| Diacetyl[1] | |
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2,3-Butanedione |
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Other names
Diacetyl |
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| Identifiers | |
| CAS number | 431-03-8 |
| PubChem | 650 |
| ChemSpider | 630 |
| UNII | K324J5K4HM |
| KEGG | C00741 |
| ChEBI | CHEBI:16583 |
| ChEMBL | CHEMBL365809 |
| Jmol-3D images | Image 1 |
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| Properties | |
| Molecular formula | C4H6O2 |
| Molar mass | 86.0892 g/mol |
| Appearance | Yellowish green liquid |
| Density | 0.990 g/mL at 15 °C |
| Melting point |
−2 to −4 °C |
| Boiling point |
88 °C |
| Solubility in water | Soluble in 4 parts |
| Hazards | |
| MSDS | External MSDS |
| R-phrases | R10 R22 R36 R37 R38 |
| S-phrases | S9 S16 S33 |
| Main hazards | Harmful, flammable |
| (verify) (what is: /?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
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| Infobox references | |
Diacetyl (IUPAC systematic name: butanedione or 2,3-butanedione) is a natural byproduct of fermentation. It is a vicinal diketone (two C=O groups, side-by-side) with the molecular formula C4H6O2. Diacetyl occurs naturally in alcoholic beverages and is added to some foods to impart a buttery flavor.
Contents |
Diacetyl and acetoin are two compounds that give butter its characteristic taste. Because of this, manufacturers of margarines or similar oil-based products typically add diacetyl and acetoin (along with beta carotene for the yellow color) to make the final product butter-flavored, because it would otherwise be relatively tasteless.[2]
At low levels, diacetyl contributes a slipperiness to the feel of the alcoholic beverage in the mouth. As levels increase, it imparts a buttery or butterscotch flavor (butterscotch itself may have no diacetyl in it at all).
In some styles of beer (e.g. in most beers produced in the British Isles, such as English Pale ales) the presence of diacetyl can be acceptable or desirable at low or, in some cases, moderate levels. In other styles the presence of diacetyl is considered a flaw or undesirable.[3]
Diacetyl is produced during fermentation as a by-product of valine synthesis, when yeast produces α-acetolactate, which escapes the cell and is spontaneously decarboxylated into diacetyl. The yeast then absorbs the diacetyl, and reduces the ketone groups to form acetoin and 2,3-butanediol, relatively flavorless compounds.
Beer sometimes undergoes a diacetyl rest, in which its temperature is raised slightly for two or three days after fermentation is complete, to allow the yeast to absorb the diacetyl it produced earlier in the fermentation cycle. The makers of some wines, such as Chardonnay, deliberately promote the production of diacetyl because of the feel and flavor it imparts. It is present in many California chardonnays known as "Butter Bombs," although there is a growing trend back toward the more traditional French styles.
Concentrations from 0.005 mg/L to 1.7 mg/L were measured in chardonnay wines, and the amount needed for the flavor to be noticed is at least 0.2 mg/L.[4][5]
Sour (cultured) cream, cultured buttermilk, and cultured butter are produced by inoculating pasteurized cream or milk with a lactic starter culture, churning (agitating) and holding the milk until a desired pH drop (or increase in acidity) is attained. Cultured cream, cultured butter, and cultured buttermilk owe their tart flavour to lactic acid bacteria and their buttery aroma and taste to diacetyl.[6]
Hexanol and 2,3-butanedione are strong inhibitors of the CO2-sensitive neurons in the fruit fly. CO2 emitted in human breath is the main attractant for the Culex mosquito to find people.[7]
The United States National Institute for Occupational Safety and Health has suggested that diacetyl, when used in artificial butter flavoring (as used in many consumer foods), may be hazardous when heated and inhaled over a long period.
Workers in several factories that manufacture artificial butter flavoring have been diagnosed with bronchiolitis obliterans, a rare and serious disease of the lungs. The cases found have been mainly in young, healthy, non-smoking males. There are no known cures for bronchiolitis obliterans except for lung transplantation.
While several authorities have called the disease "Popcorn Worker's Lung," a more accurate term suggested by other doctors may be more appropriate, since the disease can occur in any industry working with diacetyl: diacetyl-induced bronchiolitis obliterans.
After the workers filed a lawsuit against the manufacturers, the United States Environmental Protection Agency began an investigation into the chemical properties of microwave popcorn butter flavoring. In March 2004, former microwave popcorn plant employee Eric Peoples, of Joplin, Missouri, was awarded $20 million for permanent lung-injuries sustained while on the job.[8] On July 19, 2005, jurors awarded $2.7 million to another popcorn plant worker in Missouri for his claim of diacetyl-induced respiratory problems.[9]
On July 26, 2006, the International Brotherhood of Teamsters and the United Food and Commercial Workers petitioned the U.S. Occupational Safety and Health Administration to promulgate an emergency temporary standard to protect workers from the deleterious health effects of inhaling diacetyl vapors.[10] The petition was followed by a letter of support signed by more than thirty prominent scientists.[11] The matter is under consideration. On 21 January 2009, OSHA issued an advance notice of proposed rulemaking for regulating exposure to diacetyl.[12] The notice requests respondents to provide input regarding adverse health effects, methods to evaluate and monitor exposure, the training of workers. That notice also solicited input regarding exposure and health effects of acetoin, acetaldehyde, acetic acid and furfural.[13]
There are currently two bills in the California Legislature to ban the use of diacetyl.[14][15][16]
A 2010 OSHA Safety and Health Information Bulletin and companion Worker Alert recommend that employers use safety measures to avoid exposing employees to the potentially deadly effects of butter flavorings and other flavoring substances containing diacetyl or its substitutes.[17]
Dr. Cecile Rose, pulmonary specialist at Denver's National Jewish Medical and Research Center, in a letter, warned federal agencies or regulators that consumers, not just factory workers, are in danger of contracting bronchiolitis obliterans from fumes produced by microwaving popcorn containing diacetyl. David Michaels of the George Washington University School of Public Health first published Rose's letter on his blog.[18] However, the only sample data known-to-date is the case where a consumer, who ate at least two bags of buttery microwave popcorn daily for 10 years, became diagnosed with the same disease affecting workers exposed to the substance, bronchiolitis obliterans.[19] His lung problems were linked to breathing the vapors; although rare, the reported man's kitchen also had diacetyl levels comparable to those in popcorn plants.[19]
The Flavor and Extract Manufacturers Association recommended reducing diacetyl in butter flavorings (24 September 2007). The Pop Weaver brand popcorn from the Weaver Popcorn Company of Indianapolis was the first to replace its butter flavoring with a new ingredient.[20] Weaver makes also the Trail's End brand of popcorn, currently sold by the Boy Scouts of America and Scouts Canada. In a press release dated December 17, 2007, ConAgra Foods, maker of Orville Redenbacher's and Act II microwave popcorn brands, announced it had removed added diacetyl from all of its butter-flavored microwave popcorn varieties. The new products began hitting store shelves as early as October 2007.[21]
The European Commission has declared that diacetyl is legal for use as a flavouring substance in all EU states.[22] As a diketone, diacetyl is included in the EU's flavouring classification Flavouring Group Evaluation 11 (FGE.11). A Scientific Panel of the EU Commission evaluated six flavouring substances (not including diacetyl) from FGE.11 in 2004.[23] As part of this study, the Panel reviewed available studies on several other flavourings in FEG.11, including diacetyl. Based on the available data, the Panel reiterated the finding that there were no safety concerns for diacetyl's use as a flavouring. As a result of the Panel's 2004 study, acetylacetone (FL 07.191) was found to be genotoxic in vitro and in vivo, and was therefore deleted from the register of permitted flavouring substances.[24] Recently, the European Food Safety Authority (EFSA), the EU's food safety regulatory body, stated that its scientific panel on food additives and flavourings (AFC) was evaluating diacetyl along with other flavourings as part of a larger study. "The experts of the EFSA AFC panel and its working group on food additives will look at this issue to see if new scientific evidence is available that may require further actions. If the experts conclude that consumer exposure to diacetyl can reach levels well above those considered as safe and, that a possible health risk for consumers cannot be excluded when inhaling diacetyl, EFSA will give priority to the re-evaluation of this substance and provide detailed scientific advice."[25]