Improvement of aromatic thiol release through the selection of yeasts with increased β-lyase activity

• The selective SMC medium is a useful tool for the isolation of β-lyase active yeasts.
• SMC medium was useful to discriminate among S. cerevisiae IRC7 genotypes.
• 9.4% of wild S. cerevisiae isolates were heterozygous for IRC7 gene.
• T. delbrueckii showed a similar β-lyase activity to full-length IRC7 strains.

The development of a selective medium for the rapid differentiation of yeast species with increased aromatic thiol release activity has been achieved. The selective medium was based on the addition of S-methyl-l-cysteine (SMC) as β-lyase substrate. In this study, a panel of 245 strains of Saccharomyces cerevisiae strains was tested for their ability to grow on YCB-SMC medium. Yeast strains with an increased β-lyase activity grew rapidly because of their ability to release ammonium from SMC in comparison to others, and allowed for the easy isolation and differentiation of yeasts with promising properties in oenology, or another field, for aromatic thiol release. The selective medium was also helpful for the discrimination between those S. cerevisiae strains, which present a common 38-bp deletion in the IRC7 sequence (present in around 88% of the wild strains tested and are likely to be less functional for 4-mercapto-4-methylpentan-2-one (4MMP) production), and those S. cerevisiae strains homozygous for the full-length IRC7 allele. The medium was also helpful for the selection of non-Saccharomyces yeasts with increased β-lyase activity. Based on the same medium, a highly sensitive, reproducible and non-expensive GC–MS method for the evaluation of the potential volatile thiol release by different yeast isolates was developed.