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Applied and Environmental Microbiology, February 2000, p. 744-753, Vol. 66, No. 2
Institute for Wine Biotechnology and
Department of Viticulture and Oenology, University of Stellenbosch,
ZA-7600 Stellenbosch, South Africa
Received 16 August 1999/Accepted 12 November 1999
The distinctive flavor of wine, brandy, and other grape-derived
alcoholic beverages is affected by many compounds, including esters
produced during alcoholic fermentation. The characteristic fruity odors
of the fermentation bouquet are primarily due to a mixture of hexyl
acetate, ethyl caproate (apple-like aroma), iso-amyl acetate
(banana-like aroma), ethyl caprylate (apple-like aroma), and
2-phenylethyl acetate (fruity, flowery flavor with a honey note). The
objective of this study was to investigate the feasibility of improving
the aroma of wine and distillates by overexpressing one of the
endogenous yeast genes that controls acetate ester production during
fermentation. The synthesis of acetate esters by the wine yeast
Saccharomyces cerevisiae during fermentation is ascribed to
at least three acetyltransferase activities, namely, alcohol
acetyltransferase (AAT), ethanol acetyltransferase, and iso-amyl AAT.
To investigate the effect of increased AAT activity on the sensory
quality of Chenin blanc wines and distillates from Colombar base wines,
we have overexpressed the alcohol acetyltransferase gene
(ATF1) of S. cerevisiae. The ATF1
gene, located on chromosome XV, was cloned from a widely used
commercial wine yeast strain of S. cerevisiae, VIN13, and
placed under the control of the constitutive yeast phosphoglycerate
kinase gene (PGK1) promoter and terminator. Chromoblot
analysis confirmed the integration of the modified copy of
ATF1 into the genome of three commercial wine yeast strains (VIN7, VIN13, and WE228). Northern blot analysis indicated constitutive expression of ATF1 at high levels in these yeast
transformants. The levels of ethyl acetate, iso-amyl acetate, and
2-phenylethyl acetate increased 3- to 10-fold, 3.8- to 12-fold, and 2- to 10-fold, respectively, depending on the fermentation temperature,
cultivar, and yeast strain used. The concentrations of ethyl caprate,
ethyl caprylate, and hexyl acetate only showed minor changes, whereas the acetic acid concentration decreased by more than half. These changes in the wine and distillate composition had a pronounced effect
on the solvent or chemical aroma (associated with ethyl acetate and
iso-amyl acetate) and the herbaceous and heads-associated aromas of the
final distillate and the solvent or chemical and fruity or flowery
characters of the Chenin blanc wines. This study establishes the
concept that the overexpression of acetyltransferase genes such as
ATF1 could profoundly affect the flavor profiles of wines
and distillates deficient in aroma, thereby paving the way for the
production of products maintaining a fruitier character for longer
periods after bottling.
0099-2240/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Effect of Increased Yeast Alcohol Acetyltransferase
Activity on Flavor Profiles of Wine and Distillates
*
Corresponding author. Mailing address: Institute for
Wine Biotechnology, University of Stellenbosch, Stellenbosch
7600, South Africa. Phone: (27) 21-8084730. Fax: (27) 21-8083771. E-mail: isp{at}maties.sun.ac.za.
Applied and Environmental Microbiology, February 2000, p. 744-753, Vol. 66, No. 2
0099-2240/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
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