Lactic acid in wine

In discussing the studies of Brechot et al. (24) and Peynaud et al. (25), Kunkee (I) found it odd that bacteria which ordinarily produce d or DL-lactic acid from glucose produce L-lactic acid in wine as a result of malo-lactic fermentation. Peynaud et al. (26) reported that organisms which produced only D-lactic acid from glucose produced only L-lactic acid from L-malic acid. He postulated further that the malo-lactic fermentation pathway has no free pyruvic acid as an intermediate because the optical nature of L-malic acid would be lost when it was converted to pyruvic acid since pyruvic acid has no asymmetric carbon atom. Therefore, if pyruvic acid were the intermediate, one would expect d, l, or DL-lactic acid as the end product whereas L-lactic acid is always obtained. These results lend considerable support to the hypothesis that free pyruvic... 

Decarboxylation 21 Malic acid to lactic acid (in wines) amino acids to amines (histamine and tyramine accumulate in soft cheeses because of surface growth of lorulopsis Candida and Debaryomvces kloeckera). 

Determination of L-Malic and L-Lactic Acids in Wines and Musts... 

E. Mataix, M.D. Luque de Castro, Determination of L-(-)-malic and L-(+)-lactic acid in wine by a flow injection-dialysis-enzymic derivatisation approach, Anal. Chim. Acta 428 (2001) 7. 

Ll. Buglass, A. J. and S. H. Lee. 2001. Sequential analysis of malic acid and both enantiomers of lactic acid in wine using a high-performance liquid chromatographic column-switching procedure./. Chromatogr. Sci. 39 453-458. 

Puchades, R., M. A. Herrero, A. Maquieira, and J. Atienza. 1991. Simultaneous enzymatic determination of L(—) malic acidand L(-i-) lactic acid in wine by flow injection analysis. Food Chem. 42 167-182. 

Leuconostocaceae are non-endospore-forming and facultatively anaerobic rods or cocci, usually characterized by the production of equimolar amounts of lactic acid, ethanol, and carbon dioxide from glucose (obligately heterofermentative metabolism, see below). Exceptions are members of the genus Fructobacillus, which produce acetic acid instead of ethanol (Endo and Okada 2008). Also, some species of the genus Leuconostoc possess heme-dependent respiratory capability. Genus Oenococcus, in particular species O. oeni, is considered important thanks to the ability to convert L-malic acid to L-lactic acid in wine (Henick-Kling 1993). 

The sugars in fruits such as grapes are feimented by yeasts to produce wines. In winemaking, lactic acid bacteria convert malic acid into lactic acid in malolactic fermentation in fruits with high acidity. Acetobacter and Gluconobacter oxidise ethanol in wine to acetic acid (vinegar). 

Total Acid. Simple titration procedures are used to determine total acidity. Problems arise because of the widely varying amounts of different acids in wines tartaric, malic, citric, lactic, succinic, acetic, etc. Different pKtt values for these acids make it impossible to predetermine easily the correct pH of the endpoint. Since a strong base is being used to titrate relatively weak acids, the endpoint will be greater than pH 7. In this country phenolphthalein (8.3) or cresol red (7.7) endpoints or a pH meter to 9.0 have been used (3, 6, 12, 76, 77) and the results are expressed as tartaric acid. The result at pH 7.7 X 1.05 approximately equals the result of titrating to pH 8.4. In Europe pH 7 is usually the endpoint, in France the results are expressed as sulfuric acid, and in Germany as tartaric or in milliequivalents (78). 

The possibility of determining the acids in wines from the titration curve using special equations has been extensively investigated in Portugal by Pato and coworkers (79). To keep the ionic force constant, appropriate dilution is needed. Tartaric, malic, lactic, and succinic acid were determined in musts and wines. 

Fumaric Aero Inhibition. Another means of preventing malo-lactic fermentation is to add fumaric acid after alcoholic fermentation is complete (45, 46, 47,48). The inhibition is relative and its extent is dependent on the amount added. The susceptibility to fumaric acid is also dependent on the strain of malo-lactic bacteria tested (49). However, we know of no case where fumaric acid addition at the levels suggested by Cofran and Meyer (45) (about 0.05%) did not delay malo-lactic fermentation under normal winemaking conditions. This includes several experiments from our pilot winery (50). Nevertheless, we have not been hasty to recommend the use of fumaric acid as an inhibitor because 1) of the difficulty in solubilizing the acid in wine 2) we do not know the mechanism of action of its inhibition [Pilone (47, 48) has shown that the bacteria metabolize low levels of fumaric acid to lactic acid but, at inhibitory levels at wine pH, the acid is bactericidal] and 3) of the desirability of minimizing the use of chemical additives. 

Tyj"alo—lactic fermentation can be defined as the bacterial conversion of L-malic acid to L-lactic acid and carbon dioxide during storage of new wine. Malic acid is dicarboxylic, but lactic acid is monocarboxylic therefore, the net result of malo-lactic fermentation in wine, aside from the production of carbon dioxide, is a loss in total acidity. In commercial practice, this fermentation is not well understood, and better methods of controlling it are sought. 

The growth of malo-lactic bacteria in wines is favored by moderate temperatures, low acidity, very low levels of S02, and the presence of small amounts of sugar undergoing fermentation by yeast. It is frequently possible to inoculate a wine with a pure culture of a desirable strain of bacteria and obtain the malo-lactic fermentation under controlled conditions. The pure-culture multiplication of the selected strain of bacteria is difficult, however. It is also difficult to control the time of the malo-lactic fermentation—sometimes it occurs when not wanted, and at other times will not go when very much desired. For the home winemaker it is probably most satisfactory to accept the malo-lactic fermentation if it occurs immediately following the alcoholic fermentation. The wines should then be siphoned away from deposits, stored in completely filled containers at cool temperatures, and have added to them about 50 ppm S02. If the malo-lactic fermentation does not take place spontaneously and the wine is reasonably tart, the above described regime of preservation will likely prevent its occurrence. When the malo-lactic transformation takes place in wines in bottles, the results are nearly always bad. The wine becomes slightly carbonated, and the spoiled sauerkraut flavors are emphasized. 

M. Albareda-Sirvent and A.L. Hart, Prebminary estimates of lactic and malic acid in wine using electrodes printed from inks containing sol-gel precursors, Sens. Actuators B Chem., 87(1) (2002) 73-81. 

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. 

Many LAB found in wines can improve wine quality by metabolizing malic acid to lactic acid in a process called malolactic fermentation (MLF). This fermentation is an enzyme-mediated decarboxylation of the dicarbox-ylic acid, L (—) malic acid, to the monocarboxylic L (+) lactic acid (Amerine et al., 1980 Kunkee, 1967 Lonvaud-Funel, 1999). MLF decreases wine acidity and is particularly important in wines produced from grapes grown in cool climates, which often have high acidity (Beelman and Gallander, 1979 Kunkee, 1967, 1974). 

Liithi, H. and Vetsch, U. 1959. Contributions to the knowledge of the malo-lactic fermentation in wines and ciders. II. The growth promoting effect of yeast extract on lactic acid bacteria causing malo-lactic fermentation in wines. J. Appl. Bacteriol. 22, 384-391. 

Organic acid content in wine has an important impact on organoleptic characteristics of the wine. a-Hydroxy acids (tartaric, malic, lactic, and citric acids) are mainly responsible for these characteristics. Other acids in wines include acetic, ascorbic, gluconic, and sorbic acids, as well as sulfite, sulphate, phosphate, and malonate (Masar et al., 2001). 

Excessive amounts of acetic acid in wine are due to the action of anaerobic lactic bacteria or aerobic acetic bacteria. Together with other molecules, this acid plays a major part in organoleptic defects of bacterial origin. On the other hand, myco-dermic (Section 8.3.4) and Brettanomyces yeasts (Section 8.4.6) cause defects that do not involve accumulations of this acid. 

Colorimetric methods are used for the determination of lactic and tartaric acids in wines. In the determination of lactic acid the procedure consists of the conversion of lactic acid into acetaldehyde by heating in the presence of sulfuric acid or by oxidation with cerium(IV) sulfate and subsequent formation of a colored compound with p-hydroxydiphenyl or piperidine and sodium nitroprusside. The red color formed is measured at 560-570nm. 

The acids present in a given wine are determined by the grape variety, climate, presence of gray rot [Botrytis cinerea), yeasts, bacteria, and various treatments to which the wine may be subjected (sulfur dioxide, ascorbic acid, acidification, desacidifica-tion). There are at least 50 different acids in wine ranging in concentration from 1 or 2gl (tartaric, malic, succinic acids) to hundreds of mgl (citric, lactic, acetic acids) to tens of mgl (pyruvic, shikimic acids). However, tartaric, malic (depending on the MLF), acetic, and succinic acids constitute 80-90% of total complement of wine acids. 

Tyman (1996) provided a good discussion of applications of TLC to the analysis of carboxylic acids used as preservatives or as medicinal agents. Of particular interest is mention of the use of TLC for the simultaneous detection of benzoic, citric, and lactic acids in soft drinks, benzoic acid in textile fibers and food preparations, and hydroxybenzoic acid in wines. A variety of techniques and layers (including polyamide and silanized silica gel) have been used in these separations. 

OuGH, C.S. and R.E. Kunkee. 1974. The effect of fumaric acid on malo-lactic fermentation in wine from warm areas. Am.J. Enol. Vitic. 25 188-190. 

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