Eveline Bartowsky,* Hugo Campbell, Roman Mink, Alexia Klein, Patrick Lucas, Maren Scharfenberger-Schmeer, Magali Déléris, and Sibylle Krieger-Weber
*Lallemand Australia, 23-25 Erudina Avenue, Edwardstown, Adelaide SA, Australia (ebartowsky@lallemand.com)

Diacetyl is a major flavor metabolite produced by wine-associated lactic acid bacteria (LAB). In wine, diacetyl has important stylistic implications. Depending on the style and type of wine, it is considered to contribute a desirable ‘buttery’ or ‘butterscotch’ flavor character. For a fruit-driven white wine, diacetyl production should be minimized, because it will mask the varietal aroma. Formation of diacetyl is closely linked to the growth of wine LAB such as Oenococcus oeni and the metabolism of sugar, malic acid and citric acid. As part of the selection and commercialization process, potential starter strains are studied for their citric acid metabolism and diacetyl formation. A study undertaken by Bartowsky et al. (2010) in Cabernet Sauvignon wines demonstrated that different O. oeni strains will produce significantly different concentrations of diacetyl when used in sequential MLF inoculation. Recently, Mink et al. demonstrated that pyruvate is a central metabolite in diacetyl synthesis by O. oeni. Diacetyl formation by O. oeni is induced by yeast-derived pyruvate in the early stage of winemaking, resulting in diacetyl accumulation in the wine. We have analyzed and reassembled 296 O. oeni genome sequences, including those publicly available and from the University of Bordeaux. The citrate operon of a group of O. oeni strains and citric acid metabolism was examined to identify potential genetic markers that could predict the consumption of citrate during MLF. Besides choosing the appropriate strain, application of certain winemaking practices will also help modulate diacetyl content in wine through malolactic fermentation.

Funding Support: Lallemand; State Education and Research Center of Viticulture and Horticulture, Neustadt, Germany; European project – Marie Currie funding