alliin

“Chemists say that when garlic is crushed, chopped, or chewed, an enzyme is released that converts one of garlic's key sulfur compounds, called alliin, into allicin.”

Health Fact: Garlic Wards Off Many Health Threats

“When you cut a clove of raw garlic, a neutral vegetable substance called alliin mixes with a plant enzyme called allinase to produce the potent allicin factor.”

Simon & Schuster: The Tao of Health, Sex and Longevity

“According to the boffins, garlic has no flavour until the cell walls are broken, and when the cell walls are broken, the enzyme alliinase is released, which reacts with a precursor compound, alliin, to form diallyl thiosulfinate and other thiosulfinates the pongy and tasty side of the garlic.”

The Guardian: Food for Fort: Talking turkey, and other matters

“Kyolic is the only manufacturer of aged garlic, which is a much more effective and scientifically-backed form of garlic than formulas which contain just "allicin" or "alliin" for example.”

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