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Alliin
and Allicin, two important organosulfur compounds from Garlic (Allium sativum)
For further information, see Garlic
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Alliin, the
major sulfur compound of whole, unbruised Garlic |
Allicin,
produced from Alliin by enzyme action when Garlic is crushed |
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| Alliin
(S-allylcysteine sulfoxide), is constructed of an allyl
group (green), a sulfoxide group (yellow), and the amino acid cysteine
(purple
- in its regular form, contains –SH rather than S=O).
Alliin is biosynthesized from its parent
compound, S-Allylcysteine (deoxyalliin). It is by far the most abundant
of the four cysteine sulfoxides known to be present in whole, unbruised
Garlic and in properly dried powders. Whole Garlic contains from 6 to 14
milligrams of alliin per
gram, fresh weight, and from 18 to 42 mg/g dry weight (a typical
fresh Garlic clove weighs 2 - 4 g, and so would contain 12 - 56 mg of
alliin; it also contains about 65% water, hence
the higher concentration of alliin in dry
Garlic).1 Analyses of Garlic powder tablets have revealed a
wide range of alliin concentrations: from a low
of 0.4 up to 24 mg per gram of tablet. "Allicin-standardized"
tablets contain an average of 13 mg/g of alliin, while non-standardized
tablets contain, on average, 7 mg/g. To
preserve the maximum amount of alliin in dried
products, the cloves should be minimally sliced and carefully freeze-dried.
Too much slicing mixes more alliin and alliinase,
resulting in increased allicin production prior to
dehydration; the unstable allicin soon
degrades. Additionally, excess heat during dehydration inactivates the
alliinase, destroying the allicin-yield
potential of the product. After the powdering process, the remaining
alliin and alliinase are quite stable as long
as the powder is kept dry and reasonably cool. The average five-year storage loss of
allicin-yield is 36%.2
Alliin is quite stable in the absence of active
alliinase, and can also be found in cooked Garlic (if it has not been
converted to allicin before cooking), Garlic vinegars, and aged extracts.
Alliin has demonstrated
antioxidant activity in some studies,3,4 but not in others.5,6
Its parent compound, S-allylcysteine, is a proven antioxidant, as is its
derivative, allicin.
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Allicin
(Diallyl thiosulfinate), is constructed from two allyl groups (green), and a
thiosulfinate group (yellow). It is biosynthesized from two molecules of
alliin (or from its close relative, methiin -
methylcysteine sulfoxide) by the enzyme alliinase. Allicin makes up about
60-90% of the total thiosulfinates in crushed Garlic.
The total allicin-yield has been calculated as
2.5 - 5.1 mg/g of fresh, crushed Garlic or about 5 to 20 mg per clove.7
For dried Garlic powder tablets, allicin-yield
is determined by subjecting the product to simulated gastrointestinal
conditions, including agitation in simulated stomach acid (pH 1.5) followed
by agitation in simulated intestinal fluid (pH 7.5). One respected brand of
enteric-coated supplement claims to release 3.2 mg of
allicin per 350 mg Garlic powder, or 9.1 mg/g of product. This falls
within the range of the natural allicin
potential in one clove of Garlic.
Once formed, allicin is
unstable; pure allicin at room temperature has
a half-life of 2-16 hours; in garlic juice or crushed garlic, 2.4 days;
in garlic juice diluted 1:10 in water, 22 days.8 Refrigeration
increases the life of allicin by a factor of
twenty.9 This indicates
that while allicin is not stable enough for
commercial use, its medicinal properties can be taken advantage of in home
herbal preparations.
Allicin has a low
solubility in water, around 2%. In air or water, it degrades to sulfides
including diallyl disulfide, diallyl trisulfide, and allyl methyl
trisulfide. Steam distillation (to make Garlic oil) produces these and at
least twenty other sulfides. In oil macerates (such as Garlic minced in
olive oil), allicin transforms to sulfides, ajoene, and vinyldithiins. These
compounds are physiologically active as well; in many cases, allicin itself
is not directly responsible for medicinal effects, but its transformation
products are. Synergistic effects are likely.
For more information on the transformation products
of allicin and the γ-Glutamylcysteines
(including S-allylcysteine), go to the Advanced page.
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Toxicology
In 1980, a clinical study was performed
in which 200 people ingested 15 grams of raw Garlic daily for 3 1/2 weeks.
No side effects were noted.10 Another study in 1991, with 50
participants ingesting 10 grams daily for 8 weeks, also noted no side
effects.11 Several smaller studies have recorded similar results.
There is one case recorded of a person
who regularly ingested four cloves of raw Garlic daily and suffered platelet
dysfunction and spinal epidural hematoma.12 Surgeons often
recommend cessation of Garlic or Garlic supplement consumption prior to
surgery, in order to decrease blood clotting times.
Chronic exposure to raw (i.e., among
food industry workers) Garlic or Garlic juice has resulted in
allicin-initiated allergic
contact eczema. There have been a few cases of allergic asthma reported in
workers exposed to Garlic dust and powders.
Purified allicin
is strongly hepatotoxic to rats in large, long-term doses (equivalent to the
amount in 1750 g of raw Garlic).13 Many other animal studies have
demonstrated hepatotoxicity with ingestion of excessive amounts of Garlic
and Onions.
Various blood cell (leukocytes and
erythrocytes) changes have been observed in animals given very large amounts of
Garlic or Garlic extracts; including anemias, reduced phagocytic activity,
and hemolysis.
It has been noted that, in patients
taking the blood thinner warfarin, intake of Garlic supplements can lead to
significantly increased blood clotting times.14 Some of this
potentially dangerous drug interaction effect may be due to allicin
or its transformation products.
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References
1. Lawson, L. D. Garlic: A
Review of Its Medicinal Effects and Indicated Active Compounds. In:
Phytomedicines of Europe: Chemistry and Biological Activity, ACS Symposium
Series #691. Lawson,
L. D.; Bauer, R. Eds. American Chemical Society: Washington DC, 1998; pp
176-209.
2. Lawson, L. D. In: Garlic: the Science and Therapeutic Application of
Allium sativum L. and Related Species; Koch, H. P.; Lawson, L. D. Eds.
Williams & Wilkins: Baltimore, 1996; pp 37-107.
3. Rabinkov et al., Biochim Biophys Acta 1998. Feb 2; 1379(2):
233-234.
4. Kourounakis, P. N., Rekka, E. A. Res Commun Chem Pathol Pharmacol
1991. Nov; 74(2): 249-52.
5. Siegers, C. P. et al., Phytomedicine 1999. Mar; 6(1): 13-6.
6. Hirata, R., Matusushita, S. Biosci Biotechnol Biochem 1996. Mar;
60(3): 484-5.
7. Lawson, 1998.
8. Lawson, 1998.
9. Lawson, 1996.
10. Sucur, M. Diabetol Croat 1980. 9: 323-338.
11. Gadkari, J. V., Joshi, V. D. J Postgrad Med 1991 37:
128-131.
12. Rose, K. D., et al. Neurosurgery 1990 26: 880-882.
13. Augusti, K. T., Matthew, P. T. Experientia 1975 31:
148-149. Chem Abst 83 (1975) 484.
14. Sunter, W. H. Pharm J. 1991 246: 722. |
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