Can leftover overnight dishes be eaten after all?Does it really cause cancer?
The Spring Festival is a time for families to get together and share delicious food.But often hear people say that there are nitrite in overnight dishes, can cause cancer.Nitrite itself does not have carcinogenicity, but below gastric acid environment, nitrite can react with amine, the decomposition product of protein in the stomach, to generate nitrosamine with strong teratogenicity and carcinogenicity, which is appraised as a carcinogen by the World Health Organization.So are leftovers healthy from a scientific point of view, and is there any harm in eating overnight?Nitrite in uncooked vegetables?Plant food itself contains nitrate and nitrite, plants absorb nitrogen from soil and fertilizer in the process of growth, through a series of biochemical reactions to synthesize amino acids.Nitrate is inevitably produced in this process, and plants also have nitrate reductase, which reduces some of the nitrate to nitrite, but nitrite is usually found in very low amounts.When plants are harvested, more nitrate reductase is released, and during storage, bacteria in the environment also contain nitrate reductase, which greatly increases nitrite levels.The nitrate content of green leafy vegetables is relatively high, so if the vegetables bought are stored for too long, the nitrite will also increase, generally if refrigerated 3-5 days after the nitrite will reach the peak, so for green leafy vegetables or a small number of times to buy, try to eat fresh vegetables.What are the health risks of overnight cooking?The biggest health risk of overnight cooking comes from nitrites.When food is cooked at high temperature, its nitrate reductase activity is lost. However, heated food is also more conducive to bacterial growth. Nitrate reductase in bacteria increases nitrite levels if left at room temperature for a long time, which poses a health risk.Ningbo Quality Inspection Institute once selected 32 kinds of raw materials such as vegetables, meat and eggs common in the market to cook more than 30 kinds of household dishes, and then placed them at room temperature (25℃) and cold storage (4℃) to observe the changes of nitrite and the total number of bacteria after different time.Leaf vegetables experiment found that 12 hours after room temperature, leaf vegetables nitrite content is significantly increased, some more than the “GB2762-2017- Food Safety National standards in food pollutants limit” provisions of pickled vegetables nitrite (to nitrite sodium meter) 20mg/kg of the upper limit, after 24 hours,Some even reached more than 100mg/kg.After 24 hours of refrigeration, the nitrite content of all dishes is still within the safe value.However, after repeated heating, most of the vitamins in vegetables will lose their activity and their nutritional value will be greatly reduced. Therefore, we still develop the good habit of eating as much as possible. Try to eat fresh food, even if refrigerated, do not exceed 24 hours.The nitrite content of fish, meat and soybean products is very low. Some processed cooked meat will use a small amount of nitrite as a food additive to color and inhibit bacteria.Therefore, home-cooked meat dishes are not at risk of rising nitrite overnight, but fish, meat and soy products are protein-rich foods, which are a natural medium for bacterial growth, including many harmful bacteria, which can easily cause gastroenteritis and food poisoning if eaten.Starchy foods such as rice and pasta are easily contaminated by Bacillus cereus when left at room temperature, which can cause symptoms such as abdominal pain, diarrhea and vomiting.As for cold dishes, they have not gone through the process of high-temperature sterilization by cooking, so the bacterial content is relatively high. It is easier to cause food safety risks when stored for a long time. It is recommended to eat them as meals instead of overnight.It is worth noting that overnight dishes are not just dishes that have been left overnight. If they have been left for more than 8-10 hours, they are considered “overnight”.Therefore, if you do have leftovers overnight, always remember to put them in the refrigerator.In addition, the elderly and children generally have weak resistance, or it is not recommended to eat leftovers often.Is overnight food edible or not?The nitrite content of vegetables refrigerated overnight is much lower than the national standard for processed foods, so overnight vegetables can be eaten if properly preserved, and simply saying that overnight vegetables cause cancer is a kind of alarmist.The long-term food safety risk of meat dishes is from harmful microorganisms, and the risk of cancer is very low.How to store overnight dishes?There are many ways we can avoid these food risks in our lives.1. Minimize the shelf life of vegetables, especially leafy greens, and buy them as you eat them.2. Wash and wrap the dishes with plastic wrap in advance to reduce the bacteria carried.3, meat, seafood and other products in the freezer before the best cut into small pieces, eat how much to take, to avoid repeated freeze-thaw, accelerate the deterioration or damage and loss of nutrients.4. For cooked food, if you realize that you can’t finish it in advance, you can refrigerate it before you eat it to reduce bacterial contamination.5, refrigerated overnight food, to ensure that high temperature heat through, that is, heated to 100 degrees Celsius above a few minutes, because most of the harmful microorganisms and toxins are not heat resistant.The World Health Organization once put forward the “five safety points”, which mentioned that cooked food should not be placed at room temperature for more than 2 hours, leftovers should not be heated more than once, and the refrigerator should be cleaned regularly. The refrigerator is not a safe, no matter refrigerated or frozen, food should not be stored for too long.You must bear that in mind!Fu Shufang, master of Food Science and Nutrition Engineering, China Agricultural University, National Key Laboratory of Cardiovascular Disease technician, copyright copyright original author, if there is any copyright copyright, please contact us