Onion (Allium cepa L.)

Onion certainly is a borderline case between spices and vegetables.

Used plant part
Bulb (subterranean leaves). Superterranean green leaves display the same aroma, but are slightly less intensive; in their culinary use, they equal chives.

Plant family
Alliaceae (onion family).

Sensoric quality
In fresh state, spicy, pungent and lachrymatory.

Main constituents
Fresh onions contain only traces (0.01%) of essential oil, which mostly consists of sulfur compounds: Ethyl and propyl disulfides, vinyl sulfide and other sulfides and thioles. The lachrymatory principle is variously identified as thiopropanal-S-oxide (CH3-CH2-C(SO)H) or its tautomer propenyl sulfenic acid (CH3-CH=CH-SOH). This substance is released from its precursor S-1-propenyl-L-cysteine sulfoxide as a reaction to cell damage; this mechanism is very similar to that in garlic.

Origin
Onion seems to originate from West or Central Asia. In Europe, it is known since the bronze together with garlic, onion it is mentioned in the oldest part of the Bible, the Pentateuch. The Netherlands is the largest producer / origin of Silverskin Onions today.