Garlic has a number of important health benefits that include protection from cardiovascular disease, cancer and infection. However, garlic has a complex chemistry and its biological actions are not fully understood. Despite the numerous health advantages of consuming garlic, many people are deterred because of the pungent taste and aroma that can linger long after it has been consumed. Because of this, garlic supplements have become increasingly popular in recent times, because many are marketed by manufacturers as low odour or tasteless. However, it is known that some of the biologically active chemicals in raw garlic are not present in the manufactured supplements because processing can have detrimental effects on the chemical make up of the final product. The four main supplements available are essential oils, dehydrated powder, oil macerate and extracts.
The main active compound in garlic is allicin. Allicin is formed when garlic is crushed and the enzyme alliinase is release from vacuoles in the cells and acts on the substrate alliin to produce allicin. Allicin then degrades non-enzymatically to form a number of other compounds including 1,2-vinyldithiin, 1,3-vinyldithiin, diallylsulphide (DAS), diallyldisulphide (DADS) and diallyltrisulphide (DATS) and ajoene. The conversion of alliin to allicin is inhibited by pH ≤ 3 (i.e. stomach acid). Dehydrated garlic powder is produced crushing the raw garlic into a fine powder which is them dried. Because the whole cloves of garlic are present in garlic powder, it does retain some of the chemical composition of raw garlic. However, during storage half of the allicin is lost, but it is likely that it degrades to other biologically active products.
Essential oils are obtained by steam distillation of whole garlic. The process involves crushing garlic in heated water and using a solvent (e.g. hexane) to extract the oils, which are placed in a capsule with vegetable oil. Because the solvent only extracts the oils from garlic, the water soluble compounds are completely lost during manufacture. Garlic essential oil is also completely devoid of allicin. The essential oils in garlic consist of mainly diallyl sulphide (DAS), diallyl disulphides (DADS) and diallyl trisulphides (DATS). Garlic essential oils are usually found in capsules with vegetable oil. Oil macerates are condiments for food where whole garlic is ground into vegetable oils. During this process some of the alliin is converted into allicin, but because of its instability much is subsequently lost. However, the decomposition compounds from allicin are present in the oils, including DADS, DAT, DAD, ajonene and dithiins.
Garlic extracts are produced by the soaking of whole garlic cloves in water alcohol solution. After a period of time, the solid garlic material is removed and the solution concentrated, and then sometimes dried. The most popular garlic extract made in this way is called aged garlic extract (AGE) and because of its manufacturing process it contains only the water soluble fractions present in the whole garlic. The most important of these compounds are the water soluble S-allyl mercaptocysteine (SAMC) and S-allyl cysteine (SAC), although a few oil soluble compounds are present. The soaking of AGE can be for as long as 20 months, and during this process many of the compounds with strong odours and tastes are lost. When supplements are being prepared they are generally standardised for SAC, because it is known to be both biologically active and provides health benefits.
RdB
