Fermentation, malolactic acidity during

A.2.2 Evolution of Free Amino Acids During Malolactic Fermentation. 166... 

Soufleros et al. (1998) noted that biogenic amines are formed from their precursor amino acid during and after spontaneous malolactic fermentation. Spoilage bacteria such as Pediococcus 3.nd Lactobacillus hud been implicated (Delfini, 1989 Moreno-Arribas et al., 2000 2003 Arena and Manca de Nadra, 2001), however, yeast strain used for alcoholic... 

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. 

Patynowski et al. (2002) showed that yeasts produce an unidentified inhibitory factor (maybe a toxic metabolite) that could be responsible for the inhibition of bacterial growth. These results could explain the antagonism between yeasts and malolactic bacteria, since yeasts are known to produce compounds during alcoholic fermentation such as ethanol, SO2, medium-chain fatty acids and antibacterial proteins/peptides (Weeks et al. 1969 De Oliva et al. 2004 Comitini et al. 2005 Osborne and Edwards 2007). The nature and quantity of peptides and other molecules released by yeasts are different depending on winemaking techniques and the yeast strain. 

As well as fruity and buttery aromas, MLF has also been associated with other characteristic aromas such as floral, roasted, vanilla, sweet, woody, smoked, bitter, honey, etc. (Flenick-Kling 1993 Sauvageot and Vivier 1997). However, further studies are required to be able to relate the wine characteristics that are modified during malolactic fermentation with the production and/or degradation of a specific chemical compound by wine lactic acid bacteria. With this information, the winemaker can choose the best strain of lactic acid bacteria to obtain wine with a specific aroma or flavour. 

Malolactic fermentation usually occurs in sobretablas wine as a result, the wine incorporated into the aging system contains no appreciable concentrations of malic acid. The decrease in tartaric acid contents during biological aging of the wine is a result of crystal precipitations. 

Davis, C.R., Wibowo, D.J., Lee, T.H. Eleet, G.H. (1986). Growth and metabolism of lactic acid bacteria during and after malolactic fermentation of wines at different pH. Appl. Environ. Microbiol, 51, 539-545. 

The interaction between aroma compounds and other wine micro-organisms (e.g. lactic acid bacteria) or with metabolites produced during malolactic fermentation has been studied to a limited extent. Interactions between polysaccharides produced by the most common wine lactic bacteria (Oenoccocus oeni) during malolactic fermentation have been shown to be responsible for the reduced volatility of some aroma compounds in wines (Boido et al. 2002). The possibility of direct interactions between the surface of the bacteria cells and aroma compounds should also be considered since this type of interaction has been found for other food lactic bacteria (Ly et al. 2008). 

In addition to S02 and antibacterial proteins/peptides, medium-chain fatty acids produced by yeast during alcoholic fermentation have also been implicated in the inhibition of malolactic bacteria (Carrete et al, 2002 Edwards and Beelman, 1987 Lonvaud-Funel et al, 1985). Inhibition of Saccharomyces species and some LAB by medium-chain fatty acids has been reported in grape juice and silage (Pederson et al, 1961 Woolford, 1975). Although this hypothesis has not been conclusively shown, Lonvaud-Funel et al (1985) and... 

Another advantage of partial elimination of malic acid followed by the addition of tartrate over malolactic fermentation is that, due to the low acidification rate, it does not produce wines with too low a pH, which can be responsible for difficult or stuck second fermentation in the bottle during the champagne process, leaving residual sugar in the wine. 

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