Malic acid bacterial transformation

Therefore, the hypothesis of the existence of an enzyme catalyzing the direct decarboxylation of L-malic acid into L-lactic acid was made. The enzyme, called the malolactic enzyme, was isolated for the first time in Lactobacillus plantarum (Lonvaud, 1975 Schiitz and Radler, 1974). From acellular bacterial extracts and thanks to successive purification stages, the authors obtained purified fractions responding to the fnnctional criteria of the malolactic enzyme. L-Malic acid is transformed stoichiometrically into L-lactic acid. These fractions do not have an LDH activity. 

This reaction therefore involves a decarboxylation without an intermediary product capable of following another metabolic pathway. Several authors have reported that certain bacterial strains form other molecules from malic acid, suggesting in this manner the existence of other reactions. Even if their existence cannot be ruled out, malolactic transformation is the only reaction that exists in the lactic acid bacteria involved in winemaking. 

The malolactic fermentation phase begins during the growth phase, as soon as the total population exceeds lO UFC/ml. It continues and is completed during the stationary phase, or sometimes at the beginning of the death phase. In very favorable conditions with a limited concentration of malic acid, malolactic fermentations are often completed even before the end of the growth phase. The optimum population in these cases exceeds 10 UFC/ml. As soon as a sufficient biomass is formed, malic acid is degraded. The malolactic acid bacterial activity is always present but depends on various conditions, especially the temperature. The transformation of 2 g of malic acid per liter can take more time than 4 g/1 if the population level attained is lower. 

The only bacterial intervention truly sought after in winemaking is the transformation of malic acid into lactic acid (Section 12.7.2). It is the source of the most manifest organoleptic change, resulting from malolactic fermentation the deacidification and the softening of wine. Malic acid, a dicarboxylic acid, is transformed molecule for molecule into lactic acid, monocarboxylic. The loss of an acid function per molecule is intensified by the replacement of an acid with... 

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