Diacetyl

Diacetyl
IUPAC name Butane-2,3-dione
Other names Diacetyl Biacetyl Dimethyl diketone 2,3-Diketobutane
Identifiers
CAS number	431-03-8 Y
PubChem	650
ChemSpider	630 Y
UNII	K324J5K4HM Y
KEGG	C00741 Y
ChEBI	CHEBI:16583 Y
ChEMBL	CHEMBL365809 Y
Jmol-3D images	Image 1
SMILES O=C(C(=O)C)C
InChI InChI=1S/C4H6O2/c1-3(5)4(2)6/h1-2H3 Y Key: QSJXEFYPDANLFS-UHFFFAOYSA-N Y InChI=1/C4H6O2/c1-3(5)4(2)6/h1-2H3 Key: QSJXEFYPDANLFS-UHFFFAOYAX
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
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Diacetyl (IUPAC systematic name: butanedione or butane-2,3-dione) 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.

In Food Products

Diacetyl and acetoin are two compounds that give butter its characteristic taste. Because of this, manufacturers of artificial butter flavoring, 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.

In Alcoholic Beverages

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, its presence is considered a flaw or undesirable.

Diacetyl is produced during fermentation as a byproduct 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.^{[citation needed]}

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.

In Milk Products

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.

Mosquito Repellent

1-Hexanol and diacetyl are strong inhibitors of the CO₂-sensitive neurons in the Drosophila melanogaster fruit fly and the Culex mosquito, a vector of several deadly diseases. Fruit flies tend to avoid CO₂, but exhaled CO₂ is the main attractant for the Culex.

Safety

Worker Safety

The United States National Institute for Occupational Safety and Health has suggested 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, nonsmoking males. As with other end-stage lung diseases, transplantation is currently the most viable treatment option. However, lung transplant rejection is very common and happens to be another setting in which bronchiolitis obliterans is known to occur.

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.

In 2006, the International Brotherhood of Teamsters and the United Food and Commercial Workers petitioned the U.S. OSHA to promulgate an emergency temporary standard to protect workers from the deleterious health effects of inhaling diacetyl vapors. The petition was followed by a letter of support signed by more than 30 prominent scientists. The matter is under consideration. On 21 January 2009, OSHA issued an advance notice of proposed rulemaking for regulating exposure to diacetyl. 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.

Two bills in the California Legislature seek to ban the use of diacetyl.

A 2010 OSHA Safety and Health Information Bulletin and companion Worker Alert recommend 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.

A preliminary in vitro study, published in 2012, suggests that diacetyl may exacerbate the effects of beta-amyloid aggregation, a process linked to Alzheimer's disease.

Consumer Safety

In 2007, the Flavor and Extract Manufacturers Association recommended reducing diacetyl in butter flavorings. Manufacturers of butter flavored popcorn including Pop Weaver, Trail's End, and ConAgra Foods (maker of Orville Redenbacher's and Act II) began removing diacetyl as an ingredient from their products.

In 2012, Wayne Watson a regular microwavable popcorn consumer for years, was awarded $7.27 million in damages from a federal jury in Denver, which decided his lung disease was caused by the chemicals in microwave popcorn and that the popcorn's manufacturer, Gilster-Mary Lee Corporation, and the grocery store that sold it should have warned him of its dangers.

European Union Regulation

The European Commission has declared diacetyl is legal for use as a flavouring substance in all EU states. 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. 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.

In 2007, the European Food Safety Authority (EFSA), the EU's food safety regulatory body, stated 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."

See also

• Bronchiolitis obliterans

External links

• Research project on diacetyl reduction during beer fermentation
• Toxicology data
• NIOSH Alert: Preventing Lung Disease and Workers who Use or Make Flavorings
• Harber P, Saechao K, Boomus C (2006). "Diacetyl-induced lung disease". Toxicol Rev 25 (4): 261–72. doi:10.2165/00139709-200625040-00006. PMID 17288497. 
• A Case of Regulatory Failure - Popcorn Workers Lung, from www.defendingscience.org.
• Scientists Urge Secretary of Labor to Protect Workers from Diacetyl, a press release from defendingscience.org. Links to studies on the health effects of diacetyl, and to a variety of related documents including the recent OSHA petition and the scientists' letter of support may be found here.
• Flavoring suspected in illness, Washington Post, May 7, 2007.
• NIOSH International Safety Card for 2,3-butanedione
• National Institute for Occupational Safety and Health - Flavorings-Related Lung Disease
• IFIC - Diacetyl