Fermentation malic acid

In warmer vintages in the North Coast, grapes, especially riper grapes at 23°-24° Brix, may be low in titratable acidity. Desirable levels of acidity in white juice prior to fermentation range from 0.7 to 1.0 g/100 mL, depending on final wine composition and wine style desired. Tartaric acid is used most commonly for acidulation and often is added to juice prior to fermentation. Malic acid and citric acid also are used for acidulation. 

At the end of alcoholic fermentation, malic acid concentrations should be determined and monitored if necessary. Malolactic fermentation (MLF) normally occurs after the complete depletion of sugars. An early initiation of MLF is generally linked to alcoholic fermentation difficulties and insufficient sulfiting. In certain cases, the two fermentations take place simultaneously, even though the antagonistic phenomena between yeasts and bacteria tend to inhibit alcoholic fermentation. 

Alcohol is the first limiting factor of malolactic fermentation. Malic acid concentrations often decrease fastest in tanks containing the lowest alcohol concentrations. Leuconostoc oenos (now known as Oenococcus oeni) is predominantly responsible for malolactic fermentation in red wines and it cannot grow in alcohol concentrations exceeding 14% volume. Some lactobacilli can resist 18-20% volume alcohol and are apt to cause spoilage in fortified wines. Besides alcohol production, the wine yeast strain responsible for alcoholic fermentation affects bacterial growth and malolactic fermentation. It yields macromolecules (polysaccharides and proteins) to the medium. The enzymatic systems of the bacterial cell wall hydrolyze these substances. 

In addition to alcohoHc fermentation, a malolactic fermentation by certain desirable strains of lactic acid bacteria needs to be considered. Occasionally, wild strains produce off-flavors. Malolactic fermentation is desirable in many red table wines for increased stabiUty, more complex flavor, and sometimes for decreased acidity. Selected strains are often added toward the end of alcohoHc fermentation. AH the malic acid present is converted into lactic acid, with the resultant decrease of acidity and Hberation of carbon dioxide. Obviously this has more effect on the acidity the more malic acid is present, and this is the case in wine from underripe, too-tart grapes. Once malolactic fermentation has occurred, it does not recur unless another susceptible wine is blended. 

Other Food Uses. Jellies, jams, and preserves use malic acid to balance flavor and adjust pH for pectin set. Canned fmits and vegetables employ malic acid in combination with ascorbic acid to produce a synergistic effect that aids in the reduction of browning. Wine and cider producers use malic acid in malolactic fermentation to provide bouquet and for pH adjustment. 

Poly(malic acid) is of pharmaceutical interest because its chemical derivatives may harbor both tissue-specific homing molecules and therapeutic effectors to be used for tissue (tumor) targeting in chemotherapy [2]. Because of its efficient production by fermentation, its biodegradability and nontoxicity, it is also considered as raw material in the industrial production of detergents, glues, and plastic materials. 

The following chapters will be devoted to the production of j8-poly(L-malic acid) or its salt by fermentation, its Isolation, and physico-chemical characterization. The biosynthesis, degradation, and presumed physiological role will be also considered. 

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). 

The M-L fermentation causes several beneficial changes in these high acid, low pH wines, among them a decrease in acidity and an increase in the pH. The effect of the conversion of malic acid to lactic acid on the total acidity of native and hybrid wines is shown in Table VIII. The total acidity decreased to the range 0.6-0.8 gram/100 ml which is considered desirable in these native wines. This conversion is of particular significance in regard to flavor since lactic is less sour than malic at the same titratable acidity and the same pH (63). 

The bacterial conversion of malic acid to lactic acid and carbon dioxide has been recognized since 1890 and is referred to as the malo-lactic fermentation. This conversion has been promoted under controlled conditions in the cooler viticultural regions of the world where grapes mature with excessive amounts of malic acid which causes taste imbalance... 

Vaughn, R. H., Tchelistcheff, A., Studies on the Malic Acid Fermentation... 

Malic Acid. This is seldom determined quantitatively in winery practice. However, qualitative paper chromatography is often done to follow malo-lactic fermentation. Using n-butyl alcohol and formic acid (80), the Rf values are tartaric 0.28, citric 0.45, malic 0.51, ethyl acid tartrate 0.59, lactic acid 0.78, succinic 0.78, and ethyl acid malate 0.80. 

Practical and fundamental aspects of malo-lactic fermentation are given. Conditions which winemakers can use for better control of the fermentation, including detailed procedures for inoculation with Leuconostoc oenos ML 34 and for inhibition with fumaric acid, are presented. New information on the role of malic acid decarboxylation in bacterial metabolism and on the enzymatics of malic acid decarboxylation are reviewed. The malic acid decarboxylation seems to involve two pathways a direct decarboxylation of malic to lactic acid with NAD as a coenzyme and a concurrent but small oxidative decarboxylation to pyruvic acid and NADH. How these pathways can bring about the marked stimulation of bacterial growth rate by the malo-lactic reaction and their negligible effect on growth yield are discussed. 

In addition to malo-lactic fermentation, another biological method for deacidification of high-acid must is to use malic acid-metabolizing Schizo-saccharomyces yeast for the alcoholic fermentation. Benda and Schmidt (33) have selected strains of these yeasts which produce wines with no off-flavors. In using some of these same strains we have also been able to make wines of sound character (18). 

Detection of Malo-Lactic Fermentation. It is imperative that the winemaker, to control malo-lactic fermentation, has a satisfactory method for its detection. Disappearance of malic acid is the indication of the fermentation, but the formation of lactic acid is not sufficient evidence since it might also be formed by yeast and by bacteria from other carbohydrate sources. The rate of conversion of malic acid is expected to reflect bacterial metabolism and growth. In New York State wines, Rice and Mattick (41) showed bacterial growth (as measured by viable count) to be more or less exponential to 106-107 cells/ml, preceding disappearance of malic acid. The rate of loss of malic acid is probably also exponential. Malic acid seems to disappear so slowly that its loss is not detected until a bacterial population of about 106-107 cells/ml is reached then it seems to disappear so rapidly that its complete loss is detected within a few days (41). Rice and Mattick (41) also showed a slight increase in bacterial population for a few days following this. 

For faster results, thin layer chromatography has been used (66), but we are not confident that lower levels of malic acid (0.06% ) (cf. Ref. 11), sometimes found in California wine before malo-lactic fermentation, are easily detected by this means. Malic acid can be more precisely measured by using the quantitative enzymatic method (67). Only the l isomer, the natural form present in grapes and wine, is detected by this method. 

The NADH-forming activity described here is different from the classical malic enzyme activity found by London et al. (95) in Lacto-badUus casei. In their system, NADH is a major end product and detectable by spectrophotometry while lactic acid is only a minor product. L. casei uses malic acid as an energy source with carbon dioxide, acetate, and ethanol as the main fermentation products. The optimal pH... 

For discussion of three aspects of malo-lactic fermentation not presented here, see Refs. 4 and 96. These are the relationship between malo-lactic fermentation and the yeast strain used in the alcoholic fermentation inducibility of the malic decomposing enzyme(s) and the role of oxaloacetic acid in the pathway of conversion of malic acid to lactic acid (cf. Ref. 76). 

The literature concerning malo—lactic fermentation—bacterial conversion of L-malic acid to L-lactic acid and carbon dioxide in wine—is reviewed, and the current concept of its mechanism is presented. The previously accepted mechanism of this reaction was proposed from work performed a number of years ago subsequently, several workers have presented data which tend to discount it. Currently, it is believed that during malo-lactic fermentation, the major portion of malic acid is directly decarboxylated to lactic acid while a small amount of pyruvic acid (and reduced coenzyme) is formed as an end product, rather than as an intermediate. It is suspected that this small amount of pyruvic acid has extremely important consequences on the intermediary metabolism of the bacteria. 

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. 

Considering the malo-lactic fermentation microbiologically, several factors are apparent. For example, the enzyme cofactor nicotinamide-adenine dinucleotide (NAD) is required for completion of the reaction, although there is no net oxidation-reduction change in proceeding from L-malic acid to L-lactic acid. Classically, the involvement of NAD in an... 

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