Diacetyl Formation by Oenococcus oeni during Winemaking Induced by Exogenous Pyruvate

Abstract

Pyruvate is the central metabolite in diacetyl synthesis by Oenococcus oeni. 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 Oenococcus oeni during winemaking. Diacetyl formation by Oenococcus oeni was induced by yeast-derived pyruvate in the early stage of winemaking. Furthermore, when additional pyruvate was added, α-acetolactate synthase (alsS) gene expression increased 1.6-fold and the diacetyl concentration increased from 0.4 mg/L to 2.3 mg/L. Although the highest alsS expression (a 10-fold increase) was found 24 hr after pyruvate addition, no further increase in diacetyl concentration was found. In addition, alsD 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 Oenococcus oeni in the early stage of winemaking. Furthermore, pyruvate-derived diacetyl accumulates because of a delayed alsD response that prevents acetoin formation.