Uses

Used in Food Industry:
Lactic acid is used as a flavor agent, preservative, and acidity adjuster in foods. It is used in Spanish olives to prevent spoilage and provide flavor, in dry egg powder to improve dispersion and whipping properties, in cheese spreads, and in salad dressing mixes.
Used in Pharmaceutical Industry:
Lactic acid is used as a pH-adjusting agent in the beverage sector and as a preservative in the food industry. It is included in the Generally Recognized as Safe (GRAS) list by the U.S. Food and Drug Administration and was deemed safe by the European Food Safety Authority.
Used in Cosmetics:
Lactic acid (sodium lactate) is a multi-purpose ingredient used as a preservative, exfoliant, moisturizer, and to provide acidity to a formulation. It has better water intake than glycerin and can increase the water-retention capacity of the stratum corneum. Continuous use of preparations formulated with lactic acid in concentrations ranging between 5 and 12 percent can provide a mild to moderate improvement in fine wrinkling and promote softer, smoother skin. Its exfoliating properties can help in the process of removing excess pigment from the surface of the skin, as well as improving skin texture and feel.
Used in Polymer Production:
Nonfood use of lactic acid for polymer production contributes to its growing consumption. Biodegradable polylactic acid is considered an environmentally friendly alternative to other plastics from petroleum. It is used in various fields, including drug delivery systems, medical devices, fibers, and packaging materials.
Used in Industrial Applications:
Lactic acid showed good depressing effect on hornblende, pyroxene, and biotite during the flotation of hematite and ilmenite minerals.
Used in Chemical Synthesis:
Lactic acid can be produced via chemical synthesis or carbohydrate fermentation. It is used as a solvent, in manufacturing confectionery, and in medicine. It is also used to make cultured dairy products and chemicals.

Production Methods

Lactic acid is prepared by the fermentation of carbohydrates, such as glucose, sucrose, and lactose, with Bacillus acidi lacti or related microorganisms. On a commercial scale, whey, corn starch, potatoes, or molasses are used as a source of carbohydrate. Lactic acid may also be prepared synthetically by the reaction between acetaldehyde and carbon monoxide at 130–200°C under high pressure, or by the hydrolysis of hexoses with sodium hydroxide. Lactic acid prepared by the fermentation of sugars is levorotatory; lactic acid prepared synthetically is racemic. However, lactic acid prepared by fermentation becomes dextrorotatory on dilution with water owing to the hydrolysis of (R)-lactic acid lactate to (S)- lactic acid.

Biotechnological Production

Lactic acid is produced biotechnologically in general by fermentation of lactic acid bacteria. More information about this process and new trends are described later in this chapter.

Air & Water Reactions

Soluble in water.

Reactivity Profile

Lactic acid is a carboxylic acid. Carboxylic acids donate hydrogen ions if a base is present to accept them. They react in this way with all bases, both organic (for example, the amines) and inorganic. Their reactions with bases, called "neutralizations", are accompanied by the evolution of substantial amounts of heat. Neutralization between an acid and a base produces water plus a salt. Carboxylic acids with six or fewer carbon atoms are freely or moderately soluble in water; those with more than six carbons are slightly soluble in water. Soluble carboxylic acid dissociate to an extent in water to yield hydrogen ions. The pH of solutions of carboxylic acids is therefore less than 7.0. Many insoluble carboxylic acids react rapidly with aqueous solutions containing a chemical base and dissolve as the neutralization generates a soluble salt. Carboxylic acids in aqueous solution and liquid or molten carboxylic acids can react with active metals to form gaseous hydrogen and a metal salt. Such reactions occur in principle for solid carboxylic acids as well, but are slow if the solid acid remains dry. Even "insoluble" carboxylic acids may absorb enough water from the air and dissolve sufficiently in Lactic acid to corrode or dissolve iron, steel, and aluminum parts and containers. Carboxylic acids, like other acids, react with cyanide salts to generate gaseous hydrogen cyanide. The reaction is slower for dry, solid carboxylic acids. Insoluble carboxylic acids react with solutions of cyanides to cause the release of gaseous hydrogen cyanide. Flammable and/or toxic gases and heat are generated by the reaction of carboxylic acids with diazo compounds, dithiocarbamates, isocyanates, mercaptans, nitrides, and sulfides. Carboxylic acids, especially in aqueous solution, also react with sulfites, nitrites, thiosulfates (to give H2S and SO3), dithionites (SO2), to generate flammable and/or toxic gases and heat. Their reaction with carbonates and bicarbonates generates a harmless gas (carbon dioxide) but still heat. Like other organic compounds, carboxylic acids can be oxidized by strong oxidizing agents and reduced by strong reducing agents. These reactions generate heat. A wide variety of products is possible. Like other acids, carboxylic acids may initiate polymerization reactions; like other acids, they often catalyze (increase the rate of) chemical reactions. Slowly corrodes most metals [USCG, 1999].

Health Hazard

Inhalation of mist causes coughing and irritation of mucous membranes. Ingestion, even of diluted preparations, has a corrosive effect on the esophagus and stomach. Contact with more concentrated solutions can cause severe burns of skin or eye.

Fire Hazard

Combustible material: may burn but does not ignite readily. When heated, vapors may form explosive mixtures with air: indoors, outdoors and sewers explosion hazards. Contact with metals may evolve flammable hydrogen gas. Containers may explode when heated. Runoff may pollute waterways. Substance may be transported in a molten form.

Pharmaceutical Applications

Lactic acid is used in beverages, foods, cosmetics, and pharmaceuticals as an acidifying agent and acidulant. In topical formulations, particularly cosmetics, it is used for its softening and conditioning effect on the skin. Lactic acid may also be used in the production of biodegradable polymers and microspheres, such as poly(D-lactic acid), used in drug delivery systems. Lactic acid is also used as a food preservative. Therapeutically, lactic acid is used in injections, in the form of lactate, as a source of bicarbonate for the treatment of metabolic acidosis; as a spermicidal agent; in pessaries for the treatment of leukorrhea; in infant feeds; and in topical formulations for the treatment of warts.

Biochem/physiol Actions

In animals, lactic acid is a metabolic compound produced by proliferating cells and during anaerobic conditions such as strenuous exercise. Lactic acid can be oxidized back to pyruvate or converted to glucose via gluconeogenesis. Lactic acid is preferentially metabolized by neurons in several mammal species and during early brain development.

Safety

Lactic acid occurs in appreciable quantities in the body as an end product of the anaerobic metabolism of carbohydrates and, while harmful in the concentrated form , can be considered nontoxic at the levels at which it is used as an excipient. A 1% v/v solution, for example, is harmless when applied to the skin. There is evidence that neonates have difficulty in metabolizing (R)-lactic acid, and this isomer and the racemate should therefore not be used in foods intended for infants aged less than 3 months old. There is no evidence that lactic acid is carcinogenic, teratogenic, or mutagenic. LD50 (guinea pig, oral): 1.81 g/kg LD50 (mouse, oral): 4.88 g/kg LD50 (mouse, SC): 4.5 g/kg LD50 (rat, oral): 3.73 g/kg

storage

Lactic acid is hygroscopic and will form condensation products such as polylactic acids on contact with water. The equilibrium between the polylactic acids and lactic acid is dependent on concentration and temperature. At elevated temperatures lactic acid will form lactide, which is readily hydrolyzed back to lactic acid. Lactic acid should be stored in a well-closed container in a cool, dry place.

Incompatibilities

Incompatible with oxidizing agents, iodides, and albumin. Reacts violently with hydrofluoric acid and nitric acid.

Regulatory Status

GRAS listed. Accepted for use as a food additive in Europe. Included in the FDA Inactive Ingredients Database (IM, IV, and SC injections; oral syrups and tablets; topical and vaginal preparations). Included in medicines licensed in the UK. Included in the Canadian List of Acceptable Non-medicinal Ingredients.

Check Digit Verification of cas no

The CAS Registry Mumber 50-21-5 includes 5 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 2 digits, 5 and 0 respectively; the second part has 2 digits, 2 and 1 respectively.
Calculate Digit Verification of CAS Registry Number 50-21:
(4*5)+(3*0)+(2*2)+(1*1)=25
25 % 10 = 5
So 50-21-5 is a valid CAS Registry Number.

InChI:InChI=1/C3H6O3/c1-2(4)3(5)6/h2,4H,1H3,(H,5,6)/p-1/t2-/m1/s1