Weak malolactic fermentations in wine making are often attributed to the medium constituents such as ethanol and SO2. However, some authors report that the interactions between Saccharomyces cerevisiae and Leuconostoc oenos could be responsible too.
The aim of this work is to characterize the influence of S. cerevisiae on the growth of L. oenos. First, a qualitative study was performed on solid medium containing 8 g/l of L-malic acid. In this case, L. oenas was mixed to M.R.S agar and poured into Petri plate, then S. cerevisiae was seeded in rings on the agar surface. After incubation, the coculture result in an inhibition of L. oenos growth by S. cerevisiae.
In order to quantify this phenomenon, a culture of L. oenas was carried out on liquid medium prefermented by S. cerevisiae (supplied with M.R.S nutrients) and was compared with a control on M.R.S medium. Both contained 8 g/l of L-malic acid. This technique allows to separate the microorganisms in order to avoid competitions between the strains.
The prefermented medium affects L. oenos growth and the malolactic fermentation, but the results depended on the pH and the temperature. Globally, low pH (3,4) and high temperature (30°C) conditions increased the inhibitory effect of the prefermented medium. This medium contains inhibitory molecules for L. oenas. In agreement with some authors, those molecules could be the medium chain fatty acids (C8 to C12) released in the medium by S. cerevisiae because of their pH-dependent toxicity. However, those results may be different with other couples of strains of S. cerevisiae and L. oenos.
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