Understanding Citric Acid and Ester Metabolism - Producing Fruitier Wines

Project Number
IWBT-B 11-02

Project title
Understanding citric acid and ester metabolism – producing fruitier wines

Project leader
Du Toit, M A

Stellenbosch University. Department of Viticulture and Oenology

Team members
Du Toit, M A
Divol, B
Engelbrecht, L

Project description
Lactic acid bacteria have the potential to impact wine aroma and flavour compounds through the production of secondary metabolites. Two of the metabolic pathways that have an indirect or direct impact on fruity characteristics of wine are citric acid metabolism and the production of esters. In a previous project, we have identified lactic acid bacteria strains that have different combinations of enzyme-encoding genes related to these two metabolic pathways. Since the production of diacetyl can negatively impact on the perception of fruitiness in wine, it is important to understand the functioning of these enzymes and how we can reduce the production of diacetyl. Moreover, it is not clear whether and/or in which conditions extracellular esterases produce or hydrolyse esters.

The ultimate aim is to generate knowledge on the functioning of the genes and corresponding enzymes of the citric acid metabolic pathway and the production or hydrolysis of esters under various winemaking conditions. Understanding the regulation of the genes involved in the citric acid metabolic pathway and the factors that influence the functioning of the enzymes will allow us to manipulate the production of diacetyl and therefore enhance the fruity character of wine. This is especially relevant in the production of Chardonnay where malolactic fermentation is needed to enhance fruitiness but high levels of buttery character are not always wanted. If more esters can be produced by the esterase activity of lactic acid bacteria during malolactic fermentation, this can enhance the fruitiness of white and red wine.


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