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Applied and Environmental Microbiology, January 2008, p. 454-461, Vol. 74, No. 2
0099-2240/08/$08.00+0     doi:10.1128/AEM.01616-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Parameters Affecting Ethyl Ester Production by Saccharomyces cerevisiae during Fermentation{triangledown}

S. M. G. Saerens,1,2,3* F. Delvaux,1 K. J. Verstrepen,1,4 P. Van Dijck,2,3 J. M. Thevelein,2,3 and F. R. Delvaux1

The Centre for Food and Microbial Technology, Department of Microbial and Molecular Systems, Katholieke Universiteit Leuven, Kasteelpark Arenberg 22, B-3001 Heverlee, Belgium,1 Laboratory of Molecular Cell Biology, Institute of Botany and Microbiology, Katholieke Universiteit Leuven, Kasteelpark Arenberg 31, B-3001 Heverlee, Belgium,2 Department of Molecular Microbiology, VIB, Katholieke Universiteit Leuven, B-3001 Heverlee, Belgium,3 FAS Center for Systems Biology, Harvard University, 7 Divinity Avenue, Cambridge, Massachusetts 021384

Received 16 July 2007/ Accepted 29 October 2007

Volatile esters are responsible for the fruity character of fermented beverages and thus constitute a vital group of aromatic compounds in beer and wine. Many fermentation parameters are known to affect volatile ester production. In order to obtain insight into the production of ethyl esters during fermentation, we investigated the influence of several fermentation variables. A higher level of unsaturated fatty acids in the fermentation medium resulted in a general decrease in ethyl ester production. On the other hand, 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. Together with the previous demonstration that provision of medium-chain fatty acids, which are the substrates for ethyl ester formation, to the fermentation medium causes a strong increase in the formation of the corresponding ethyl esters, this result further supports the hypothesis that precursor availability has an important role in ethyl ester production. We concluded that, at least in our fermentation conditions and with our yeast strain, the fatty acid precursor level rather than the activity of the biosynthetic enzymes is the major limiting factor for ethyl ester production. The expression level and activity of the fatty acid biosynthetic enzymes therefore appear to be prime targets for flavor modification by alteration of process parameters or through strain selection.

* Corrresponding author. Mailing address: Centre for Food and Microbial Technology, Department of Microbial and Molecular Systems, Katholieke Universiteit Leuven, Kasteelpark Arenberg 22, B-3001 Heverlee, Belgium. Phone: 32(0)16329627. Fax: 32(0)16321576. E-mail: Sofie.Saerens{at}biw.kuleuven.be

{triangledown} Published ahead of print on 9 November 2007.

Applied and Environmental Microbiology, January 2008, p. 454-461, Vol. 74, No. 2
0099-2240/08/$08.00+0     doi:10.1128/AEM.01616-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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