Time course of diacetyl formation during vinification with Saccharomyces cerevisiae and Oenococcus oeni co-cultivation

摘要

Background and Aims: Diacetyl accumulation in wine, which has undergone malolactic fermentation by Oenococcus oeni, is often associated with aromatic off-flavours. Characterisation of the diacetyl-related metabolic pathway helps to explain bacterial diacetyl formation during winemaking. The present study describes the time-dependent formation of diacetyl during the vinification process after simultaneous, induced malolactic fermentation by freeze-dried O. oeni on the basis of gene-expression analysis of the citrate- and pyruvate-derived pathways. Methods and Results: After simultaneously induced malolactic fermentation in Pinot Blanc by O. oeni, the dynamics of diacetyl formation were compared with citrate consumption and gene-expression of the diacetyl-related metabolic pathways. Diacetyl concentration showed two maxima: the first increase was primarily influenced by the activity of Saccharomyces cerevisiae; however, the second increase was induced only by O. oeni and correlates with bacterial citrate degradation. Expression of the alsS gene showed two significant responses; however, only the second response was affected by the citrate-associated genes maeP and citE. Additionally, alsD and butA2 were found to be continuously underexpressed during the winemaking process. Conclusions: Taken together, we suggest that diacetyl accumulation during the vinification process by O. oeni is affected by citrate fermentation. The diacetyl-related alsS gene, however, is also overexpressed independently by other substrates, which may also increase the intracellular pyruvate level resulting in diacetyl formation. Significance of the Study: Characterisation of the time-dependent diacetyl accumulation and its degradation during the vinification process is essential for the development of strategies that focus on the suppression of the diacetyl concentration below the sensory threshold.