Malolactic fermentation

The malolactic fermentation occurs in many heterofermentative lactic acid bacteria and yeasts, and plays a role in wine, fruit juice and champagne production. It is also known as malolactic fermentation or malic acid -lactic acid fermentation. The malolactic fermentation is a secondary fermentation, which as a result has the breakdown of acid in the medium. It follows a primary alcohol -producing fermentation. Wherein the malolactic fermentation certain lactic acid bacteria decarboxylate the dicarboxylic L-malate ( = deprotonated form of the L-malic acid ) to the energy weaker monocarboxylic L-lactate ( = deprotonated form of the L- lactic acid). In the yeast Saccharomyces cerevisiae, the lactic acid is further degraded and fermented into ethanol.

The resulting by this fermentation malolactic fermentation leads to the production of wine in a harmonious and balanced flavor profile - an effect which increase quality impacts, but also are the risks: Acid arms wines are less durable, less " bubbly " and do not seem so fresh.

Occurrence

The malolactic fermentation takes place in many microorganisms that operate to produce energy, a heterofermentative fermentation. For the production of wine Oenococcus oeni ( Leuconostoc oenos old name ) is important, furthermore Lactobacillus spp. (e.g., Lactobacillus plantarum ), and Pediococcus spp.

Yeasts such as S. cerevisiae can operate malolactic fermentation at the end of alcoholic fermentation.

Biochemistry

Process

In the malolactic fermentation, the decarboxylation of L- malate is catalyzed to L- lactate. Depending on the pH value of the medium or malate lactate may also be protonated

In this reaction, the total amount of acid in the wine is reduced by 0.4 g/LH2SO4 with each gram of malic acid degraded.

S. cerevisiae malate builds from an NADH -dependent malic enzyme to lactate. This NADH is produced. Lactate finally decarboxylated to acetaldehyde, which is then reduced to ethanol. The reduction requires NADH. Therefore, one can strictly speaking only when Malatabbau in yeast from a fermentation, while decarboxylation bacteria.

Energy

Under standard conditions, energy is released in the decarboxylation reaction. This value is dependent on the pH value. At pH 7 to 26.5 kJ mol-1, at a pH value of 5.7 33.9 kJ mol-1 to be released. In wines, the pH may well be at 3.5, then be free under standard conditions 46.5 kJ · mol -1. However, it is to be noted that not exist under physiological conditions malate, lactate and CO2 at a concentration of 1 mol · L -1, and during the process of continuously consumed malate and lactate is produced. Therefore, the energy gain is low under physiological conditions.

The energy released in the decarboxylation energy is conserved in the form of a chemiosmotic mechanism ( see illustration). In O. oeni, which grows at a pH of about 4, easy ( MleP ) is protonated malate ( HMal1 ) by a membrane-bound carrier brought into the cell. This is decarboxylated to lactate, which is present at pH 4 protonated ( HLAC ). The effluent from the cell at the HLAC done without a carrier. Lactococcus lactis grows at higher pH values ​​and malate ( MAL2 ) is replaced with lactate ( LAC 1 ) by an antiporter ( MleP ).

In both cases a (negative ) charge is transported in the net, resulting in energization of the membrane. In addition, during the decarboxylation, consumes a proton, so that a proton concentration difference can be established. Thus, both processes lead to a build up of an electrochemical gradient ( proton motive force). It is used by the bacteria in order to maintain the pH and absorption of nutrients. However, the liberated during the malolactic fermentation, energy is not sufficient as the only source of energy, so that the heterofermentative lactic acid bacteria are still dependent on the fermentation of pentoses and hexoses, respectively.

History

End of the 19th century has been furnished by Alfred Koch evidence that bacteria are responsible for the reduction in acid wines. These findings were published in 1900 during a meeting of the German Viticulture Congress in Colmar. More Erkennisse, such as the negative effects of acid bacterial degradation preconceived 1913 Hermann Müller ( Thurgau ) and Adolf Osterwalder in a publication together.

Although the chemical reaction was known by the work of Wenzel Seifert at the Federal College and Federal Office for Viticulture and Pomology at Klosterneuburg since the early 1920 years, yet it took almost 40 years to a deeper understanding of the malolactic fermentation.

May be that the Malatabbau also caused by yeasts, was proposed by Paul Julius Kulish and Wortmann. J. Zhukov provided for this purpose in the Geisenheim Research the proof. However, until many years later that fact paid attention to and taken up by the work of Radle in the 1990s again.

6425
de