6915-15-7

White or nearly white, crystalline powder or granules having a slight odor and a strongly acidic taste. It is hygroscopic. The synthetic material produced commercially in Europe and the USA is a racemic mixture, whereas the naturally occurring material found in apples and many other fruits and plants is levorotatory.

White to nearly white crystals or crystal powder

A colorless crystalline carboxylic acid that is found in unripe fruits. It tastes of apples and is used in food flavorings.

ChEBI: A 2-hydroxydicarboxylic acid that is succinic acid in which one of the hydrogens attached to a carbon is replaced by a hydroxy group.

Malic acid is manufactured by hydrating maleic and fumaric acids in the presence of suitable catalysts. The malic acid formed is then separated from the equilibrium product mixture.

DL-malic acid as well as L-malic acid can be used in beverage, food, and animal nutrition. DL-malic acid is mainly derived from chemical synthesis, whereas L-malic acid is produced biotechnologically by enzymatic or fermentative processes.
Fumaric acid can be converted to L-malic acid using fumarases. Different microorganisms (e.g. Brevibacterium flavum, Brevibacterum ammoniagenes, and Corynebacterium species) are able to form naturally high amounts of fumarase intracellularly. For example, B. flavum has been immobilized in j-carrageenan and polyethyleneimine for whole-cell biocatalysis. A fumarase activity of 2.16 mmol.ml(gel)-1.h -1 at 55 C has been reported. This process has been used to produce 30 metric tons of L-malic acid per month in a continuous process with a 1,000 L column fed at a flow rate of 450 L.h-1 of 1 M sodium fumarate solution. Genetic engineering has been used to improve productivity, by which S. cerevisiae is modified to overexpress fumarase. With this method, a conversion rate of 65 mmol.g-1.h -1 has been observed.
Another possibility is the cultivation of an L-malic acid forming microorganism (e.g. Aspergillus flavus or Schizophyllum commune). The best results have been achieved by cultivation of A. flavus on glucose.Afinal product concentration of 113 g.L-1 with a yield of 1.26 mol of malic acid per mole of glucose and a productivity of 0.59 g.L-1.h-1 has been measured. Moreover, new biotechnological routes have been described using metabolically engineered S. cereviciae. In batch cultivations, concentrations up to 59 g.L-1 with a yield of 0.42 mol of malic acid per mole of glucose and a productivity of 0.19 g.L-1.h-1 have been observed.

Nonflammable

Malic acid is used in pharmaceutical formulations as a generalpurpose acidulant. It possesses a slight apple flavor and is used as a flavoring agent to mask bitter tastes and provide tartness. Malic acid is also used as an alternative to citric acid in effervescent powders, mouthwashes, and tooth-cleaning tablets.
In addition, malic acid has chelating and antioxidant properties. It may be used with butylated hydroxytoluene as a synergist in order to retard oxidation in vegetable oils. In food products it may be used in concentrations up to 420 ppm.
Therapeutically, malic acid has been used topically in combination with benzoic acid and salicylic acid to treat burns, ulcers, and wounds. It has also been used orally and parenterally, either intravenously or intramuscularly, in the treatment of liver disorders, and as a sialagogue.

Malic acid is a dicarboxylic acid and an important regulatory metabolite. It has been implicated in process of fruit ripening. Malic acid is important for the starch metabolism; low malic acid content results in transient accumulation of starch. Mitochondrial-malate metabolism modulates ADP-glucose pyrophosphorylase activity and redox status of plastids.

Malic acid is absorbed from the gastrointestinal tract from whence it is transported via the portal circulation to the liver. There are a few enzymes that metabolize malic acid. Malic enzyme catalyzes the oxidative decarboxylation of L-malate to pyruvate with concomitant reduction of the cofactor NAD+ (oxidized form of nicotinamide adenine dinucleotide) or NADP+ (oxidized form of nicotinamide adenine dinucleotide phosphate). These reactions require the divalent cations magnesium or manganese. Three isoforms of malic enzyme have been identified in mammals: a cytosolic NADP+-dependent malic enzyme, a mitochondrial NADP+- dependent malic enzyme and a mitochondrial NAD(P)+-dependent malic enzyme. The latter can use either NAD+ or NADP+ as the cofactor but prefers NAD+. Pyruvate formed from malate can itself be metabolized in a number of ways, including metabolism via a number of metabolic steps to glucose. Malate can also be metabolized to oxaloacetate via the citric acid cycle. The mitochondrial malic enzyme, particularly in brain cells may play a key role in the pyruvate recycling pathway, which utilizes dicarboxylic acids and substrates, such as glutamine, to provide pyruvate to maintain the citric acid cycle activity when glucose and lactate are low.

Malic acid is used in oral, topical, and parenteral pharmaceutical formulations in addition to food products, and is generally regarded as a relatively nontoxic and nonirritant material. However, concentrated solutions may be irritant.
LD₅₀ (rat, oral): 1.6 g/kg(3)
LD₅₀ (rat, IP): 0.1 g/kg

Malic acid is stable at temperatures up to 150°C. At temperatures above 150°C it begins to lose water very slowly to yield fumaric acid; complete decomposition occurs at about 180°C to give fumaric acid and maleic anhydride.
Malic acid is readily degraded by many aerobic and anaerobic microorganisms. Conditions of high humidity and elevated temperatures should be avoided to prevent caking.
The effects of grinding and humidity on malic acid have also been investigated.
The bulk material should be stored in a well-closed container, in a cool, dry place.

Crystallise the acid from acetone, then from acetone/CCl4, or from ethyl acetate by adding pet ether (b 60-70o). Dry it at 35o under 1mm pressure to avoid formation of the anhydride. [Beilstein 3 IV 1124.]

Malic acid can react with oxidizing materials. Aqueous solutions are mildly corrosive to carbon steels.

GRAS listed. Both the racemic mixture and the levorotatory isomer are accepted as food additives in Europe. The DL and L forms are included in the FDA Inactive Ingredients Database (oral preparations). Included in nonparenteral and parenteral medicines licensed in the UK. Included in the Canadian List of Acceptable Nonmedicinal Ingredients.