Flavor compounds of Allium

Allium is a large and diverse genus of about 500 species. Unlike other crop species, the Alliums, which include onion, garlic, leek, shallot, chives, rely on sulfur for their unique flavor. The major flavor of Alliums results from the activity of the enzyme, alliinase, acting on certain sulfur-containing compounds when tissues are broken or crushed.

Sulfur is the primary element in many compounds that produce a specific flavor profile to a specific species of Allium.

The volatile flavor compounds in onions are mainly propyl disulfide and methyl propyl disulfide. Allicine and its analogue are not stable in air. They gradually decompose to produce disulfide or trisulfide compounds, which are the major flavor compounds found in Allium plants.

Each spice belonging to an Allium plant can be characterized by the kind of major sulfide compound contained in it. Sulfur and carbonyl compounds are two major categories of the volatiles observed in Allium plants.

There are three main R-group to be considered for the flavor compounds of Allium plant:
*Methyl group (CH3-)
*Propyl group (CH3CH2CH2-)
*Allyl group (CH2=CH.CH2-)

Compounds with a propenyl group (CH3CH=CH-) are also found in onion. Differences in smell or flavor among garlic, onion, leek, and others are due to the ratio of these groups.
Flavor compounds of Allium