Malolactic activity

Vidal et al. (2001) examined the inhibitory effect of two commonly used pesticides, copper and dichlofluanid, on several strains of O. oeni and on MLF in simulated wine. Sensitivity to these pesticides varied and was enhanced by the presence of ethanol. Inhibition was due to a decrease in cell number and not to a decrease in malolactic activity. Quinoxyfen,... 

Rosi 1., Fia, G., Canuti, V. (2003). Influence of different pH values and inoculation time on the growth and malolactic activity of a strain of Oenococcus oeni. Aust. J. Grape Wine Res., 9, 194-199. 

Vivas, N., Lonvaud-Funel, A., Glories, Y. (1997). Effect of phenolic acids and anthocyanins on growth, viability and malolactic activity of a lactic acid bacterium. Food Microbiol, 14, 291-300. 

Edwards and Beelman (1987) have reported decanoic acid to be inhibitory to the growth of malolactic bacteria. Edwards and Beelman (1987) noted that decanoic acid suppressed the growth of O. oeni PSU-1 at a concentration of 10 mg/L, a concentration reported to be present in some wines (Houtman et al., 1986). In addition, Carrete et al. (2002) reported that decanoic acid acted synergistically with either low pH level or ethanol to inhibit O. oeni ATPase, the activity of which has been linked to malolactic activity in O. oeni (Cox and Henick-Kling, 1995 Tourdot-Marechal et al., 1999). However, Edwards et al. (1990) found that MLF occurred more rapidly in wines containing 5 mg/L decanoic acid and other medium-chain fatty acids than in wines with lower levels. 

Capucho, I. and San Ramao, M.V. 1994. Effect of ethanol and fatty acids on malolactic activity of Leuconostoc oenos. Appl. Microbiol. Biotechnol. 42, 391-395. 

Tourdot-Marechal, R., Fortier, L.-P., Guzzo, J., Lee, B., and Divies 1999. Acid sensitivity of neomycin-resistant mutants of Oenococcus oeni A relationship between reduction of ATPase activity and lack of malolactic activity. FEMS Microbiol. Lett. 178, 319-326. 

Besides growth, the pH affects the malolactic activity of the entire cell. Although the optimum pH of the purified enzyme is 5.9, it is not the same for cells. The malolactic activity of 0. oeni strains is optimum at a pH between 3.0 and 3.2 and around 60% of its maximum activity at pH 3.8. The usual pH range of wines, therefore, corresponds well with the maximum malolactic activity of the bacterial cell. Yet the malolactic fermentation rate depends on not only the activity but also the quantity of cells. Finally, at usual wine values, the pH affects both in the same way. Consequently, when all other conditions are equal, malolactic fermentation is quicker at higher pHs. For example, malolactic fermentation lasts 164 days for a wine adjusted to pH 3.15 and 14 days for a wine adjusted to 3.83 (Bousbouras and Kunkee, 1971). 

The pH is therefore very important and comes into play at several levels in the selection of the best adapted strains in the growth rate and yield in the malolactic activity and even in the nature of the substrates transformed. 

Despite efforts to establish the necessary conditions, a Oenococcus oeni biomass inoculated in wine is not capable of degrading all of the malic acid present. The complete reaction can only be obtained by massive inoculations (1-5 g/1), which are not feasible in practice. In general, when the population has completely disappeared, the reaction stops, leaving maUc acid. In addition, the malolactic activity of conunercial preparations rapidly diminishes during conservation, even at low temperatures. 

Of all the metabolic activities that lactic acid bacteria can carry out in wine, the most important, or desirable, in winemaking is the breakdown of malic acid, but only when it is intended for this to be removed completely from the wine by malolactic fermentation. Although the breakdown of malic and citric acids has considerable consequences from a winemaking perspective, it is also evident that lactic acid bacteria metabolise other wine substrates to ensure their multiplication, including sugars, tartaric acid, glycerine and also some amino acids. We will now describe some of the metabolic transformations that have received most attention in the literature, or which have important repercussions in winemaking. 

This is the main reaction of MLR Chemically it consists of a simple decarboxylation of the L-malic acid in wine into L-lactic acid. Biochemically, it is the result of activity of the malolactic enzyme, characteristic of lactic acid bacteria. This transformation has a dual effect. On the one hand, it deacidifies the wine, in other words, it raises the pH, an effect that is greater at higher initial quantities of malic acid. It also gives the wine a smoother taste, replacing the acidic and astringent flavour of the malic acid, by the smoother flavour of the lactic acid. 

Comitini, F., Ferretti, R., Clementi, F., Mannazzu, 1., Ciani, M. (2005). Interactions between Saccharomyces cerevisiae and malolactic bacteria preliminary characterization of a yeast proteinaceous compound(s) active against Oenococcus oeni.J. Appl. Microbiol., 99, 105-111. 

Boido, E., Lloret, A., Medina, K., Carrau, E., DeUacassa, E. (2002). Effect of ss-gfycosidase activity of Oenococcus oeni on the glycosylated flavor precursors of Tannat wine during malolactic fermentation J. Agric. Food Chem., 50, 2344—2349. 

Cantos et al. 2003 Gambuti et al. 2004). It is also influenced by yeast enzymatic activities, in particular those of isomerase and glucosidase (Jeandet et al. 1994). Equally, activities of lactic acid bacteria, which are responsible for malolactic fermentation (Hernandez et al. 2007), can also affect stilbene content in wine (Poussier et al. 2003). Aging of wine appears to have no important influence on the concentration of stilbenes (Jeandet et al. 1995). 

In grapes or grape juices, the tartaric esters may be hydrolysed by enzymes from contaminant fungi or from commercial pectolytic preparations, both with cin-namoyl decarboxilase activity, releasing free hydroxycinnamic acid forms (Dugelay et al. 1993 Gerbaux et al. 2002). However, the tartaric esters are mostly hydrolysed after malolactic fermentation (Hernandez et al. 2006, 2007), it being hypothesised that the hydrolytic activity of lactic acid bacteria follows the completion of malic conversion to lactic acid (Cabrita et al. 2007) (see Table 11.4). 

There is no available method to remove this taint effectively (Lay 2004). The removal of precursors (L-lysine and ethanol) is not feasible. As it depends on microbial activity, the preventive measures are similar to those suggested for volatile phenols when there is the risk of D. bruxellensis infection. The prevention of spoilage by heterofermentative lactic bacteria usually advised, like decreasing wine pH values and rapid inactivation by sulphur dioxide, once malolactic conversion is finished, should also be effective against bacterial mousiness. 

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