Allicin is anorganosulfur compound obtained fromgarlic andleeks.[1] When fresh garlic is chopped or crushed, the enzymealliinase convertsalliin into allicin, which is responsible for the aroma of fresh garlic.[2] Allicin is unstable and quickly changes into a series of other sulfur-containing compounds such asdiallyl disulfide.[3] Allicin is anantifeedant, i.e. the defense mechanism against attacks by pests on the garlic plant.[4]
Allicin is an oily, slightly yellow liquid that gives garlic its distinctive odor. It is athioester of asulfinic acid. It is also known as allyl thiosulfinate.[5] Its biological activity can be attributed to both its antioxidant activity and its reaction withthiol-containing proteins.[6]
Allicin features thethiosulfinate functional group, R-S-(O)-S-R. The compound is not present in garlic unless tissue damage occurs,[1] and is formed by the action of the enzymealliinase onalliin.[1] Allicin ischiral but occurs naturally only as aracemate.[7] Theracemic form can also be generated by oxidation ofdiallyl disulfide:[8][9]
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.[10][11] Furthermore, allicin can be unstable, breaking down within 16 hours at 23 °C.[12]
The biosynthesis of allicin commences with the conversion of cysteine intoS-allyl-L-cysteine. Oxidation of this thioether gives the sulfoxide (alliin). The enzymealliinase, which containspyridoxal phosphate (PLP), cleaves alliin, generating allylsulfenic acid (CH2=CHCH2SOH),pyruvate, andammonium ions.[6] At room temperature, two molecules of allylsulfenic acid condense to form allicin.[5][9]
Allicin has been studied for its potential to treat various kinds ofmultiple drug resistance bacterial infections, as well as viral and fungal infectionsin vitro, but as of 2016, the safety and efficacy of allicin to treat infections in people was unclear.[13]
A Cochrane review found there to be insufficient clinical evidence regarding the effects of allicin in preventing or treatingcommon cold.[14]
It was first isolated and studied in the laboratory byChester J. Cavallito and John Hays Bailey in 1944.[15][7] Allicin was discovered as part of efforts to createthiamine derivatives in the 1940s, mainly in Japan. Allicin became a model formedicinal chemistry efforts to create other thiamine disulfides. The results includedsulbutiamine,fursultiamine (thiamine tetrahydrofurfuryl disulfide) andbenfothiamine. These compounds are hydrophobic, easily pass from the intestines to the bloodstream, and are reduced to thiamine by cysteine orglutathione.[16]: 302
^Kourounakis PN, Rekka EA (November 1991). "Effect on active oxygen species of alliin and Allium sativum (garlic) powder".Research Communications in Chemical Pathology and Pharmacology.74 (2):249–52.PMID1667340.
^abNikolic V, Stankovic M, Nikolic L, Cvetkovic D (January 2004). "Mechanism and kinetics of synthesis of allicin".Die Pharmazie.59 (1):10–4.PMID14964414.
^abRabinkov A, Miron T, Konstantinovski L, Wilchek M, Mirelman D, Weiner L (February 1998). "The mode of action of allicin: trapping of radicals and interaction with thiol containing proteins".Biochimica et Biophysica Acta (BBA) - General Subjects.1379 (2):233–44.doi:10.1016/s0304-4165(97)00104-9.PMID9528659.
^abBlock E (2010).Garlic and Other Alliums: The Lore and the Science. Cambridge: Royal Society of Chemistry.ISBN978-0-85404-190-9.
^Cremlyn RJ (1996).An introduction to organosulfur chemistry. Wiley.ISBN0-471-95512-4.
^Hahn G (1996). Koch HP, Lawson LD (eds.).Garlic: the science and therapeutic application ofAllium sativum L and related species (2nd ed.). Baltimore: Williams and Wilkins. pp. 1–24.ISBN978-0-683-18147-0.
^Marchese A, Barbieri R, Sanches-Silva A, Daglia M, Nabavi SF, Jafari NJ, Izadi M, Ajami M, Nabavi SM (2016). "Antifungal and antibacterial activities of allicin: A review".Trends in Food Science and Technology.52:49–56.doi:10.1016/j.tifs.2016.03.010.
^Cavallito CJ, Bailey JH (1944). "Allicin, the Antibacterial Principle of Allium sativum. I. Isolation, Physical Properties and Antibacterial Action".Journal of the American Chemical Society.66 (11): 1950.Bibcode:1944JAChS..66.1950C.doi:10.1021/ja01239a048.
^Bettendorff L (2014). "Chapter 7 - Thiamine". In Zempleni J, Suttie JW, Gregory JF, Stover PJ (eds.).Handbook of vitamins (Fifth ed.). Hoboken: CRC Press. pp. 267–324.ISBN978-1-4665-1557-4.
