Allicin is an organosulfur compound obtained from
garlicAllium sativum, commonly known as garlic, is a species in the onion family Alliaceae. Its close relatives include the onion, shallot, leek, and chive. Garlic has been used throughout recorded history for both culinary and medicinal purposes. It has a characteristic pungent, spicy flavor that...
. It is also obtainable from onions, and other species in the family
AlliaceaeAlliaceae is a family of herbaceous perennial flowering plants. They are monocots, part of order Asparagales. The family has been widely but not universally recognised; in the past, the plants involved were often treated as belonging to the family Liliaceae, and still are by some botanists.The APG...
. It was first isolated and studied in the laboratory by Chester J. Cavallito in 1944. This colourless liquid has a distinctively pungent smell. This compound exhibits antibacterial and anti-fungal properties. Allicin is garlic's defence mechanism against attacks by pests.
Allicin is an organosulfur compound obtained from
garlicAllium sativum, commonly known as garlic, is a species in the onion family Alliaceae. Its close relatives include the onion, shallot, leek, and chive. Garlic has been used throughout recorded history for both culinary and medicinal purposes. It has a characteristic pungent, spicy flavor that...
. It is also obtainable from onions, and other species in the family
AlliaceaeAlliaceae is a family of herbaceous perennial flowering plants. They are monocots, part of order Asparagales. The family has been widely but not universally recognised; in the past, the plants involved were often treated as belonging to the family Liliaceae, and still are by some botanists.The APG...
. It was first isolated and studied in the laboratory by Chester J. Cavallito in 1944. This colourless liquid has a distinctively pungent smell. This compound exhibits antibacterial and anti-fungal properties. Allicin is garlic's defence mechanism against attacks by pests.
Structure and occurrence
Allicin features the
thiosulfinateIn organosulfur chemistry, thiosulfinate is a functional group consisting of the linkage R-S-S-R . The thiosulfinate functional group is rare, but these compounds are invoked as intermediates in the oxidation of thiols to sulfonic acids, which is a common transformation. They feature a S center...
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
alliinaseAlliinases are a class of enzymes found in plants of the genus Allium, such as garlic and onions. Alliinase is responsible for catalyzing chemical reactions that produce the volatile chemicals that give these foods their flavors, odors, and tear-inducing properties. Alliinases are part of the...
on
alliinAlliin is a sulfoxide that is a natural constituent of fresh garlic. It is a derivative of the amino acid cysteine. When fresh garlic is chopped or crushed, the enzyme alliinase converts alliin into allicin which is primarily responsible for the aroma of fresh garlic...
. Allicin is chiral and occurs naturally as only a single
enantiomerIn stereochemistry, an enantiomer is one of two stereoisomers that are mirror images of each other that are "non-superposable" , much as one's left and right hands are "the same" but opposite....
. The racemic form can be generated by oxidation of diallyl
disulfideIn chemistry, a disulfide usually refers to the structural unit composed of a linked pair of sulfur atoms. Disulfide usually refer to a chemical compound that contains a disulfide bond, such as diphenyl disulfide, C
6H
5S-SC
6H
5.-Inorganic vs. organic...
:
2 +
RCO3Hmeta-Chloroperoxybenzoic acid is a peroxycarboxylic acid used widely as an oxidant in organic synthesis. mCPBA is often preferred to other peroxy acids because of its relative ease of handling...
→ CH
2=CHCH
2S(O)SCH
2CH=CH
2 + RCO
2H
Alliinase is irreversibly deactivated below a pH of 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 23C.
Potential health benefits
Several animal studies published between 1995 and 2005 indicate that allicin may: reduce
atherosclerosisAtherosclerosis is the condition in which an artery wall thickens as the result of a build-up of fatty materials such as cholesterol...
and fat deposition., normalize the
lipoproteinA lipoprotein is a biochemical assembly that contains both proteins and lipids. The lipids or their derivatives may be covalently or non-covalently bound to the proteins. Many enzymes, transporters, structural proteins, antigens, adhesins and toxins are lipoproteins...
balance, decrease
blood pressureBlood pressure is the pressure exerted by circulating blood on the walls of blood vessels, and is one of the principal vital signs. During each heartbeat, BP varies between a maximum and a minimum pressure...
, have anti-
thromboticThrombosis is the formation of a blood clot inside a blood vessel, obstructing the flow of blood through the circulatory system. When a blood vessel is injured, the body uses platelets and fibrin to form a blood clot, because the first step in repairing it is to prevent loss of blood...
and anti-
inflammatoryInflammation is the complex biological response of vascular tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. Inflammation is a protective attempt by the organism to remove the injurious stimuli as well as initiate the healing process for the tissue. Inflammation is not a...
activities, and function as an
antioxidantAn antioxidant is a molecule capable of slowing or preventing the oxidation of other molecules. Oxidation is a chemical reaction that transfers electrons from a substance to an oxidizing agent. Oxidation reactions can produce free radicals, which start chain reactions that damage cells...
to some extent . Other studies have shown a strong oxidative effect in the gut that can damage intestinal cells.
In 2009, Vaidya, Ingold, and Pratt have clarified exactly how allicin works to produce its medicinal effects, such as trapping damaging
radicalsIn chemistry, radicals are atoms, molecules, or ions with unpaired electrons on an otherwise open shell configuration. These unpaired electrons are usually highly reactive, so radicals are likely to take part in chemical reactions...
. According to them, it is the
sulfenic acidA sulfenic acid is an organosulfur compound and oxoacid with the general formula RSOH, where R ≠ H. Sulfenic acids are generally unstable. An example of a sulfenic acid is benzenesulfenic acid, PhSOH....
s, which are produced by the decomposition of allicin, that extremely rapidly react with
free radicalThe free-radical theory of aging states that organisms age because cells accumulate free radical damage over time. A free radical is any atom or molecule that has a single unpaired electron in an outer shell. While a few free radicals such as melanin are not chemically reactive, most...
s, and bind with them. "We suggest that the peroxyl-radical-trapping activity of garlic is primarily due to 2-propenesulfenic acid formed by the decomposition of allicin."
The antibacterial activity
The antibacterial activity of allicin was reviewed by Ankri and Mirelman in 1999. Due to the increasing prevalence of
methicillinMeticillin or methicillin is a narrow spectrum beta-lactam antibiotic of the penicillin class. It was developed by Beecham in 1959...
-resistant
Staphylococcus aureusStaphylococcus aureus is the most common cause of staph infections. It is a spherical bacterium, frequently part of the skin flora found in the nose and on skin. About 20% of the population are long-term carriers of S. aureus. S...
(MRSA) in hospitals and the community, there has been an urgent need for new agents that could be used to deal with these bacteria. In this connection, in 2004, Cutler and Wilson have studied the effect of allicin on these bacteria. They used a new stable, aqueous extract of allicin, and have achieved very promising results.
Cutler and Wilson note that the use of a water-based extract of allicin stabilises the allicin molecule. They note further that this may be due to the hydrogen bonding of water to the reactive oxygen atom in allicin; also, there may be water-soluble components in crushed garlic that destabilise the molecule. (Presumably, the dilution of these components in water helps to preserve the allicin molecule.)
Cutler and Wilson tested allicin on 30 clinical isolates of MRSA that show a range of susceptibilities to
mupirocinMupirocin is an antibiotic originally isolated from Pseudomonas fluorescens NCIMB 10586, developed by Beecham.
...
. Strains were tested using
agar diffusion testThe agar diffusion test, or the Kirby-Bauer disk-diffusion method, is a means of measuring the effect of an antimicrobial agent against bacteria grown in culture....
s. Of the strains tested, 88% had
minimum inhibitory concentrationMinimum inhibitory concentration , in microbiology, is the lowest concentration of an antimicrobial that will inhibit the visible growth of a microorganism after overnight incubation...
s for allicin liquids of 16 µg/mL, and all strains were inhibited at 32 µg/mL. Furthermore, 88% of clinical isolates had
minimum bactericidal concentrationThe Minimum Bactericidal Concentration is the lowest concentration of antibiotic required to kill an organism. . Not as commonly seen as the Minimum inhibitory concentration . It can be determined from broth dilution MIC tests by subculturing to agar media without antibiotics. Antimicrobials are...
s of 128 µg/mL, and all were killed at 256 µg/mL. Of these strains, 82% showed intermediate or full resistance to mupirocin.
Also, Cutler and Wilson found that an
aqueous creamAqueous Cream BP is a light, paraffin-based emulsion which is officially registered in the British Pharmacopoeia and categorised by the British National Formulary as a non-proprietary emollient preparation...
of allicin was somewhat less effective than allicin liquid. At 500 µg/mL, however, the cream was still active against all the organisms tested—which compares well with the 20,000 µg/mL mupirocin currently used for topical application.
See also
- Allistatin
Allistatin is an antibiotic found naturally in plants of the Allium group, which includes garlic and onions.It is recognized as being a strong broad-spectrum fungicide and antibiotic against numerous serious microorganisms...
, a natural antibiotic found in garlic and onions.
- Allyl isothiocyanate
Allyl isothiocyanate is the organosulfur compound with the formula CH2CHCH2NCS. This colorless oil is responsible for the pungent taste of mustard, horseradish, and wasabi...
, the active piquant chemical in mustardMustards are several plant species in the genera Brassica and Sinapis whose small mustard seeds are used as a spice and, by grinding and mixing them with water, vinegar or other liquids, are turned into the condiment known as mustard...
, radishThe radish is an edible root vegetable of the Brassicaceae family that was domesticated in Europe in pre-Roman times. They are grown and consumed throughout the world. Radishes have numerous varieties, varying in size, color and duration of required cultivation time...
es, horseradishHorseradish is a perennial plant of the Brassicaceae family, which also includes mustard, wasabi, broccoli, and cabbages. The plant is probably native to southeastern Europe and western Asia, but is popular around the world today...
and wasabiWasabi is a member of the Brassicaceae family, which includes cabbages, horseradish and mustard. Known as "Japanese horseradish", its root is used as a spice and has an extremely strong flavour...
- Capsaicin
Capsaicin is the active component of chili peppers, which are plants belonging to the genus Capsicum...
, the active piquant chemical in chile peppers
- Piperine
Piperine is the alkaloid responsible for the pungency of black pepper and long pepper, along with chavicine . It has also been used in some forms of traditional medicine and as an insecticide. Piperine forms monoclinic needles, is slightly soluble in water and more so in alcohol, ether or...
, the active piquant chemical in black pepperBlack pepper is a flowering vine in the family Piperaceae, cultivated for its fruit, which is usually dried and used as a spice and seasoning. The fruit, known as a peppercorn when dried, is a small drupe approximately five millimetres in diameter, dark red when fully mature, containing a single...
- Syn-propanethial-S-oxide
Syn-propanethial-S-oxide is a volatile gas that has lachrymator effects . As onions are sliced, cells are broken, allowing enzymes called alliinases to break down amino acid sulfoxides and generate sulfenic acids . Sulfenic acids are unstable and spontaneously rearrange into syn-propanethial-S-oxide...
, the chemical found in onionOnion is a term used for many plants in the genus Allium. They are known by the common name "onion" but, used without qualifiers, it usually refers to Allium cepa. Allium cepa is also known as the "garden onion" or "bulb" onion...
s
- List of phytochemicals in food
External links