Alliin
Also written S-allyl-L-cysteine sulfoxide, S-allylcysteine sulphoxide
Quick answer
The odourless sulphur amino acid that an intact garlic clove or ramsons leaf stores in place of a smell, and that becomes allicin within moments of the tissue being cut.
What it does
Alliin itself has no smell. It is one of the non-volatile S-alk(en)yl-L-cysteine sulphoxides that the intact plant keeps apart from the enzyme alliinase; cutting or crushing brings the two together, and the products — thiosulphinates such as allicin, then sulphides and polysulphides — are the garlic smell. Garlic is characterised by a dominance of alliin. In ramsons, methiin and alliin are usually the two predominant precursors, and the methyl-rich mixture gives a different balance of products from garlic’s.
How it behaves when cooked
Four properties of the molecule, and what they mean at the stove.
- Volatility
- low
- Fat solubility
- low
- Water solubility
- high
- Heat stability
- moderate
Because alliin is only a precursor, what happens to the enzyme decides how much smell it becomes. Extracted garlic alliinase worked fastest at about pH 7 and 35–40 °C, lost activity sharply below pH 5, and fell away rapidly above 40 °C. Those are measurements of the enzyme in buffer, not of a clove in a pan, but they are consistent with the familiar observation that cut garlic left to stand smells stronger than garlic put straight into heat or acid. In ramsons, heating, drying, extraction and storage shift the products from the sharp thiosulphinates of the freshly cut leaf towards sulphides, polysulphides and ajoenes, which is why the cooked or dried leaf smells different from the raw one.
Not present until the plant is damaged
Biosynthesised in the living plant; it is the precursor, not the product + Alliinase acts on it when the tissue is cut
Alliin does not form on damage: it is what damage consumes. The intact clove or leaf holds alliin and alliinase in separate compartments, and cutting, crushing or chewing lets the enzyme turn alliin rapidly into allicin and the related thiosulphinates.
Spices that carry it
Recorded on the compound rather than on each spice, so the two cannot disagree.
- GarlicPrincipal component
The dominant precursor of the clove, and the source of its allicin. Cultivated garlic generally carries more alliin and allicin than ramsons.
- RamsonsMajor component
Present with methiin, which was the more abundant of the two in the fresh-leaf analysis the review reports; that methyl-rich mixture gives ramsons a larger share of methyl-containing thiosulphinates than garlic.
Not to be confused with
Compounds a reader is likely to take for this one, and why they differ.
Allicin
Allicin is what alliin becomes. One is an odourless amino acid stored in the intact plant, the other the sharp, unstable smell of cut garlic, formed from it by the enzyme alliinase.
Questions this page answers
- why does a whole garlic clove not smell
- what is alliin