engleski

Functional analysis of ethyl esters genes in the Saccharomyces genus

In recent years, yeast functional genomics and metabolic engineering has been applied successfully for the improvement of various fermentation processes. The most important role in this processes have S .cerevisiae, S. bayanus, recently S. paradoxus and some hydride species. The use of functional genomics is indispensable understand the synthesis of different compounds during fermentation, like ethyl esters. In the presented research we characterized in detail genes involved in the production of ethyl esters during alcoholic fermentation in two different species, S.cerevisae and S.paradoxus. Since ethyl esters have significantly positive effect on wine aroma formation, after fermentations conducted in chemically defined and natural musts, we have isolated two yeasts (one S.cerevisiae and one S.paradoxus), which synthesize higher concentrations of mentioned compounds. In the chosen yeast species we identify the genes, which are responsible for ethyl esters synthesis (ETH 1 and EEB 1). In both species at DNA level the genes demonstrated almost 92% of similarity in the case of EHT1 and 96% in the case of EEB1. Further we have analyzed the level of expression of the investigated genes in different conditions. The two species showed similar pattern regarding ethyl ester synthesis. A higher fermentation temperature resulted in greater ethyl octanoate and decanoate production, while a higher carbon or nitrogen content of the fermentation medium resulted in only moderate changes in ethyl ester production. Analysis of the expression of the ethyl ester biosynthesis genes EEB1 and EHT1 after addition of medium-chain fatty acid precursors suggested that the expression level is not the limiting factor for ethyl ester production, as opposed to acetate ester production. We concluded that, at least in our fermentation conditions and with our yeast strains, the fatty acid precursor level rather than the activity of the biosynthetic enzymes is the major limiting factor for ethyl ester production, and we do not identify any differences in S.cerevisiae and S.paradoxus.

S.cerevisae; S.paradoxus; ethyl esters

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