The power of foods:Onion(たまねぎ) Part 1

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Sep 8, 2010 20:31
A onion is a vegetable which is eaten in many countries.
It's said that people who built pyramid ate onions in ancient Egypt.
Onions have a long history.
Today's topic is onions.

(I will write in three journals because this is a long journal.
The informations I write here are on the internet, so I'm sorry if there are some wrong informations.)

When we cut onions, our eyes are irritated and caused to water.
This is because the allyl sulfide(※), which generated from sulfur amino acid contained abundantly in onion by an enzyme, is evaporated and stimulate the mucous membrane of the eyes.
Eye irritation can be avoided by chilling or heating onions before cutting, cutting onions under the fan, or using a sharp blade to cut onions.
These ways work because the causative compound is volatile, soluble in water, and weak against heat.

※For details, it is a little incorrect.
The sulfenic acid is generated by an enzyme called alliinase from iso allyl cystein sulfoxide(isoalliin) contained in onions.
The sulfenic acid is an active and unstable compound, and it soon polymerize to form thiosulfinate, and it transforms into various sulfur compounds, one of which cause the pungent taste.

The thiopropanethial S-oxide, which is generated from sulfenic acid by an enzyme called LFS(lachrymatory factor synthase), is called LF(lachrymatory factor), and this is the actual eye irritation causative compound.
The enzyme called LFS was discovered by the researchers from House Foods which is Japanese food company.
They succeeded to make onions which don't cause eye irritation by gene modification to inhibit the gene expression of this enzyme.

As I explained above, The efficacy of onions is often explained as the effects of allyl sulfide, but the efficacy seems to be the combination of the effects of the allyl sulfide analogs, so I call them sulfur compounds as a collective term.

To be continued...

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