In this master thesis, we aimed to adapt local isolates of the yeasts Saccharomyces cerevisiae and Lachancea thermotolerans for wort fermentation using directed evolution. The aim of the experiment was to improve the yeasts by eliminating catabolite repression with glucose in order to improve the consumption of maltose and maltotriose. Firstly, we optimised the parameters of mutagenesis for both yeast isolates. Based on these results, we performed mutagenesis with two mutagens, ethyl methanesulfonate and UV light. Then we cultivated these yeasts on the solid growth medium with the inhibitor of glucose catabolic pathway, 2-deoxyglucose, with which we established selective pressure. With both mutagens we successfully obtained mutants that were more resistant to the inhibitor and which presumably had preference for maltose. The second part of the experiment involved the selection and confirmation of the changed phenotype regarding maltose consumption of the mutants during wort fermentations and the chemical analyses of the beer samples with the high-performance liquid chromatography. We succeeded to obtain mutants that showed resistance to the inhibitor 2-deoxyglucose, abolished repression with glucose, and therefore also utilized maltose faster than the wild strains.
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