3-Hydroxybutanone
Encyclopedia
Acetoin , also known as 3-hydroxybutanone or acetyl methyl carbinol, with the molecular formula is C4H8O2. It is a colorless or pale yellow to green yellow liquid
with a pleasant buttery odor.
, a common precursor in the biosynthesis of branched chain amino acids. Owing to its neutral nature, production and excretion of acetoin during exponential growth prevents over acidification of the cytoplasm and the surrounding medium that would result from accumulation of acidic metabolic products such as acetate
and citrate
. Once superior carbon sources are exhausted, and the culture enters stationary phase, acetoin can be utilised in order to maintain the culture density. The conversion of acetoin into acetyl-CoA
is catalysed by the acetoin dehydrogenase
complex, following a mechanism largely analogous to the pyruvate dehydrogenase
complex; however, as acetoin is not a 2-oxoacid it does not undergo decarboxylation by the E1 enzyme, instead a molecule of acetaldehyde
is released.
In some bacteria acetoin can also be reduced to 2,3-butanediol
by acetoin reductase/2,3-butanediol dehydrogenase.
The Voges-Proskauer test is a commonly used microbiological test for acetoin production.
, is one of the compounds giving butter
its characteristic flavor
. Because of this, manufacturers of partially hydrogenated
oils
typically add acetoin and diacetyl (along with beta carotene for the yellow color) to the final product, which would otherwise be tasteless.
Acetoin is used as a food flavor
ing (in baked goods) and a fragrance. It can be found in apple
s, butter, yogurt, asparagus
, black currants, blackberry
, wheat
, broccoli
, brussels sprouts, cantaloupe
.
companies, acetoin was listed as one of the 599 additives to cigarettes.
Liquid
Liquid is one of the three classical states of matter . Like a gas, a liquid is able to flow and take the shape of a container. Some liquids resist compression, while others can be compressed. Unlike a gas, a liquid does not disperse to fill every space of a container, and maintains a fairly...
with a pleasant buttery odor.
Production in bacteria
Acetoin is a neutral, four carbon molecule used as an external energy store by a number of fermentive bacteria. Acetoin is produced by the decarboxylation of alpha-acetolactateAcetolactate
α-Acetolactic acid is a precursor in the biosynthesis of the branched chain amino acids valine and leucine. α-Acetolactic acid is produced from two molecules of pyruvic acid by acetolactate synthase. α-Acetolactic acid can also be decarboxylated by alpha-acetolactate decarboxylase to produce...
, a common precursor in the biosynthesis of branched chain amino acids. Owing to its neutral nature, production and excretion of acetoin during exponential growth prevents over acidification of the cytoplasm and the surrounding medium that would result from accumulation of acidic metabolic products such as acetate
Acetate
An acetate is a derivative of acetic acid. This term includes salts and esters, as well as the anion found in solution. Most of the approximately 5 billion kilograms of acetic acid produced annually in industry are used in the production of acetates, which usually take the form of polymers. In...
and citrate
Citrate
A citrate can refer either to the conjugate base of citric acid, , or to the esters of citric acid. An example of the former, a salt is trisodium citrate; an ester is triethyl citrate.-Other citric acid ions:...
. Once superior carbon sources are exhausted, and the culture enters stationary phase, acetoin can be utilised in order to maintain the culture density. The conversion of acetoin into acetyl-CoA
Acetyl-CoA
Acetyl coenzyme A or acetyl-CoA is an important molecule in metabolism, used in many biochemical reactions. Its main function is to convey the carbon atoms within the acetyl group to the citric acid cycle to be oxidized for energy production. In chemical structure, acetyl-CoA is the thioester...
is catalysed by the acetoin dehydrogenase
Acetoin dehydrogenase
Acetoin dehydrogenase or diacetyl reductase is an enzyme that catalyzes the transformation of acetoin to diacetyl....
complex, following a mechanism largely analogous to the pyruvate dehydrogenase
Pyruvate dehydrogenase
Pyruvate dehydrogenase complex is a complex of three enzymes that transform pyruvate into acetyl-CoA by a process called pyruvate decarboxylation. Acetyl-CoA may then be used in the citric acid cycle to carry out cellular respiration, and this complex links the glycolysis metabolic pathway to the...
complex; however, as acetoin is not a 2-oxoacid it does not undergo decarboxylation by the E1 enzyme, instead a molecule of acetaldehyde
Acetaldehyde
Acetaldehyde is an organic chemical compound with the formula CH3CHO or MeCHO. It is one of the most important aldehydes, occurring widely in nature and being produced on a large scale industrially. Acetaldehyde occurs naturally in coffee, bread, and ripe fruit, and is produced by plants as part...
is released.
In some bacteria acetoin can also be reduced to 2,3-butanediol
2,3-Butanediol
2,3-Butanediol is a chemical compound composed of carbon, hydrogen, and oxygen. Its formula is C4H10O2. It is one of the constitutional isomers of butanediol....
by acetoin reductase/2,3-butanediol dehydrogenase.
The Voges-Proskauer test is a commonly used microbiological test for acetoin production.
In food products
Acetoin, along with diacetylDiacetyl
Diacetyl is a natural byproduct of fermentation. It is a vicinal diketone with the molecular formula C4H6O2...
, is one of the compounds giving butter
Butter
Butter is a dairy product made by churning fresh or fermented cream or milk. It is generally used as a spread and a condiment, as well as in cooking applications, such as baking, sauce making, and pan frying...
its characteristic flavor
Flavor
Flavor or flavour is the sensory impression of a food or other substance, and is determined mainly by the chemical senses of taste and smell. The "trigeminal senses", which detect chemical irritants in the mouth and throat as well as temperature and texture, are also very important to the overall...
. Because of this, manufacturers of partially hydrogenated
Hydrogenation
Hydrogenation, to treat with hydrogen, also a form of chemical reduction, is a chemical reaction between molecular hydrogen and another compound or element, usually in the presence of a catalyst. The process is commonly employed to reduce or saturate organic compounds. Hydrogenation typically...
oils
Vegetable fats and oils
Vegetable fats and oils are lipid materials derived from plants. Physically, oils are liquid at room temperature, and fats are solid. Chemically, both fats and oils are composed of triglycerides, as contrasted with waxes which lack glycerin in their structure...
typically add acetoin and diacetyl (along with beta carotene for the yellow color) to the final product, which would otherwise be tasteless.
Acetoin is used as a food flavor
Flavor
Flavor or flavour is the sensory impression of a food or other substance, and is determined mainly by the chemical senses of taste and smell. The "trigeminal senses", which detect chemical irritants in the mouth and throat as well as temperature and texture, are also very important to the overall...
ing (in baked goods) and a fragrance. It can be found in apple
Apple
The apple is the pomaceous fruit of the apple tree, species Malus domestica in the rose family . It is one of the most widely cultivated tree fruits, and the most widely known of the many members of genus Malus that are used by humans. Apple grow on small, deciduous trees that blossom in the spring...
s, butter, yogurt, asparagus
Asparagus
Asparagus officinalis is a spring vegetable, a flowering perennialplant species in the genus Asparagus. It was once classified in the lily family, like its Allium cousins, onions and garlic, but the Liliaceae have been split and the onion-like plants are now in the family Amaryllidaceae and...
, black currants, blackberry
Blackberry
The blackberry is an edible fruit produced by any of several species in the Rubus genus of the Rosaceae family. The fruit is not a true berry; botanically it is termed an aggregate fruit, composed of small drupelets. The plants typically have biennial canes and perennial roots. Blackberries and...
, wheat
Wheat
Wheat is a cereal grain, originally from the Levant region of the Near East, but now cultivated worldwide. In 2007 world production of wheat was 607 million tons, making it the third most-produced cereal after maize and rice...
, broccoli
Broccoli
Broccoli is a plant in the cabbage family, whose large flower head is used as a vegetable.-General:The word broccoli, from the Italian plural of , refers to "the flowering top of a cabbage"....
, brussels sprouts, cantaloupe
Cantaloupe
"Rockmelon" redirects here, for the band see Rockmelons. See also Cantaloupe .Cantaloupe refers to a variety of Cucumis melo, a species in the family Cucurbitaceae which includes nearly all melons and squashes. Cantaloupes range in size from...
.
Cigarette additive
In a 1994 report released by five top cigaretteCigarette
A cigarette is a small roll of finely cut tobacco leaves wrapped in a cylinder of thin paper for smoking. The cigarette is ignited at one end and allowed to smoulder; its smoke is inhaled from the other end, which is held in or to the mouth and in some cases a cigarette holder may be used as well...
companies, acetoin was listed as one of the 599 additives to cigarettes.