Can Refrigerated Food Cause Poisoning? Microbiologist Explains Risk Of Eating Leftovers

It's one of the most common practices worldwide to keep leftover food in the fridge and eat it the next day, or some days later. But not a lot of people know that it can become a health hazard. Primrose Freestone, a microbiologist, has explained the risks of eating certain leftovers. She also revealed how it can be avoided.

"Food poisoning is caused by eating food that has become contaminated with pathogenic bacteria, fungi or viruses," Freestone, a senior lecturer in Clinical Microbiology, University of Leicester, wrote in an article for The Conversation.

When it comes to eating cold leftovers, the key is to handle and store them properly. Cooked food should be refrigerated within two hours of cooking, or one hour if the temperature is above 90 degrees F (32 degrees C). This helps prevent bacterial growth, which can cause food poisoning.

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"Although most people know that food poisoning can be caused by poorly cooked foods or risky food preparation habits, improperly stored leftovers are also a key cause," she wrote.

"It's therefore extremely important you take care when storing leftovers to avoid harming your health."

Some foods are riskier than others, like pizza, cooked rice, pasta, and chicken. These foods can harbour bacteria like Bacillus cereus and Salmonella, which can multiply rapidly at room temperature.

Leftover pizza

When it comes to leftover pizza, she said that it must be refrigerated within two hours of being delivered. It must be stored covered and consumed within two days.

"Surprisingly, the dried herbs and spices that people often sprinkle on their pizzas (such as basil, pepper and oregano) can be susceptible to microbial contamination," Dr Freestone wrote. "This contamination can occur during the harvesting and production phases, or due to improper storage by consumers."

She said that some of these foodborne pathogens that can potentially survive on dried herbs include bacteria that can cause food poisoning.

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Chicken

According to her, raw chicken may be contaminated with the food poisoning germs Campylobacter, Salmonella or Clostridium perfringens. Therefore, all stages of preparing chicken, like washing and cooking, is crucial. "It's also important you only save chicken for leftovers if it has been cooked properly. If there's any trace of blood in the cooked chicken's juices, do not eat it - and certainly don't save it for later," she wrote.

She noted that cooked chicken can be stored for up to three days in the fridge.

Leftover rice and canned food

The expert stated that uncooked rice can contain spores of Bacillus cereus, which is a common food poisoning bacterium. Although it dies due to the heat of cooking, "their spores are heat-resistant and can survive".

"If cooked rice needs to be saved, it should be covered once cooked, cooled quickly, then refrigerated for no more than 24 hours," she said.

When it comes to canned food, it's important to store it safely. "Highly acidic foods, such as canned tomatoes, can be stored refrigerated for five to seven days. Low-acidity canned foods, such as meat, fish, fruit, vegetables and pasta, can only be stored for up to three days," she said.

"Acidic foods last longer because the acid inhibits the growth of food poisoning bacteria."