Influence of succinic acid on Oenococcus oeni and malolactic fermentation

As a consequence of the alcoholic fermentation carried out by yeasts in wine, several compounds can be delivered to the medium, promoting or inhibiting the malolactic fermentation (MLF) and the lactic acid bacteria, mainly Oenococcus oeni. Succinic acid is one of these compounds and is an example of the interaction between yeasts, including non-Saccharomyces species, and O. oeni. However, the influence of succinic acid on the MLF has been researched very little as yet. In this work, we study the influence of succinic acid and pH on O. oeni CH11 and PSU-1 strains, both during MLF and in resting cell experiments. Moreover, we analysed the relative expression of some significant genes related to stress and malolactic activity to determine how the O. oeni strains were affected by the succinic acid. The results showed that the succinic acid could act as an MLF inhibitor at concentrations higher than 1 g/L, but it can be beneficial at 0.5 g/L. This variable effect also depends on the strains and other winemaking conditions, mainly pH, which influences the dissociated and undissociated forms of both acids. The inhibiting effect of succinic seems clearer when it is at a molar concentration higher than that of L-malic acid. Experiments with resting cells have confirmed that O. oeni consumes less L-malic acid when succinic acid is higher than 1 g/L. Genetic expression experiments showed that in the presence of succinic acid (2 g/L), gene hsp18 encoding stress protein was up-regulated in strain CH11, suggesting a good response and adaptation of this strain to stress. On the other hand, genes mleA and mleP, which are related to malolactic activity, were not affected by succinic acid, except for strain PSU-1 at pH 4.0. Further research is necessary to understand better the effects of succinic acid on O. oeni and MLF.