Formation and fate of positive and negative sulfur compounds


Summary

Objective

What are the precursors for and formation and fate of the main volatile sulfur compounds in wine?

What is the influence of yeast strain on these compounds, what genes are involved and how are they regulated?

Background

Volatile sulfur compounds play an important role in the sensory experience of wines. While many of the compounds have been identified, there is little understanding of the origins or evolution of most of them or the conditions that facilitate these transformations.

Research approach

Four volatile sulphur compounds, hydrogen sulphide (‘rotten eggs’), methanethiol (‘sewage’), dimethyl suphide (‘blackcurrant’ or ‘truffle’ at low levels and  ‘canned corn’ or ‘cabbage’ at higher levels ) and phenylmethanethiol (‘struck flint’) make up the majority of negative volatile sulfur compounds found in wine and will be the focus of this project.

Isotope labelled precursors will be used to follow the formation and fate of these compounds in model studies. Wine studies will follow to confirm the model study results. The role of copper and other metals in their formation and fate will be investigated through winemaking trials and by identifying ligands (a functional group that binds to a central metal atom to form a coordination complex) to specifically bind different copper species.

The microbiology part of the plan addresses the role of yeast in the formation of volatile sulfur compounds. An over-expression library of genes from an enzyme class likely to be involved, pyridoxal phosphate dependent enzymes, will be used to identify important genes. Their role will be confirmed by making deletion mutants. Finally, the expression of the identified genes will be determined during winemaking.

Sector benefits

Knowledge generated in this project will lead to the development of practical strategies in winemaking to manipulate and control the levels of these volatile sulphur compounds during winemaking and bottle storage. These strategies would allow winemakers to tailor wine style and avoid negative aromas.