Does eating leftover rice and vegetables cause cancer? Can we still eat them? One article explains

Author | Xue Qingxin, registered nutritionist, registered nutrition technician, first batch of nutrition instructors of the National Health Commission, health manager, public nutritionist

Review | Liu Zhengxin, Deputy Director of the Department of Gastroenterology, Beijing Chaoyang Hospital, Capital Medical University

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During the Chinese New Year, people naturally enjoy a feast. In order to satisfy the appetites of all family members, every household usually prepares a large table full of delicious food. However, after a meal, there are often many dishes left over. Therefore, leftovers are inevitable on the first, second, and third day of the Chinese New Year.

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There are many news reports about food safety problems caused by eating leftover food. The safety of leftovers is of great concern to many people. There is a rumor that "leftovers contain high levels of nitrite, which can easily cause cancer." What is going on? How can we preserve leftovers without wasting them and ensure food safety? This is something worth paying attention to.

analyze

Can eating leftovers cause cancer?

Rumor has it that leftovers contain high levels of nitrite, which can cause cancer if eaten.

In fact, nitrite is not only found in leftovers. Vegetables themselves contain nitrite. The nitrite content of fresh vegetables is about 1 mg/kg. The worse the storage conditions, the higher the nitrite content.

Although cooked vegetables also contain nitrite, the cooking process can reduce the nitrite content. The nitrite content of vegetables will decrease after being fried or boiled, and the nitrite content of boiled vegetables is lower than that of fried vegetables. The nitrite content of leftover overnight vegetables will indeed increase slightly, but eating them will not cause cancer.

In most cases, the nitrite content of overnight dishes is not high. Someone randomly selected three different cooked dishes from the cafeteria, including cabbage, carrots and beef, and tested their nitrite content after 12 hours, 24 hours and 48 hours. The test results are shown in the table below:

According to national standards, the residual nitrite content in vegetable products should not be higher than 4 mg/kg. From the test results of this experiment, it can be seen that the nitrite content of the three dishes sampled and tested was within the safe range and did not exceed the standard when refrigerated at 4°C in three time periods.

Therefore, as long as overnight dishes are properly stored at 4°C under refrigerated conditions, the nitrite content will still be within the acceptable safety range for the human body within 2 days, and there is no need to worry about causing cancer after eating them. However, attention should be paid to hygiene during storage, because contamination by microorganisms and bacteria will greatly increase the nitrite content.

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Which leftovers are safe to eat?

Although under normal circumstances, properly stored leftovers can be eaten safely, it is not recommended to eat leftover cold dishes compared to cooked hot dishes.

Because cold dishes are not cooked at high temperatures, the bacteria in the food are not completely killed and are easily contaminated by other bacteria, which may cause food poisoning, diarrhea, vomiting and other uncomfortable symptoms; and bacteria reproduce quickly, and the increase in the number of bacteria will also increase the nitrite content in the dishes.

Therefore, it is best to make a small amount of cold dishes at a time and eat them on the same day. As for cooked dishes, as long as they are stored in a refrigerated condition at 4°C for less than two days, they can be eaten safely if they are fully heated before eating.

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How to store leftovers scientifically?

Different types of leftovers have slightly different storage requirements.

· Vegetables: It is best to eat all the vegetables in a dish, especially green leafy vegetables. If they are left over the next day, not only will the taste deteriorate, the nutritional value will decrease, the color will also darken, and you will lose your appetite. If you really can't finish it, you can seal it with plastic wrap and refrigerate it, and eat it all the next day.

· Meat: During holidays, meat dishes account for a large proportion of the meals on many families’ tables, so it is inevitable that some meat will be left over. Meat is easy to breed bacteria. If there is a small amount left, you can seal it and put it in the refrigerator. It needs to be fully heated before the next meal. If there is a large amount left, it is recommended to package it and freeze it.
· Eggs: Scrambled or boiled eggs can be directly sealed and refrigerated and eaten within 3 days. However, it is best not to leave soft-boiled eggs overnight. After all, soft-boiled eggs are not fully cooked and sterilized, and are more likely to become a "breeding ground" for bacteria. For safety reasons, they should be eaten on the same day.

· Soup: Any leftover soup can be boiled again to sterilize it, poured into a larger porcelain bowl, sealed with plastic wrap, and stored in the refrigerator. It needs to be boiled again before the next drink.

· Soy products: If you can’t finish stir-fried dried tofu, fried tofu, or fried bean curd sheets, reduce the turning and seal them in the refrigerator. Heat them up before eating next time.

· Rice: There are many people at family gatherings. In order to avoid not having enough food, a lot of rice will be cooked at one time, and there will inevitably be leftovers. Rice is easy to breed Bacillus at room temperature. The leftover rice must be refrigerated in a sealed box in time, and it is best to eat it within 4 days. You can heat it up directly next time you eat it, or use it to make fried rice. It should be noted that you should try to reduce the number of times you heat the rice, otherwise not only will the rice lose more nutrients, but it will also be bad for blood sugar control.

In addition, different dishes must be stored separately to avoid mixing of flavors and affecting the taste next time you eat them.

Should leftovers be put in the refrigerator after they cool down?

Although most leftovers can be eaten safely, if there are leftovers that cannot be finished, they must be stored in the refrigerator in time. Many people are used to waiting for the leftovers to cool down at room temperature before putting them in the refrigerator, which is incorrect.

Because 4~60℃ is a dangerous temperature range, bacteria can easily grow and reproduce. When the temperature exceeds 60℃, most bacteria cannot survive; below 4℃, the reproduction rate of most bacteria can be reduced, which is relatively safe.

Dietary Guidelines for Chinese Residents 2022 Edition

If leftovers are left to cool naturally at room temperature for a long time, it will provide favorable conditions for the proliferation of bacteria, which is not conducive to the preservation of leftovers. Therefore, if there are leftovers that cannot be eaten, be sure to reduce turning them over, put them in a clean sealed box, cover them with a lid, and store them in the refrigerator. This will quickly reduce the temperature of the dishes and create negative pressure in the sealed box, reducing the risk of spoilage.

The refrigerator is not a safe, you can't put everything in it

In addition to leftovers that need to be put in the refrigerator, many families also stock up on New Year's goods. In order to facilitate storage, they almost stuff them all into the refrigerator. This practice is wrong and is not conducive to the preservation of certain foods.

Tropical fruits such as bananas, lychees, dragon fruits, and mangoes are not suitable for being kept in the refrigerator, as they are prone to frostbite. Potatoes and sweet potatoes are also not suitable for being kept in the refrigerator, just keep them in a cool and dry place. Leafy vegetables, mushrooms, and fresh beans can be stored in the refrigerator.

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However, there are three tips to keep in mind when storing vegetables in the refrigerator:

① Do not wash them. Washed vegetables have a high water content, which can easily breed bacteria and is not conducive to storage.

② Don’t wrap the vegetables with plastic wrap. Vegetables also need to breathe. If the plastic wrap is not breathable, it will accelerate the deterioration of vegetables. If you are afraid of dirtying the refrigerator, you can poke a few holes in the plastic wrap. It would be even better if you have a breathable box with holes.

③ Do not store all vegetables together. Many vegetables will release ethylene, which will ripen other vegetables and reduce their shelf life. It is best to store different vegetables separately.

In addition, do not fill the refrigerator too full, as this will affect the refrigeration effect and be detrimental to food preservation.

Chart: Homemade

in conclusion

During the Spring Festival, every household will prepare a rich meal. Try to make less, store it properly, and avoid waste. Even if there are leftovers, try to eat them within 2 days. If they are not stored properly and go bad, don't eat them!

Editor-in-charge｜Liu Yantong (internship)

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