Thursday, April 19, 2012

Leftover Onions Are Poisonous?

There are claims that leftover onions are poisonous because they are "magnets for bacteria." There are also claims that "leaving onions around a room can absorb the flu virus along with bacteria that cause other illnesses thereby preventing people from becoming sick".

So, onions are magnets for bacteria. That doesn't make sense. Magnets? For just bacteria? Just bad bacteria? How does that work? Even if bacteria, just bad bacteria, could somehow travel to an onion, I'd think the sulfur compounds would do them in.

Looks like Dr. Joe Schwarcz of McGill University Office for Science and Society wondered the same thing.1
"The terminology that onions are "bacterial magnets" makes no sense. No food attracts bacteria, although of course some are more likely to support bacterial multiplication once infected."
"Onions are not especially prone to bacterial contamination. In fact, quite the opposite. Onions feature a variety of sulphur compounds that have antibacterial activity. Furthermore, cutting an onion triggers the release of enzymes that initiate a chemical reaction producing propenesulfenic acid, which in turn decomposes to yield sulphuric acid. It is the sulphuric acid that makes you cry by irritating the eyes! But sulphuric acid also inhibits the growth of bacteria. Also, a cut onion's surface dries out quickly, reducing the moisture that is needed for bacteria to multiply."
He gives these reasons for consuming onions:
"That’s because onions contain a variety of compounds that have health benefits. Fructo-oligosaccharides, for example, stimulate the growth of bifidobacteria which suppress the growth of potentially harmful bacteria in the colon. Eating onions has also been linked with a reduced risk of stomach cancer and flavonoids in onions can lower blood pressure and reduce the risk of blood clots forming. Some studies have even shown improved lung function in asthmatics who consume lots of onions."
This Dr. Joe is an interesting person. I wish he had a blog.
1Is It True That Onions Are “Magnets For Bacteria?”
Photo of an onion I had leftover in the refrigerator.


Leo said...

That's preposterous! I usually cut up an onion on Sunday night,throw it in a baggie, and use it throughout the week.

When we do Indian tacos, chopped onions sit out all day as people come and go to make their tacos.

I love onions. ;) peace

Bix said...

Leo, what do you put on your tacos? And what kind of shell do you use?

Bix said...

Preposterous is a great word.

To be honest, I think the belief that onions absorb bad bacteria and protect from sickness comes from a placebo effect.

Likewise, I think the belief that leftover onions can make you sick is a nocebo effect.

Although, I know there really are compounds in onions that affect people. You can see where the belief effects came from.

Angela and Melinda said...

We do the same thing w/ onions, only we chop an onion in half, use a half on bean burritos, and store the other half in a baggie in the fridge. I too LOVE onions!

Anonymous said...

People believe babies are born to virgins, the world is 6000 years old and onions are magnets. People will believe anything.

Anonymous said...

Try this out guys & come back to reComment on your Results.

PLACE SOME LEFT OVER ONIONS (cut in halfs) around your kitchen & outside ...from afternoon till overnight. I'll let you see yourself what you discover.

Note. Dont forget to come back and post what your discover. Hint: worms

Ronald said...

OMG! Spontaneous generation!

Anonymous said...

I love onions I've eaten sliced onions by them selves on bread andbutter ive saved onions for days in the frig and never gotten sick