Abstract
Reactive compounds with one or more sulfane sulfur atoms can be an important source of reductive off-odors in wine. These substances contain labile sulfur, which can participate in microbiological (enzymatic) and chemical transformations (including in the post-bottling period), releasing malodorous hydrogen sulfide (H2S) and its derivatives (MeSH, EtSH, etc.). The following sulfane sulfur compounds were considered in this review as important precursors in the wine chemistry of reductive aromas: elemental sulfur (S8), persulfides (R-S-S-H), polysulfanes (R-Sn-R(′)), polythionates (−O3S-Sn-SO3−), thiosulfate (S2O32−) and derivatives of (poly)sulfane monosulfonic acids (R-Sn-SO3H). This review discusses the formation of these compounds, their reactivity and chemical transformations in wine, including reactions of nucleophilic substitution. In particular, the reactions of thiolysis, thiosulfatolysis and sulfitolysis of sulfane sulfur compounds are described, which lead in the end to reductive aroma compounds. In this way, the review attempts to shed light on some of the mysteries in the field of sulfur chemistry in wine and the reappearance of reductive off-odors after bottling.
Highlights
Hydrogen sulfide (H2 S) and its derivatives (MeSH, EtSH, etc.) are among the main molecules responsible for reductive defects in wine, providing distinctive odor of “rotten eggs”, “cooked cabbage”, “onion”, etc. [1]
Proteins can be found in wine from different sources: grapes, yeast and lactic acid bacteria metabolism, wine aging on lees, the protein fining process, etc. [102,103]
Comparing the composition of sulfite-treated wine with an untreated one, a dataset of more than 11,000 new sulfur-containing compounds was found [110]. This goes along with our knowledge about numerous reaction pathways of wine nucleophiles with all the sulfane sulfur compounds dealt with in this review. It was shown how sulfane sulfur compounds can act as latent precursors of reductive off-odors in wine, such as hydrogen sulfide (H2 S) and its derivatives, MeSH, EtSH, etc
Summary
Hydrogen sulfide (H2 S) and its derivatives (MeSH, EtSH, etc.) are among the main molecules responsible for reductive defects in wine, providing distinctive odor of “rotten eggs”, “cooked cabbage”, “onion”, etc. [1]. The compounds with reductive aromas can appear in wine during fermentation as by-products released by yeasts or after wine bottling due to chemical transformations of various precursors. This review is a continuation of our research to comprehend the phenomena of sulfur compounds in wine [13] based on recent studies When it comes to living organisms, the release of H2 S is closely related to its endogenous role as a small signaling molecule in different kinds of living matter. From the winemaking point of view, yeasts (e.g., Saccharomyces cerevisiae) with their metabolic pathways have a considerable impact on the character of wine They release ethanol and CO2 , but other substances in smaller quantities, including various sulfur compounds [17,18,19]. A description of sulfane sulfur precursors and a discussion of their importance; Possible reactions of chemicals and enzymatic formation of sulfane sulfur precursors, including the role of the sulfur metabolism of Saccharomyces cerevisiae yeasts; Chemical reactions and their mechanisms which lead to the formation of reductive off-odors in wine from sulfane sulfur precursors after bottling
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