|Jmol-3D images||Image 1
|Molar mass||162.27 g mol−1|
|Density||1.112 g cm−3|
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Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Allicin is an organosulfur compound obtained from garlic, a species in the family Alliaceae. It was first isolated and studied in the laboratory by Chester J. Cavallito and John Hays Bailey in 1944. This colorless liquid has a distinctively pungent smell. This compound exhibits antibacterial and anti-fungal properties. Allicin is garlic's defense mechanism against attacks by pests.
Structure and occurrence
Allicin features the thiosulfinate functional group, R-S(O)-S-R. The compound is not present in garlic unless tissue damage occurs, and is formed by the action of the enzyme alliinase on alliin. Allicin is chiral but occurs naturally only as a racemate. The racemic form can also be generated by oxidation of diallyl disulfide:
- (SCH2CH=CH2)2 + RCO3H → CH2=CHCH2S(O)SCH2CH=CH2 + RCO2H
Alliinase is irreversibly deactivated below pH 3; as such, allicin is generally not produced in the body from the consumption of fresh or powdered garlic. Furthermore, allicin can be unstable, breaking down within 16 h at 23 °C.
Potential health benefits
||This section needs more medical references for verification or relies too heavily on primary sources. (September 2013)|
Several animal studies published between 1995 and 2005 indicate that allicin may reduce atherosclerosis and fat deposition, normalize the lipoprotein balance, decrease blood pressure, have anti-thrombotic and anti-inflammatory activities, and function as an antioxidant to some extent. Other animal studies have shown a strong oxidative effect in the gut that can damage intestinal cells, though many of these results were obtained by excessive amounts of allicin, which has been clearly shown to have some toxicity at high amounts, or by physically injecting the lumen itself with allicin, which may not be indicative of what would happen via oral ingestion of allicin or garlic supplements. A randomized clinical trial funded by the National Institutes of Health (NIH) in the United States and published in the Archives of Internal Medicine in 2007 found that the consumption of garlic in any form did not reduce blood cholesterol levels in patients with moderately high baseline cholesterol levels. The fresh garlic used in this study contained substantial levels of allicin, so the study casts doubt on the ability of allicin when taken orally to reduce blood cholesterol levels in human subjects.
In 2009, Vaidya, Ingold and Pratt clarified the mechanism of the antioxidant activity of garlic, such as trapping damaging free radicals. When allicin decomposes, it forms 2-propenesulfenic acid, and this compound is what binds to the free-radicals. The 2-propenesulfenic formed when garlic is cut or crushed has a lifetime of less than one second.
||This section needs more medical references for verification or relies too heavily on primary sources. (September 2013)|
Allicin has been found to have numerous antimicrobial properties, and has been studied in relation to both its effects and its biochemical interactions. One potential application is in the treatment of methicillin-resistant Staphylococcus aureus (MRSA), an increasingly prevalent concern in hospitals. A screening of allicin against 30 strains of MRSA found high level of antimicrobial activity, including against strains that are resistant to other chemical agents. Of the strains tested, 88% had minimum inhibitory concentrations for allicin liquids of 16 mg/L, and all strains were inhibited at 32 mg/L. Furthermore, 88% of clinical isolates had minimum bactericidal concentrations of 128 mg/L, and all were killed at 256 mg/L. Of these strains, 82% showed intermediate or full resistance to mupirocin. This same study examined use of an aqueous cream of allicin, and found it somewhat less effective than allicin liquid. At 500 mg/L, however, the cream was still active against all the organisms tested—which compares well with the 20 g/L mupirocin currently used for topical application.
A water-based formulation of purified allicin was found to be more chemically stable than other preparations of garlic extracts. They proposed that the stability may be due to the hydrogen bonding of water to the reactive oxygen atom in allicin and also to the absence of other components in crushed garlic that destabilize the molecule.
Although there are preliminary studies indicating some potential benefit of garlic in treating the common cold,  a 2012 report in the Cochrane Database of Systematic Reviews concluded that "there is insufficient clinical trial evidence regarding the effects of garlic in preventing or treating the common cold. A single trial - The trial that relied on self reported episodes of the common cold but was of reasonable quality in terms of randomisation and allocation concealment, suggested that garlic may prevent occurrences of the common cold but more studies are needed to validate this finding. Claims of effectiveness appear to rely largely on poor-quality evidence." Similar conclusions are voiced in a 2013 report, which states "Garlic as a preventative or treatment option for the common cold ... could not be recommended, as only one relatively small trial evaluated the effects separately. Garlic might be effective in some areas of clinical practice, but the evidence levels were low, so further researches should be well designed using rigorous method to avoid potential biases"
|Wikimedia Commons has media related to allicin.|
- Allyl isothiocyanate, the active piquant chemical in mustard, radishes, horseradish and wasabi
- Capsaicin, the active piquant chemical in chili peppers
- Piperine, the active piquant chemical in black pepper
- syn-Propanethial-S-oxide, the chemical found in onions
- List of phytochemicals in food
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