Phenolic compounds are among of the most important flavor and aroma molecules in beer, where their concentration ranges from 500 to 1000 mg/L, and is made of several different phenol groups. 70-80% of phenolic compounds are derived from malt and 20-30% are derived from hops. During the process of fermentation they are susceptible to biotransformation. Among the brewing yeast the enzymatic transformation of volatile phenols is researched more into detail. It mainly refers to the transformation of hydroxycinnamic acids, e.g. transformation of ferulic and p-cumaric acid, to 4-vinylguaiacol and 4-vinylphenol. Transformation is catalysed by ferulic acid decarboxylase (FDC1) and phenylacrylic acid decarboxylase (PAD1). Besides hydroxycinnamic acids, other phenolic compoudns like simple phenols, benzoic acid derivatives, coumarins, proanthocyanidins, chalcones and flavonoids, can be found in beer. Some of those are present in relatively high concentrations, e.g. tyrosol, p-hydroxybenzoic acid, vanillic acid, vanillin, catechin and epicatechin, dimeres of proantocianidin and isoxanthohumol. The goal of this thesis is to understand the proces of beer fermentation, beer composition, the evolution and evolutionary differences between different yeast strains, their role in metabolism of phenolic compounds and also get to know the techniques that help us improve the industrial yeast strains.
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