ATTENTION/WARNING - NE PAS DÉPOSER ICI/DO NOT SUBMIT HERE

Ceci est la version de TEST de DIAL.mem. Veuillez ne pas soumettre votre mémoire sur ce site mais bien à l'URL suivante: 'https://thesis.dial.uclouvain.be'.
This is the TEST version of DIAL.mem. Please use the following URL to submit your master thesis: 'https://thesis.dial.uclouvain.be'.
 

Development of enzymatic tests to evaluate the γ-glutamyltranspeptidase activity of lager and ale yeasts involved in the release of free polyfunctional thiols from S-precursors

Loquet, Natacha
(2025)

Files

Loquet_13391900_2025.pdf
  • Closed access
  • Adobe PDF
  • 5.1 MB

Details

Supervisors
Collin, Sonia ; Christiaens, Romain
Faculty
Faculté des sciences
Degree label
Master [120] en biochimie et biologie moléculaire et cellulaire, à finalité spécialisée: biotechnologie
Abstract
The objective of this study was to complete the full evaluation of the enzymatic activities involved in the release of polyfunctional thiols (PFTs) from S-precursors. This research primarily focused on comparing the activity of γ-glutamyltranspeptidase (γ-GT) in lager (S. pastorianus), ale (S. cerevisiae) and in the special ale maltose-maltotriose-negative (S. cerevisiae var. chevalieri). Once these new results were obtained, the discussion focused on a global comparison of enzymatic activities based on previous studies. Firstly, the results demonstrate that the super lager yeasts thiol producers (BRAS-45 and E-30) initially utilise their carboxypeptidase (up to 41.541 A/h for E-30) to obtain the γ-glutamylcysteinylated precursors (γGluCys). Subsequently, a β-lyase releases free polyfunctional thiols (PFTs) directly with a release efficiency of up to 0.35 % for BRAS-45. Secondly, ale yeasts (K-97 and S-33) exhibit a distinct degradation pathway for glutathionylated (G-) precursors. These yeasts require both carboxypeptidase and γ-GT, with activities reaching up to 30.216 and 19.819 A/h respectively for K-97, to convert G-precursors into cysteinylated (Cys-) precursor. Finally, PFTs are released through the action of a β-lyase on Cys-precursors. Nevertheless, maltose-negative yeast LA-01 (S. cerevisiae var. chevalieri) employs a different degradation pathway, using a β-lyase directly on the tripeptide to release free PFTs. Finally, comparative tests were conducted to assess the contribution of γ-GT activity from both malt and yeast, determining which source significantly enriches wort’s γ-GT content. The results demonstrated that the optimal lager yeast contributed twice as much γ-GT as malt with 20.736 A/h compared to 9.708 A/h.