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To get the most health benefits
from onions, let them sit for five to ten minutes after cutting and
before cooking. Heat will deactivate the thiopropanal sulfoxide and you
want to give it time to fully develop and concentrate before heating.
Onions are a major source of two phytonutrients that play a
significant role in health promotion: flavonoids and the mixture of
over fifty sulfur-containing compounds. The two flavonoid subgroups
found in onions are the anthocyanins that impart a red/purple color to
some varieties, and the flavanols such as quercetin and its derivatives
that are responsible for the yellow flesh and brown skins of many
varieties of onions. The flavonols are concentrated in the skin of most
onions where they contribute to the color of the vegetable.
We
now know that the health promoting compounds in onion, like those in
garlic, are separated by cell walls. Slicing an onion ruptures these
walls and releases the compounds which then combine to form a powerful
new compound: thiopropanal sulfoxide. In addition to mitigating various
diseases, this substance also gives cut onions their pungent aroma and
their ability to make us cry.
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