alliinase

Alliinase is an enzyme found in Allium species, including garlic and onions, where it catalyzes the rapid conversion of alliin to allicin when plant tissue is damaged. This enzymatic reaction is the biochemical basis for the characteristic garlic aroma and many of its proposed bioactive effects.

In the reaction, alliinase cleaves alliin (S-allyl-L-cysteine sulfoxide) in the presence of water to produce allyl sulfenic acid and dehydroalanine. Two molecules of allyl sulfenic acid spontaneously condense to form allicin, a volatile sulfur-containing compound (diallyl thiosulfinate). Allicin itself is reactive and short-lived, giving rise to a range of secondary sulfur compounds that contribute to flavor and aroma.

Localization and regulation are tied to plant cell organization. Alliinase and alliin are typically segregated within different cellular compartments; wounding or crushing tissues brings them into contact, triggering allicin production as part of a chemical defense response.

Classification and conditions of activity: alliinase is commonly described as a carbon-sulfur lyase that mediates a beta-elimination of the sulfoxide group in alliin. The enzyme shows optimal activity under near-neutral pH and moderate temperatures, and it is readily inactivated by heat or extreme pH.

Applications and relevance: the alliinase–substrate system is of interest in food science for garlic flavor development and in studies of the antimicrobial properties attributed to garlic-derived sulfur compounds. Allicin, the product of alliinase activity, rapidly decomposes into other sulfur-containing compounds, influencing both aroma and potential health effects.