Alliin. Computer model of a molecule of alliin (S-allylcysteine sulphoxide, C6. H11. N. O3. S), an odourless garlic compound. Atoms are colour-coded: carbon is dark blue; nitrogen, light blue; sulphur, yellow; oxygen, red; hydrogen, white. Alliin is a chemically modified form of the amino acid cysteine. When garlic is crushed or cut, it is converted by the enzyme alliinase to allicin, which is the main component of garlic's strong odour. Allicin is thought to have therapeutic effects including antibacterial, antioxidant and cholesterol-reducing properties.