Garlic contains a wealth of sulfur compounds; most important for the taste is allicin (diallyl disulphide oxide), which is produced enzymatically from alliin (S-2-propenyl-L-cysteine sulfoxide) if cells are damaged; its biological function is to repel herbivorous animals. Allicin is deactivated to diallyl disulphide; therefore, minced garlic changes its aroma if not used immediately. In the essential oil from steam distillation, diallyl disulphide (60%) is found besides diallyl trisulphide (20%), diallyl sulfide, ajoene and minor amounts of other di- and polysulphides. Sulfur compounds of this kind are typical for the onion family; see also bear’s garlic, onion and chives.
In other botanical groups, garlic scent caused by similar sulphur chemism is uncommon. While the cabbage family is rich in species accumulating sulphur compounds (e. g., they cause the typical flavour of cress, mustard and the various cabbage types), true garlic aroma is rarely found; an example for such a plant is hedge garlic (Alliaria petiolata). Asafetida is an important sulphur-containing spice that replaces garlic is some South Asian cuisines. Lastly, the exotic garlic vine (Cydista aequinoctialis syn. Mansoa alliacea) should be mentioned: This South American creeper boasts of beautiful flowers and strikingly garlic-scented Leaves.