The cloning and transformation of brandy yeasts with the alcohol acetyl transferase gene for improved ester formation


Project Number
IWBT 02-02

Project title
The cloning and transformation of brandy yeasts with the alcohol acetyl transferase gene for improved ester formation

Project leader
Bauer, F F

Institution
University of Stellenbosch. Faculty of AgriSciences. Institute for Wine Biotechnology

Team members
Lambrechts, M G
Lilly, M
Gey van Pittius, M H

Project description
– To overexpress the alcohol acetyl transferase (ATF1) gene in a rebate wine yeast.
– To determine the amount of esters formed during fermentation.
– To determine how this higher concentration of esters influences the aroma profile of brandy.
– To determine whether the overexpression of ATF1 has significant side effects on the yeast cell’s metabolism.
– To use this knowledge to clone other genes involved in longer chain ester formation.

Esters, which impart fruity aromas to wine, are important contributors to the fermentation bouquet. Evidence indicates that the special fruity odour is primarily due to a mixture of hexyl acetate, ethyl caproate and isoamyl acetate. Acetate esters, such as isoamyl acetate (banana-like aroma) and ethyl acetate (light-fruity, solvent-like aroma) are recognised as important flavour compounds in several alcoholic beverages. In fact, isoamyl acetate is important for the unique character of Pinotage wines. Esters are also important products in the distillate of rebate wine and therefore contribute to the character of brandy. The ATF1 gene, from Saccharomyces cerevisiae, encodes the enzyme alcohol acetyltransferase (Atf1p) that has been shown to be involved in the formation of isoamyl- and ethyl acetate. Alcohol acetyl transferase, which is located in the vacuole, forms these esters from acetyl-CoA and alcohols. It has recently been shown that apart from the Atf1p, Saccharomyces cerevisiae contains at least one other isoamyl alcohol acetyl transferase and ethanol acetyltransferase enzyme. The genes encoding these two enzymes have not yet been cloned. The ATF1 gene is strongly repressed under aerobic conditions or by the addition of unsaturated fatty acids to a culture and thus the Atf1p production is decreased.

Presentation(s)
De Villiers, M, Lambrechts, M G and Pretorius, I S. 1997. Manipulating ester production by recombinant wine yeast. Paper presented at the 22nd National Congress of the South African Society for Enology and Viticulture. 13-15 November, Cape Town, South Africa

De Villiers, M, Lambrechts, M G and Pretorius, I S. 1998. Manipulating ester production by recombinant wine yeast. Paper presented at the 2nd International Congress of the Federation of African Societies of Biochemistry and Molecular Biology. Potchefstroom, South Africa.

Lambrechts, M G, Lilly, M and Pretorius, I S. 1999. The effect of yeast alcohol acetyltransferase activity on the sensorial quality of wine and brandy. Paper presented at the 19th International Conference on Yeast Genetics and Molecular Biology. 25-30 May, Rimini, Italy

Lambrechts, M G, Lilly, M and Pretorius, I S. 1999. The effect of yeast alcohol acetyltransferase activity on the sensorial quality of wine and brandy. Paper presented at the 24th International Wine Congress. Mainz, Germany.

Lambrechts, M G, Lilly, M and Pretorius, I S. 1999. The effect of yeast alcohol acetyltransferase activity on the sensorial quality of wine and brandy. Paper presented at the 6th International Enology Symposium. 10-12 June, Bordeaux, France.

Article
Lilly, M, Lambrechts, M G, Pretorius, I S. 2000. Effect of increased yeast alcohol acetyltransferase activity on flavor profiles of wine and distillates, Applied and Environmental Microbiology, Mnth Feb v. 66 (2) (p. 744-753)
http://aem.asm.org/content/66/2/744.full

FinalReport.pdf

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