there has always been a saying in the health care field that overnight vegetables, especially overnight vegetables, can't be eaten in summer, saying that there are a lot of bacteria in overnight vegetables and the nitrite content is high.

is that true? If it exceeds the standard, how serious is it? What about braised pork and braised fish? Are they also out of the standard?

Recently, the reporter went to the laboratory of the Department of Food Science and Nutrition, biosystems engineering College of Food Science, Zhejiang University to measure the nitrite content in overnight vegetables. The reason why only nitrite content is measured is because bacteria in vegetables can be killed by heating overnight, but nitrite cannot be removed by heating.

stir-fry four dishes to see how big the problem is

in order to measure the nitrite content in overnight dishes, the experimenter asked the chef of a well-known middle-and high-end chain restaurant in Hangzhou to cook four dishes: stir-fried vegetables, scrambled eggs with leeks, braised pork and braised crucian carp.

Shi Rui, the head chef of the restaurant, learned that we used it for nitrite experiment and specially selected the freshest ingredients. After the four dishes were cooked, Chef Shi personally packed them and put them into four fresh-keeping boxes.

Chef Shi said that if the leftovers are left for a long time, the nutrients will be lost and bacteria will easily grow. People with bad stomachs are prone to diarrhea, which usually happens a lot, so they usually advise customers to finish the packaged dishes within 2 hours. However, it is not clear whether the nitrite will exceed the standard if the leftovers are left for a long time, said Chef Shi.

The nitrite content in meat is higher than that in vegetables

In order to make people have a more objective understanding of the change of nitrite content in leftovers, the experimenter specially divided four dishes into four parts, put them into disposable degradable lunch boxes, wrapped them with plastic wrap, and labeled them for half an hour, six hours, 18 hours and 24 hours respectively. Then, put these samples into the laboratory refrigerator and refrigerate at 4℃, which is also the temperature set by ordinary household refrigerators.

The experimenter first grinds the dishes into slurry, weighs 1g (note: g grams) of samples, puts them in a conical flask, and dilutes them with distilled water. Let it stand in the dark for 15 minutes, and read the nitrite content directly by the rapid detector. In order to ensure the accuracy of the test results, each sample was tested three times, and finally the average value was taken.

half an hour after cooking, the test results of fried vegetables, scrambled eggs with leeks and braised pork showed that the nitrite content did not exceed the highest limit in China's Limits of Pollutants in Food, that is, vegetables were 4mg/kg and meat was 3mg/kg (note: mg mg, kg kg). However, the nitrite content in braised pork is higher than that in fried eggs with leeks and vegetables. The experimenter said that meat dishes generally add more seasonings than vegetables, and the seasonings themselves contain nitrates, which are converted into nitrite by microorganisms, which leads to higher nitrite content in braised pork.

The nitrite in braised pork exceeded the standard first

Six hours later, it was almost the time interval from lunch to dinner. It is common for many elderly people or dual-income families to eat dishes cooked at noon on rest days and at night.

The experimenter opened the refrigerator, took out the fried vegetables, scrambled eggs with leeks, braised pork and braised crucian carp labeled with "6 hours", then put them in the microwave oven, and heated them for 1 minutes with medium-low heat. After taking them out of the microwave oven, these dishes still looked fresh.

The nitrite content in these dishes was determined by the experimenter. The results showed that after 6 hours, the nitrite content in the leftovers increased, with fried vegetables increased by 16%, leek scrambled eggs increased by 6% and braised pork increased by 71%. Among them, the content of nitrite in braised pork reached 4.2558mg/kg, which exceeded the limit standard of "3mg/kg of meat" in the National Limit Standard for Pollutants in Food.

After being put in the refrigerator for 18 hours, all of them exceeded the standard

18 hours later, the experimenter took out four dishes labeled "18 hours" from the refrigerator and heated them in the microwave oven for testing. The test results showed that the nitrite content in stir-fried vegetables increased greatly, by 44.3% compared with 6 hours, by 54% in braised crucian carp and by 47% in fried eggs with leeks, while the nitrite content in braised meat did not change much.

From this experiment, it can be seen that the nitrite content of fried vegetables, braised pork and braised crucian carp all exceeded the national standard when overnight vegetables were put at noon the next day.

Dishes should not be eaten in the refrigerator for 24 hours

It is almost 24 hours before the four dishes are cooked. After that, the experimenter took out the last batch of four dishes labeled "24 hours" from the refrigerator, and also heated them in the microwave oven for testing.

The results showed that compared with 18 hours, the nitrite content of four dishes continued to increase significantly, and all of them exceeded the limit standard of "Limits of Pollutants in Food". Among them, fried vegetables exceeded the limit by 34%, fried eggs with leeks exceeded the limit by 41%, braised pork exceeded the limit by 84% and braised crucian carp exceeded the limit by 141%.

The experimenter said that the nitrite content in meat dishes exceeded the standard 24 hours after cooking, because the sauces used in braised dishes contained nitrate and the protein content in meat dishes was high. After 24 hours, microorganisms decomposed a large number of protein compounds, which promoted the transformation of nitrate into nitrite.

The nitrite content rises rapidly at room temperature

In order to understand the changes of nitrite content in dishes stored in refrigerator and at room temperature, the experimenter also left a sample of braised crucian carp at room temperature for 4 hours and then determined its nitrite content. The results show that the average value of nitrite content in three tests is 8.9483mg/kg, which is more than double the national limit standard and more than that in the refrigerator for 24 hours. According to Urban Express

The more stale vegetables are, the higher the nitrite content is

Associate Professor Shen Jianfu from the Laboratory of Food Science and Nutrition Department of biosystems engineering College of Food Science, Zhejiang University introduced that the nitrite content of raw vegetables was determined in their laboratory before, and it was found that all vegetables contained nitrite, but it did not exceed the national standard. The general trend is that the more stale vegetables are, the higher the nitrite content is, while those rotten vegetables have more obvious nitrite exceeding the standard.

the reason why vegetables contain nitrite is because nitrogen fertilizer is applied during the growth of vegetables, and nitrate comes from nitrogen fertilizer. Nitrate is not toxic, but microorganisms in the air will enter the leftovers, while microorganisms are more active at room temperature and produce a reductase, which can convert nitrate in dishes into nitrite.

Teacher Shen said that judging from the nitrite content in raw vegetables, the nitrite content in cooked vegetables is only much more. "In theory, the longer the leftovers are left, the more severe the microbial activity and the higher the nitrite content. Moreover, the nitrite content is different for different dishes. "

According to Metropolitan Express

Ingestion of 3g of nitrite

can lead to poisoning and death

Nitrite can oxidize low-iron hemoglobin in blood into methemoglobin, and lose the function of oxygen transport, resulting in tissue hypoxia and even death. Adults ingest 1.2 to 1.5 grams, which can cause poisoning, and 3 grams can cause death. If eaten for a long time, it can also cause diseases such as esophageal cancer, gastric cancer, liver cancer and colorectal cancer.

The Ministry of Health issued an early warning

To prevent nitrite poisoning

Recently, food poisoning accidents occurred frequently in some places, especially nitrite poisoning and food poisoning in collective canteens. The day before yesterday, the Ministry of Health issued an early warning notice on the prevention and control of food poisoning on its official website. The announcement requires that food poisoning caused by nitrite and microbial contamination should be strictly prevented, and the supervision of food production, circulation and catering should be further strengthened.

most of the chemical food poisoning reported in the first half of this year was caused by eating nitrite by mistake, which was common in construction site canteens and small catering businesses. To this end, the management of collective canteens and catering industry should be strengthened, and it is strictly forbidden to buy and use industrial salt to prevent nitrite from being eaten by mistake. Construction sites should strengthen the management of industrial nitrite, and it is strictly forbidden to mix it with other foods and raw materials. Collective canteens and catering industries should use nitrite correctly in strict accordance with the Standards for the Use of Food Additives, and excessive and out-of-range use is strictly prohibited. Food safety supervision departments should strengthen supervision over the production and circulation of nitrite used as food additives.

In addition, summer and autumn are the high season of food poisoning, especially this year, the temperature and humidity in most parts of China are higher than normal, which makes food and its raw materials vulnerable to microbial contamination. Especially when eating seafood such as fish, shrimp, shellfish, etc., beware of food poisoning caused by Vibrio parahaemolyticus, and beware of food poisoning caused by botulinum when eating canned, pickled and fermented foods.

at the same time, the food safety supervision department should strengthen the supervision of food production, circulation and catering to raise public awareness of food safety. The health department should strengthen the monitoring and reporting of food-borne diseases, and find food safety hazards as early as possible.

According to China News Service

Concept water has become carcinogenic water

The AQSIQ recently announced the results of random inspection on the quality of bottled (barrel) drinking water, among which 6 kinds of drinking water were found to contain high concentration of carcinogen "bromate", and the "pure" weak alkaline drinking water produced by well-known enterprises such as Harbin No.6 Pharmaceutical Factory and the "Jingyou" desert high-quality water in Inner Mongolia were on the list, which was shocking.

Ordos jingyou Honghu mineral spring beverage co., ltd. has gained a great reputation in just a few years by playing the "desert brand". This company claims that its products are alkaline "pure natural desert water". However, the General Administration of Quality Supervision, Inspection and Quarantine found that the measured value of bromate detected in a batch of "Jingyou" bottled water was as much as 8 times the standard value. It is reported that bromate has been designated as a "Class 2B" potential carcinogen by the International Agency for Research on Cancer. Zheng Yushan, a senior engineer of the Institute of Product Quality Inspection in Inner Mongolia Autonomous Region, said frankly that at present, most enterprises have limited testing ability for bromate, and they are afraid of increasing costs if they are tested by a third party, which leads to hidden dangers.