Abstract
Pyruvate is the central metabolite in diacetyl synthesis by <i>Oenococcus oeni.</i> Therefore, any substrate that increases intracellular pyruvate concentration can induce diacetyl accumulation. This study evaluates the effect of exogenous pyruvate on diacetyl formation and the expression of diacetyl-related genes in <i>Oenococcus oeni</i> during winemaking. Diacetyl formation by <i>Oenococcus oeni</i> was induced by yeast-derived pyruvate in the early stage of winemaking. Furthermore, when additional pyruvate was added, α-acetolactate synthase (<i>alsS</i>) gene expression increased 1.6-fold and the diacetyl concentration increased from 0.4 mg/L to 2.3 mg/L. Although the highest <i>alsS</i> expression (a 10-fold increase) was found 24 hr after pyruvate addition, no further increase in diacetyl concentration was found. In addition, <i>alsD</i> was overexpressed (9-fold) at that point, indicating that α-acetolactate was converted into acetoin. Together, the results show that exogenous pyruvate induces diacetyl formation by <i>Oenococcus oeni</i> in the early stage of winemaking<i>.</i> Furthermore, pyruvate-derived diacetyl accumulates because of a delayed <i>alsD</i> response that prevents acetoin formation.
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