Sorbic acid, or 2,4-hexadienoic acid, is a natural

organic compound In chemistry, organic compounds are generally any chemical compounds that contain carbon- hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. Th ...

used as a food

preservative A preservative is a substance or a chemical that is added to products such as food products, beverages, pharmaceutical drugs, paints, biological samples, cosmetics, wood, and many other products to prevent decomposition by microbial growth or ...

. It has the

chemical formula In chemistry, a chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, ...

and the structure . It is a colourless solid that is slightly soluble in water and

sublimes Sublimation is the transition of a substance directly from the solid to the gas state, without passing through the liquid state. Sublimation is an endothermic process that occurs at temperatures and pressures below a substance's triple point i ...

readily. It was first isolated from the unripe berries of the ''Sorbus aucuparia'' ( rowan tree), hence its name.

Production

The traditional route to sorbic acid involves condensation of malonic acid and crotonaldehyde. It can also be prepared from isomeric hexadienoic acids, which are available via a nickel-catalyzed reaction of allyl chloride, acetylene, and

carbon monoxide Carbon monoxide ( chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the si ...

. The route used commercially, however, is from crotonaldehyde and ketene. An estimated 30,000 tons are produced annually.

History

Sorbic acid was isolated in 1859 by

distillation Distillation, or classical distillation, is the process of separating the components or substances from a liquid mixture by using selective boiling and condensation, usually inside an apparatus known as a still. Dry distillation is the he ...

of rowanberry oil by

A. W. von Hofmann August Wilhelm von Hofmann (8 April 18185 May 1892) was a German chemist who made considerable contributions to organic chemistry. His research on aniline helped lay the basis of the aniline-dye industry, and his research on coal tar laid the g ...

. This affords

parasorbic acid Parasorbic acid is the cyclic lactone of sorbic acid. Thermal treatment or hydrolysis converts the lactone to sorbic acid. Toxicity Parasorbic acid is toxic and causes indigestion and nausea, however cooking and exposure to moisture convert i ...

, the

lactone Lactones are cyclic carboxylic esters, containing a 1-oxacycloalkan-2-one structure (), or analogues having unsaturation or heteroatoms replacing one or more carbon atoms of the ring. Lactones are formed by intramolecular esterification of the co ...

of sorbic acid, which he converted to sorbic acid by hydrolysis. Its antimicrobial activities were discovered in the late 1930s and 1940s, and it became commercially available in the late 1940s and 1950s. Beginning in the 1980s, sorbic acid and its salts were used as inhibitors of ''

Clostridium botulinum ''Clostridium botulinum'' is a Gram-positive, rod-shaped, anaerobic, spore-forming, motile bacterium with the ability to produce the neurotoxin botulinum. The botulinum toxin can cause botulism, a severe flaccid paralytic disease in humans ...

'' in meat products to replace the use of nitrites, which can produce carcinogenic nitrosamines.

Properties and uses

With a p''K''_a of 4.76, sorbic acid is about as acidic as acetic acid. Sorbic acid and its salts, especially potassium sorbate and

calcium sorbate Calcium sorbate is the calcium salt of sorbic acid. Calcium sorbate is a polyunsaturated fatty acid salt. It is a commonly used food preservative Food preservation includes processes that make food more resistant to microorganism growth a ...

, are antimicrobial agents often used as preservatives in food and drinks to prevent the growth of mold,

yeast Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are estimated to consti ...

, and

fungi A fungus (plural, : fungi or funguses) is any member of the group of Eukaryote, eukaryotic organisms that includes microorganisms such as yeasts and Mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified ...

. In general the salts are preferred over the acid form because they are more soluble in water, but the active form is the acid. The optimal pH for the antimicrobial activity is below pH 6.5. Sorbates are generally used at concentrations of 0.025% to 0.10%. Adding sorbate salts to food will, however, raise the pH of the food slightly so the pH may need to be adjusted to assure safety. It is found in foods such as various kinds of cheese, bread, muffins, donuts, pies, cookies, protein bars, syrups, lemonades, fruit juices, dried meats, sausages, nuggets, burgers, sandwiches, tacos, pizzas, smoked fish, margarine, sauces, soups, and more. The E numbers are: * E200 Sorbic acid * E201 Sodium sorbate * E202 Potassium sorbate * E203

Calcium sorbate Calcium sorbate is the calcium salt of sorbic acid. Calcium sorbate is a polyunsaturated fatty acid salt. It is a commonly used food preservative Food preservation includes processes that make food more resistant to microorganism growth a ...

Some molds (notably some ''

Trichoderma ''Trichoderma'' is a genus of fungi in the family Hypocreaceae that is present in all soils, where they are the most prevalent culturable fungi. Many species in this genus can be characterized as opportunistic avirulent plant symbionts. This ...

'' and ''

Penicillium ''Penicillium'' () is a genus of ascomycetous fungi that is part of the mycobiome of many species and is of major importance in the natural environment, in food spoilage, and in food and drug production. Some members of the genus produce ...

'' strains) and

s are able to detoxify sorbates by decarboxylation, producing ''trans''-1,3-pentadiene. The pentadiene manifests as a typical odor of kerosene or

petroleum Petroleum, also known as crude oil, or simply oil, is a naturally occurring yellowish-black liquid mixture of mainly hydrocarbons, and is found in geological formations. The name ''petroleum'' covers both naturally occurring unprocessed crude ...

. Other detoxification reactions include reduction to 4- hexenol and 4-hexenoic acid. Sorbic acid can also be used as an additive for cold rubber, and as an intermediate in the manufacture of some plasticizers and lubricants.

Safety

Sorbic acid and sorbate salts have a very low mammalian toxicity and carcinogenicity. Its is estimated to be between 7.4 and 10 g/kg.

References

External links