There is a scare going around that leftover cut onions become poisonous and they attract bacteria and should not be consumed. According to the claim, there is also a risk of food poisoning.
This scare confused me because I have personally used leftover cut onions (both red and yellow) thousands of times in my meals. I have known my mom to use leftover cut onions days later without any problems.
I decided to get scientific evidence to determine whether this scare is real or a hoax. I came across an article that referenced Dr. Joe Schwarcz of McGill University’s Office for Science and Society.
Dr. Schwartz explains:
The fact is that 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.
Schwarcz also notes in his article:
Lastly 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.
And an article on The Chemist’s Kitchen website about the onion’s supposed ability to attract bacteria agrees with Dr Schwarcz’s findings, noting:
Nothing is a bacteria magnet. Firstly, bacteria have minimal mobility. They usually travel in water droplets, if at all. Sneezes, for example. Moulds can release spores which get blown around but bacteria usually grows in moist environments and are slimy, making getting airborne difficult. Secondly, if there was such a thing as a ‘bacteria magnet’ it would be enormously useful in the medical field for drawing bacteria away from the ill and infirmed. Not such use has been made of onions.
Conclusion: Go ahead and use your leftover cut onions as needed without worrying about bacteria or food poisoning.[Source: Hoax-Slayer website]