The cloning and transformation of brandy yeasts with the alcohol acetyl transferase gene for improved ester formation
Bauer, F F
University of Stellenbosch. Faculty of AgriSciences. Institute for Wine Biotechnology
Lambrechts, M G
Gey van Pittius, M H
- 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.
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