A Queen’s-led team has discovered the reason why garlic is so good for us.

Kingston - It was widely believed that the organic compound, allicin – which gives the pungent vegetable its aroma and flavour – acts as an antioxidant. But until now it hasn’t been clear how allicin works, or how it stacks up compared to more common antioxidants such as Vitamin E and coenzyme Q10, which stop the damaging effects of radicals.


Queen's Chemistry professor
Derek Pratt has discovered why
garlic is beneficial as a herbal medicine.

Garlic has commonly been used as a natural health product to treat ailments including high cholesterol, and in the prevention of cancer. Queen’s Chemistry professor Derek Pratt and his research team were curious to find the mechanism behind garlic’s potency.

“We didn’t understand how garlic could contain such an efficient antioxidant, since it didn’t have a substantial amount of the types of compounds usually responsible for high antioxidant activity in plants, such as the flavanoids found in green tea or grapes,” says Dr. Pratt, Canada Research Chair in Free Radical Chemistry. “If allicin was indeed responsible for this activity in garlic, we wanted to find out how it worked.”

The research team questioned the ability of allicin to trap damaging radicals so effectively, and considered the possibility that a decomposition product of allicin may instead be responsible. Through experiments with synthetically-produced allicin, they found that sulfenic acid produced when the compound decomposes rapidly reacts with radicals.

“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 it is beneficial,” says Dr. Pratt. “I think we have taken the first step in uncovering a fundamental chemical mechanism which may explain garlic’s medicinal benefits.”

Along with onions, leeks and shallots, garlic is a species in the family Alliaceae. All of these other plants contain a compound that is very similar to allicin, but they do not have the same medicinal properties. Dr. Pratt and his colleagues believe that this is due to a slower rate of decomposition of allicin in the other vegetables, which leads to a lower level of sulfenic acid available to react as antioxidants with radicals.

The Queen’s study was funded by the Natural Sciences and Engineering Research Council of Canada (NSERC) and the Ontario Ministry of Innovation. Other members of the research team are Queen’s Chemistry post-doctoral researcher Vipraja Vaidya and Keith Ingold, from the National Research Council of Canada.