Garlic has been studied extensively for its health benefits. Already inancient time, people ate garlic to control intestinal disorders, worms, flatulence, wounds and ageing. The health benefits of garlic are attributed to many phytochemicals which may act synergistically. Industrial preparations may contain different proportions of these phytochemicals. The best known garlic phytochemical is the thiosulfinate allicin. However, allicin is not very stable and will be absent in most preparations.
There are four types of garlic preparations on the market: dried garlic powder, aged garlic extract, garlic oil and garlic oil macerate. Aged garlic extract is obtained by macerating sliced garlic in water or diluted alcohol. The extract is the aged for a period up to 20 months. During this ageing period the sulphur components are converted into stable compounds. Aged garlic extract contains mainly water soluble phytochemicals such as S-allylcysteine. Garlic and garlic preparations have many claimed effects: reduction of risk of cancer and heart disease, stimulation of the immune system, detoxification and general tonic. A study by TH Abdullah and colleagues entitled "Enhancement of natural killer cell activity in AIDS with garlic" (J. Oncol. 1989, 21:52-53) showed that 1.8 g of aged garlic extract enhanced the human immune system.
The health benefits of garlic extracts could be attributed to phytochemicals, which are produced during the extraction process, such as S-allylcysteine, S-allylmercaptocysteine, N-alfa-fructosyl arginine. Aged garlic extract has antioxidant properties whereas raw garlic acts as oxidant. Many studies have shown that garlic has cholesterol-lowering properties, whereas other studies did not show such effect. This discrepancy may be explained partly by the difference in composition of garlic preparations.
The main phytochemicals in garlic are alliin, methiin and S-allylcysteine. When garlic is damaged or crushed the sulphur components are transformed in different organosulfur compounds. Enzymes in garlic will convert alliin into allicin, which has antimicrobial action. Allicin is not very stable, so it will have no biological effect when ingested by humans. Even when large quantities are consumed no allicin is detectable either in the serum or urine.
S-allylcysteine on the other hand is bioavailable and has the ability to lower cholesterol, act as an antioxidant, inhibit the cancer process and protect the liver from toxins. S-allylcysteine is present in aged garlic extract and has been well researched. The safety of aged garlic extract has been confirmed by many studies.
Source: Amagase H, Petesch BL, Matsuura H, Kasuga S and Itakura Y. Intake of Garlic and its Bioactive Components. Journal of Nutrition, 2001 March, 131(3s):955S-62S