The antioxidant effects are due to a compound called sulfenic acid, which is produced by the decomposition of allicin, according to data published in the international edition of Angewandte Chemie.
"Basically the allicin compound has to decompose in order to generate a potent antioxidant," said lead author Dr Derek Pratt. "The reaction between the sulfenic acid and radicals is as fast as it can get, limited only by the time it takes for the two molecules to come into contact. No one has ever seen compounds, natural or synthetic, react this quickly as antioxidants."
Consumer awareness of the health benefits of garlic, mostly in terms of cardiovascular and immune system health, has benefited the supplements industry, particularly since consumers seek the benefits of garlic without the odours that accompany the fresh bulb.
Garlic supplements are worth more than $100m (€79.5m) in the US and are also one of the biggest sellers in the UK market.
However, allicin is not found in fresh garlic, and is only formed when garlic is crushed. Furthermore, there are question marks over how much allicin, if any, many of the supplements on the market do contain. Some products have taken the stance of emphasising the allicin content of their products.
"While garlic has been used as a herbal medicine for centuries and there are many garlic supplements on the market, until now there has been no convincing explanation as to why garlic is beneficial," explained Dr Pratt. "I think we have taken the first step in uncovering a fundamental chemical mechanism which may explain garlic's medicinal benefits."
Using a synthetically-produced allicin, the researchers found that an acid produced when the compound decomposes rapidly reacts with radicals.
Specifically, they report that garlic’s ability to trap potentially damaging peroxyl-radicals is due primarily to 2-propenesulfenic acid formed by the decomposition of allicin.
Pratt also commented on the potential of other Allium spp., like onions, leeks and shallots, to act as potential antioxidants. All of these other plants contain a compound that is very similar to allicin, but the properties are not the same. This could be due to a slower rate of decomposition of the allicin analogs in the other plans, which leads to a lower level of sulfenic acid available to react as antioxidants with radicals, said Pratt.
The study was funded by the Natural Sciences and Engineering Research Council of Canada (NSERC) and the Ontario Ministry of Innovation.
Source: Angewandte Chemie International EditionVolume 48, Issue 1, Pages: 157-160“Garlic: Source of the Ultimate Antioxidants - Sulfenic Acids”Authors: V. Vaidya, K.U. Ingold, D.A. Pratt
“While this is a very nice bit of chemical work, it is not relevant to the nutritional use of garlic. The very high reactivity of propenesufenic acid limits its lifetime, and neither this compound, nor its precursor (and product), allicin, can be found in the bloodstream after garlic consumption.
"While the ability of garlic supplements to generate allicin is clearly important, this generation is presumed to occur in the gut, and rapidly give rise to the more readily recognized organosulfur compounds that can be found in the bloodstream. It is highly unlikely that propenesulfenic acid directly participates in the any antioxidant benefits of garlic consumption.”
- Todd D. Porter, PhDAssociate Professor, Pharmaceutical SciencesCollege of Pharmacy, University of Kentucky