Abstract
Oenococcus oeni is the main agent of malolactic fermentation in wine. This fermentation takes place after alcoholic fermentation, in a low nutrient medium where ethanol and other inhibitor compounds are present. In addition, some yeast-derived compounds such as mannoproteins can be stimulatory for O. oeni. The mannoprotein concentration in wine depends on the fermenting yeasts, and non-Saccharomyces in particular can increase it. As a result of the hydrolytic activity of O. oeni, these macromolecules can be degraded, and the released mannose can be taken up and used as an energy source by the bacterium. Here we look at mannoprotein consumption and the expression of four O. oeni genes related to mannose uptake (manA, manB, ptsI, and ptsH) in a wine-like medium supplemented with mannoproteins and in natural wines fermented with different yeasts. We observe a general gene upregulation in response to wine-like conditions and different consumption patterns in the studied media. O. oeni was able to consume mannoproteins in all the wines. This consumption was notably higher in natural wines, especially in T. delbrueckii and S. cerevisiae 3D wines, which presented the highest mannoprotein levels. Regardless of the general upregulation, it seems that mannoprotein degradation is more closely related to the fermenting medium.
Highlights
We look at mannoprotein consumption and the expression of four O. oeni genes related to mannose uptake in a wine-like medium supplemented with mannoproteins and in natural wines fermented with different yeasts
Malolactic fermentation (MLF) is a biotransformation undergone in fermented beverages with low nutrient composition by different lactic acid bacteria (LAB) [1,2,3]
The aim of this paper is to evaluate the ability of O. oeni to utilize yeast mannoproteins in different fermentation media and to study the transcriptional response of mannose-related genes as possible indicators of mannose consumption
Summary
Malolactic fermentation (MLF) is a biotransformation undergone in fermented beverages with low nutrient composition by different lactic acid bacteria (LAB) [1,2,3] It is usually performed in wine and cider and results in an increase in pH values because of the decarboxylation of L-malic acid into L-lactic acid, an improvement of organoleptic wine characteristics and an increased microbiological stability [4,5,6]. As a result of the transformation of grape must into wine (or apple juice into cider), the media in which the LAB ferments will have low concentrations of nutrients, high acidity, and high concentrations of ethanol and sulphur dioxide All these changes select the LAB most suited to this stressful environment, of which Oenococcus oeni is the best adapted species [1,11,12].
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