Allicin
- the smell of health (Molecule of the Month - Jan 2001)
Allicin
- the smell of health Have you ever wondered what causes the smell of garlic? You guessed it, it's allicin! But, I hear you ask, what is allicin? Well, read on and all will become clear!
Allicin (C6H10OS2) is an oily, yellow liquid, which as you will have probably guessed by now, gives garlic its characteristic odour which is due to the SO group. It also has a range of medical properties.
Reactions and synthesis
Allicin is synthesised from alliin (see above) when garlic is crushed or bruised. The reaction is catalysed by an enzyme, alliinase, and as a result quite complex. Allicin is a very reactive compound. It is slightly soluble in water and soluble in alcohol, which is what would be expected of an organic molecule containing OH. It decomposes on heating. In the body, it oxidises the haemoglobin in the blood to methemoglobin.
Being a strongly oxidising compound, it protects garlic from attack by bacteria and insects by disabling the enzymes that are found in the substrate necessary for infections to occur, thus acting as a natural insecticide. It does so by attacking the SH groups found on their active sites. This is also the case for proteinases and alcohol dehydrogenases, enzymes that promote invasion and infection of bacteria in the human body. It is therefore believed that allicin is a good natural cure-all. Studies show that prolonged exposure to this chemical can have such benefits as: lowering incidence of stomach cancer, lenghtening of blood clotting times and reduction of blood lipid levels.
Allicin also belongs to the family of phytochemicals, which are believed to be useful in cancer treatement and cure. Studies are under way to test their effectiveness. Other studies, however appear to show that it is not the allicin but also other chemicals present in garlic which lead to these properties.
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text created by Chris North and Fabio Quadrini of St Peter's college, Oxford. Department of Chemistry, New Laboratory. 2000