesirable sulfur-like odours (SLOs) in wine, although the conditions leading to appearance of SLOs are not fully understood. The reactivity of polysulfides was investigated in aqueous solutions, focusing on the stability and behaviour of GSH polysulfides (up to six sulfur atoms) and mixed cysteine (Cys) and GSH polysulfides (up to four sulfur atoms). Polysulfides were prepared and isolated via semi-preparative HPLC and studied at different temperatures (25, 35, and 40 °C) to investigate their dynamic behaviour. Results revealed that higher temperatures did not necessarily accelerate the degradation of polysulfides; longer-chain GSH pentasulfide and hexasulfide, as well as the mixed Cys-GSH trisulfide and tetrasulfide, were relatively stable. However, storing samples at -20 °C and subsequent defrosting affected all polysulfides. Initial polysulfide concentrations also appeared to influence degradation over time.