Allicin

 ( Thiosulfinates ) 

Allicin is an organosulfur compound obtained from garlic and leeks. When fresh garlic is chopped or crushed, the enzyme alliinase converts alliin into allicin, which is responsible for the aroma of fresh garlic. Allicin is unstable and quickly changes into a series of other sulfur-containing compounds such as diallyl disulfide. Allicin is an antifeedant, i.e. the defense mechanism against attacks by pests on the garlic plant.

Allicin is an oily, slightly yellow liquid that gives garlic its distinctive odor. It is a thioester of sulfenic acid. It is also known as allyl thiosulfinate. Its biological activity can be attributed to both its antioxidant activity and its reaction with thiol-containing proteins.

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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.

Eric Block (2025). 9780854041909, Royal Society of Chemistry. ISBN 9780854041909

The racemic form can also be generated by oxidation of diallyl disulfide:

(1996). 9780471955122, Wiley. ISBN 9780471955122

(SCH₂CH=CH₂)₂ + 2 RCO₃H + H₂O → 2 CH₂=CHCH₂SOH + 2 RCO₂H

2 CH₂=CHCH₂SOH → CH₂=CHCH₂S(O)SCH₂CH=CH₂ + H₂O

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 hours at 23 °C.

(1996). 9780683181470, Williams and Wilkins. ISBN 9780683181470

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Biosynthesis

The biosynthesis of allicin commences with the conversion of cysteine into S-allyl-L-cysteine. Oxidation of this thioether gives the sulfoxide (alliin). The enzyme alliinase, which contains pyridoxal phosphate (PLP), cleaves alliin, generating allylsulfenic acid (CH₂=CHCH₂SOH), pyruvate, and ammonium ions. At room temperature, two molecules of allylsulfenic acid condense to form allicin.

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Research

Allicin has been studied for its potential to treat various kinds of multiple drug resistance bacterial infections, as well as viral and fungal infections in vitro, but as of 2016, the safety and efficacy of allicin to treat infections in people was unclear.

A Cochrane review found there to be insufficient clinical evidence regarding the effects of allicin in preventing or treating common cold.

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History

It was first isolated and studied in the laboratory by Chester J. Cavallito and John Hays Bailey in 1944. Allicin was discovered as part of efforts to create thiamine derivatives in the 1940s, mainly in Japan. Allicin became a model for medicinal chemistry efforts to create other thiamine disulfides. The results included sulbutiamine, fursultiamine (thiamine tetrahydrofurfuryl disulfide) and benfothiamine. These compounds are hydrophobic, easily pass from the intestines to the bloodstream, and are reduced to thiamine by cysteine or glutathione.

(2025). 9781466515574, CRC Press. ISBN 9781466515574

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See also

• Allyl isothiocyanate, the active piquant chemical in mustard plant, , horseradish and wasabi
• syn-Propanethial- S-oxide, the lachrymatory chemical found in
• List of phytochemicals in food

Categories: Thiosulfinates, Anti-inflammatory Agents, Antibiotics, Dietary Antioxidants, Pungent Flavors, Allium, Garlic, Antifungals, Allyl Compounds, Transient Receptor Potential Channel Modulators

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