Can we eat leftover melon, tea and vegetables? This article explains it all!

In life, we often see such news:

"Eating overnight food can cause cancer," "Eating overnight watermelon can cause acute gastroenteritis," "A family of three ate overnight black fungus and were admitted to the hospital that night."...

Many people will feel a little scared when seeing this kind of news. So can we eat overnight food? How to preserve the leftover food? Today, let's talk about some issues about overnight drinks and food that everyone is concerned about.

Can I drink overnight tea?

There is no strict definition of overnight tea, which mainly refers to tea that has been brewed for too long. Usually, the water temperature for brewing tea is between 90 and 100 degrees Celsius, which will kill common bacteria, and some substances in the tea leaves themselves have certain antibacterial effects. If tea is left open indoors, a small amount of bacteria from the air will enter, but the bacteria in the tea grow very slowly, and the impact caused is minimal.

In addition, tea that has been brewed for too long will not produce any toxic substances except that its color will darken and its taste will be bitter. The reason why the color darkens is due to the oxidation of tea polyphenols. So you can drink tea that has been brewed for a long time, but if it is too bitter, there is no need to drink it.

Image source: pxhere

Can I eat overnight meals?

Whether leftovers are safe or not does not depend on whether they are left overnight or how long they are stored, but whether the food produces harmful substances or deteriorates during storage. There are two major safety issues with leftover food: one is the proliferation of microorganisms, which can cause food deterioration; the other is the increase in nitrites, which can cause food poisoning and have the risk of cancer.

However, the increase of nitrite in overnight food is not as terrible as people think. Experiments have shown that if green leafy vegetables such as spinach are not turned over after cooking and placed in a refrigerator at 4°C, the nitrite content will rise from about 3 mg/kg to 7 mg/kg after 24 hours. Generally speaking, the human body will have adverse reactions if it ingests 200 mg of nitrite at one time. According to this dosage, if you eat nearly 30 kg of overnight spinach at one time, you may break your stomach before you get poisoned.

So it’s not that you can’t eat leftover food, but everyone should also be careful and it’s best to only leave meat and not vegetables, and don’t leave any cold dishes.

In addition, when storing leftovers in the refrigerator, remember to seal them with plastic wrap or a fresh-keeping bag and place them on the upper layer of the refrigerator, separate from the unwashed fruits and vegetables on the lower layer. After taking out the refrigerated leftovers, they must be fully heated before eating. Of course, if conditions permit, it is best to cook a small amount each time and eat it immediately, and not eat leftovers.

Can you eat overnight watermelon?

In the summer, if you buy a big watermelon and cannot finish it, even if you put it in the refrigerator after cutting it, many people are worried that the total number of colonies on the cut surface of the watermelon will exceed the standard.

However, the study showed that there was no significant difference in the total number of colonies of the same variety of watermelon in the fresh cut surface, the cut surface after overnight refrigeration, and the samples 2 cm below the surface of the cut surface after overnight refrigeration. This shows that low-temperature refrigeration can significantly delay or inhibit the growth of bacteria on the cut surface of watermelon, and there is no problem of food safety caused by excessive total number of colonies on overnight watermelons.

Although overnight watermelon is not fatal, if you want to eat it with more peace of mind, it is best to clean the knife, watermelon, hands, and cutting board before cutting the watermelon, and be careful to use the knife and cutting board for cutting cooked food. If you can't finish the watermelon, you should also wrap it with plastic wrap before refrigerating it.

Image source: pxhere

Don’t eat these overnight foods!

Although many foods are left over overnight, it is not as terrible as you think.

However, if overnight food is not stored properly, it is likely to breed bacteria. If some people with weak immunity, such as children, pregnant women and the elderly, eat it, it may cause food poisoning, such as soaked black fungus, white fungus, fermented rice flour and starch products.

Soaked black fungus, white fungus, fermented rice flour, and starch products are easily contaminated by Pseudomonas cocovenenans, which produces thermostable fumonisin toxins at room temperature. The toxins enter the human body and cause abdominal pain, bloating, diarrhea, nausea, vomiting and other symptoms. Excessive intake can also lead to multiple organ failure and even death. Soak black fungus and white fungus in cold water for 1 to 2 hours before processing and consumption. The soaking time should not exceed 4 hours, and the time should be shorter if soaked in hot water. If mucus or odor is produced, it is best to throw it away.

Image source: Wikipedia

Food preservation tips

In people's daily understanding, the fresher the food, the better. However, leftovers are inevitable in life, which forces us to leave these foods "overnight", so we need to master some tips on preservation:

1. Unfinished food should not be stored at room temperature for more than 2 hours.

2. It is best to separate leftovers. If you put a large amount of food in a large container, the food will take a long time to cool, and the risk of bacteria growth will increase. So it is best to divide the food into several portions and put them in shallow containers to speed up the heat dissipation of the food.

3. Keep cooked food and raw food strictly separate. Because refrigerator space is limited, many people put raw food such as fresh vegetables directly next to cooked food, which can easily cause cross-infection of bacteria. Cooked food should not be stored in the refrigerator for more than 3 days. If you suspect that the food has spoiled, discard it as soon as possible.

4. Food stored at a temperature of 0~4℃ should be heated to at least 75℃ before eating after being taken out of the refrigerator. Food with high water content must be cooked to boiling point.

Image source: pxhere

In fact, when we cook, we always prepare a lot of food for fear that there will not be enough, but these foods have to be refrigerated if we can’t finish them. But the next day, we don’t want to eat them so we delay eating them until the third or fourth day, or we throw them away because we haven’t eaten them for a long time.

Therefore, in order to avoid food waste, we should also develop the habit of hoarding less ready-made food. After eating a cooked meal, you can not only feel full, but also get spiritual pleasure. Encourage yourself that today is another day to eat as much as you cook and gain a sense of satisfaction!

References

[1] Does overnight tea cause cancer? [J] Health and wellness community

[2] Lü Xin, Chen Lihua, Li Xiaolin, et al. Evaluation of food safety of fresh-cut watermelon after overnight refrigeration [J]. Journal of Fujian Agricultural Sciences, 2018, 33(8): 865-869.

Author: Xu Lang, popular science creator

Review | Han Hongwei, Director of Risk Communication Department, National Food Safety Risk Assessment Center