Allicin is the major biologically active component of garlic, But it is not exist in Fresh Garlic.
What?? No,you didn’t misunderstand. The chemistry of garlic is extremely complex. Only when fresh garlic is chopped or crushed, the enzyme alliinase converts alliin into allicin, which is responsible for the “garlic breath“.
Relastionship of Alliin, Alliinase, Allicin,
Allicin is part of a defense mechanism against attacks by pests on the garlic plant.
“allinase” and “alliin”, which are contained in different parts of the garlic plant. This is an unique structure and very efficient weapon because the clove’s defence systems only comes to life (activated) in small location and for a short period of time, whereas the rest of the allinase and alliin remain preserved in their respective compartments and are available for subsequent microbial attacks.
While Allicin generated is unstable and quickly changes into a series of other sulfur-containing compounds such as diallyl disulfide. Allicin could only be kept for a period of time in freezen water solution (Accroding to the reaserch of Professor Erik Block)