A family of three was poisoned after eating leftover salad! Should we stop eating leftover food?

Every summer, "leftover food" becomes a hot topic. For example, recently, "A family of three got poisoned after eating leftover food" and "Can leftover food be eaten?" have been trending on Weibo.

Related topics, picture source: Weibo So, can we eat leftover food? Or in other words, what factors are related to food poisoning?

What is food poisoning?

Food poisoning is poisoning caused by food. In recent years, living conditions have improved, and many people think that food poisoning has disappeared. In fact, according to the monitoring of the Chinese Center for Disease Control and Prevention, in 2017, there were 348 cases of food poisoning in the country, involving 7,389 patients, and 140 people died. Considering that food poisoning occurs mainly from May to September, on average, 50 people are poisoned and 1 person dies every day.

What factors are related to food poisoning?

Food poisoning can be caused by any problem in the purchase, processing and storage of food. Specifically, there are five types of food poisoning: bacterial food poisoning, which is related to bacteria such as E. coli and Salmonella; chemical food poisoning, which is caused by methanol, nitrite, etc.; fungal food poisoning, which is caused by eating poisonous mushrooms; plant food poisoning, such as sprouted potatoes that are not handled properly and green beans that are not thoroughly cooked; and animal food poisoning, which is caused by eating poisonous shellfish and toads.

The causes of food poisoning, picture source: self-made by the author, can be divided into three categories according to their relationship with overnight storage: the first category is completely unrelated and is a problem with the ingredients themselves. Whether eating fresh or stored food, it will cause poisoning; the second category is that the food is contaminated during processing or storage. If it is stored for a long time, the harm may be greater, and various bacterial food poisoning are typical examples; the third category may be related to overnight storage, such as food poisoning caused by nitrite.

Are nitrites in overnight food harmful to the human body?

First, let's take a look at what nitrite is. There are two main types of nitrites we often talk about, one is potassium nitrite and the other is sodium nitrite. Secondly, are they toxic? Yes! The toxicity of nitrite is divided into acute and chronic. Intake of large amounts in a short period of time can cause death (median lethal dose 57mg/kg), and long-term, low-dose intake may accumulate in the human body and cause cell cancer.

What is the so-called low dose?

According to the opinions of experts from various countries, the safe limit is 0.07mg/kg per day. To put it in perspective, a person weighing 50kg would have nothing to worry about if he eats less than 3.5mg a day. Again, where does the nitrite in overnight dishes come from? There are two sources. One is inherent in the vegetables themselves. During the growth process, vegetables absorb ammonia in the soil and produce nitrates and nitrites. Ranked by content, leafy vegetables have the highest content, followed by root vegetables, melons, onions and garlic, cauliflower, nightshades, and beans. Aquatic vegetables have the lowest content. Image source: pexels

In the past, due to the problem of fertilization mode, the nitrite content of domestic vegetables was indeed slightly higher. In recent years, with the promotion of pollution-free vegetables, the nitrite content in vegetables has been greatly reduced.
According to scholars' statistics, the nitrite content of cabbage (leafy vegetables) is about 1.9 mg/kg.

Combined with the above safety limits, as long as you don't eat 1.8 kg a day, you don't have to worry about safety issues. Another thing is that during storage, due to the metabolism of bacteria or vegetables themselves, nitrates gradually turn into nitrites. Conversely, as long as the bacterial activity and the metabolism of vegetables themselves can be inhibited, the nitrite content will not rise rapidly.

The results of the experiment were the same. Ningbo Food Testing Institute conducted an interesting study in which the staff selected 32 common ingredients and prepared 30 dishes according to common methods. Then, they were divided into two groups and stored in 4℃ and 25℃ environments for 6 hours, 12 hours and 24 hours respectively.

The dishes used in the experiment, pictures from the China Internet Joint Rumor Refutation Platform. The results showed that in a 4°C environment, even if the dishes are stored for a whole day (24 hours), the nitrite content is similar to that of fresh dishes, and will not cause nitrite poisoning, and there is no need to worry about excessive nitrite causing cancer; if left at room temperature, after 12 hours, the nitrite content in leafy vegetables will increase significantly, and after 24 hours, it will be enough to reach a harmful dose.

So, after all, the key is to properly handle the ingredients. Let's follow the steps of the ingredients and analyze the risks involved.

The journey of ingredients

The first step is to buy. You may think that buying vegetables is simple. However, nitrite poisoning is mostly caused by accidental ingestion, that is, taking nitrite as table salt. As for poisonous mushrooms and other ingredients, new varieties emerge in an endless stream, and even experts may not be able to guarantee them.

New poisonous mushrooms emerge one after another. Image source: China Centers for Disease Control and Prevention

Therefore, when buying vegetables, on the one hand, try to choose safe ingredients, go to regular places, and buy what you are most sure of; on the other hand, do not buy vegetables that have been stored for too long, and do not buy too much, so as to avoid problems with the ingredients during storage, such as potatoes sprouting.

Step 2: Cleaning

Many people like to rinse meat under the tap to remove blood, which makes it taste better and look cleaner. However, splashing water is likely to bring bacteria on the surface of meat to vegetables or the kitchen. A safer solution is to soak. For leafy vegetables, soaking them in tap water for a while (20 minutes) can also reduce the nitrite content. Another place that many people ignore is hands. After touching meat and vegetables immediately, hands become a springboard for bacteria. Therefore, be sure to wash your hands before and after handling a food.

Image source: pexels

The third step is to have two cutting boards and two knives to handle raw and cooked food respectively. After use, wash them carefully and dry them as soon as possible. The temperature of the processed food should be high enough and the processing time should be long enough to cook the food thoroughly. Fermented rice noodles (such as sour soup) and green beans (also known as kidney beans and kidney beans) are especially worth mentioning.

The former is easily contaminated by bacteria, which can leave toxins in the container and cause food poisoning. The latter, if it naturally contains some lectins, may cause poisoning if it is not cooked well. If you follow the experts' advice and add some water and simmer for more than ten minutes after stir-frying, it will not only not cause poisoning, but also be very nutritious.

Step 4: Store unfinished food in the refrigerator as soon as possible (within 2 hours). It is best to use a shallow container so that the food can cool down as quickly as possible and be fully heated before eating. In addition, the refrigerator can only extend the shelf life of food, but cannot prevent food from spoiling.

Preventing food poisoning, image source: self-made by the author Many people have a set of methods to judge whether food has gone bad, such as looking at the color, smelling the food, tasting it, etc. However, food spoilage may not necessarily show obvious changes in appearance, and relying on sensory judgment is not very reliable. A better way is to clean the refrigerator regularly according to the time recommended by experts.

Food shelf life, data source: foodsafety.gov

It is important to remind you that this timetable is based on the correct use of the refrigerator. If food has been left at room temperature for a long time, or has been contaminated, or even if it is not thoroughly cooked, like the salad we love to eat in summer, then it is safer to throw it away directly.

In short, as long as you follow scientific principles in these four processes, you don’t have to worry about food poisoning.

When cooking, calculate the amount of food and try not to leave any leftovers. This is good for your health and your wallet.

However, if there is leftover, it’s no big deal. As long as you store it properly and heat it up thoroughly when eating, you don’t have to worry about health problems.

References

[1] Zhang Jingyun. Green beans contain toxins, so it’s best not to eat them anymore? Don’t panic, the experiment will tell you the scientific truth - China Internet Joint Rumor Refuting Platform [EB/OL] ([Unknown date]) [2021–07–28]. https://www.piyao.org.cn/2019-03/15/c_1210079399.htm. [2] CDC. 4 Steps to Food Safety [EB/OL] (2019–04–12) [2021–07–28]. https://www.foodsafety.gov/keep-food-safe/4-steps-to-food-safety. [3] Feng Dong. Can we eat “leftover food”? 30 dishes and 450 data reveal the truth - China Internet Joint Rumor Refuting Platform [EB/OL] ([Unknown date]) [2021–07–28]. https://www.piyao.org.cn/2020-09/10/c_1210792437.htm. [4] Hu Ping, Yu Shaowen, Huang Qilan, et al. Analysis of nitrite food poisoning in major provinces and cities in China from 1988 to 2003 [J]. Journal of Shenzhen University, 2005(01): 57–69. [5] Ruan Guangfeng. Correctly understand nitrite and scientifically handle leftovers [N]. China Pharmaceutical News, 2021: 004. [6] Tan Guoxin, Luo Zongming, Cui Yingde. Changes in nitrite content during storage of fresh vegetables [J]. Food Industry Science and Technology, 2003(04): 74-75+87.[7]Cao Xiaoqian, Sun Tao, Parhat, et al. Effects of different treatment conditions on nitrite content in leafy vegetables[J]. Chinese Food and Nutrition, 2018, 24(02): 33–36.[8]Wang Xiaoye, Ren Jinghuan, Wang Zhe, et al. Analysis of epidemiological characteristics of food poisoning incidents in China in 2017[J]. Disease Surveillance, 2018, 33(05): 359–364.[9]Ma Yan, Wang Xiaoye, Ding Fan, et al. Analysis of epidemiological characteristics of nitrite food poisoning incidents in China from 2005 to 2014[J]. Chinese Rural Health Care Management, 2018, 38(09): 1174–1176.

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Reviewer: Wang Guizhen, National Nutritionist

Tadpole Musical Notation original article/reprinted with source editor/heart and paper