Varietal thiols have an impact on the overall aroma of many white, rosé, and red wines and beers. They originate from the metabolism of non-odorant aroma precursors by yeast during the fermentation step, via an intrinsic enzyme, the carbon-sulfur β-lyase (CSL, EC 4.4.1.13). However, this metabolism is directly dependent upon efficient internalization of aroma precursors and intracellular CSL activity. Consequently, the overall CSL activity converts on average only 1% of the total precursors available. To improve the conversion of thiol precursors during winemaking or brewing, we investigated the possibility of using an exogenous CSL enzyme from Lactobacillus delbrueckii subsp. bulgaricus produced in Escherichia coli. We first implemented a reliable spectrophotometric method to monitor its activity on different related aroma precursors and studied its activity in the presence of various competing analogues and at different pH values. This study allowed us to highlight the parameters to define CSL activity and structural insights for the recognition of the substrate, which pave the way for the use of exogenous CSL for the release of aromas in beer and wine.
Keywords: cysteine S-conjugates; varietal thiol precursors; wine aroma.