Alliin

Alliin is the common name for S-allyl-L-cysteine sulfoxide, a sulfur-containing compound found in garlic and other Allium species. It is a non-protein amino acid derivative that serves as a storage form of sulfur in the plant. Alliin is water-soluble and is present in relatively high amounts in fresh garlic cloves.

In intact plant tissue, alliin and the enzyme alliinase are stored in separate cellular compartments. When the tissue is damaged, such as during crushing or chopping, alliinase is released and catalyzes the conversion of alliin to allicin (diallyl thiosulfinate) through a sequence that generates allyl sulfenic acids which subsequently condense to form allicin. Allicin is volatile and unstable, rapidly decomposing into a variety of sulfur-containing compounds that contribute to the characteristic aroma of garlic.

Alliin levels vary with garlic cultivar, maturity, growing conditions, and post-harvest handling. Processing methods influence the formation of allicin: crushing inactivates or preserves different steps, while heating can denature alliinase and reduce allicin formation. In aged garlic products, enzymatic activity is largely inactivated, and different sulfur compounds, such as S-allyl-L-cysteine (SAC), may predominate.

Health discussions around alliin focus largely on its role as a precursor to bioactive sulfur compounds like allicin. While allicin and related degradation products have been studied for antimicrobial, anti-inflammatory, and cardiovascular effects, evidence in humans is mixed and not yet conclusive. Alliin itself is typically discussed as part of garlic’s broader sulfur chemistry rather than as an isolated therapeutic agent.

See also: allicin, allium, garlic.