Enhanced Enzymatic Release of Polyfunctional Thiols from Glutathionylated And/or γ-glucys-s Conjugates over Cysteinylated Precursors in Lager and Special Yeasts: Toward Novel Cofermentation Strategies

The enzymatic release of polyfunctional thiols (PFTs) from glutathionylated (G-) and cysteinylated (Cys-) precursors, mainly derived from hop, can significantly enhance the organoleptic properties of dry-hopped and NABLABs beers. S. cerevisiae yeasts are well-known for their high efficiency in releasing PFTs from Cys-adducts due to their strong β-lyase activity. The aim of this study was to explore the ability of S. pastorianus strains and other special yeasts to release PFTs from G- and the intermediate γ-GluCys-adducts. Fermentation trials were conducted over 7 days at 24°C, followed by 3 days of maturation at 4°C, using 15 °P unhopped wort spiked with different conjugates. Free thiol-specific extraction was performed using an Ag-ion SPE cartridge, followed by quantification via GC-PFPD. Our results bring strong evidence that some S. pastorianus yeasts exhibit β-lyase activity that directly breaks down the dipeptide γ-GluCys into free PFTs, while a few special yeasts show higher release efficiency directly from the tripeptide. Based on these findings, potential synergies between lager and ale yeasts are proposed to improve the release of free thiols.