News - Canned shelf life is long due to preservatives?

China Consumer Daily reported (reporter Li Jian) Open the lid (bag), it is ready to eat, tastes good, and is easy to store. In recent times, canned food has become a must-have item in many households’ stocking lists. However, a recent online micro-survey of more than 200 consumers by a reporter from China Consumer News showed that due to concerns that the food is not fresh, must have too many preservatives added, and lost too much nutrition, most people have a comprehensive view of canned food. “Favorability” is actually not too high. But are these doubts really justified? Hear what experts in food science have to say.

Soft cans, have you heard of it?

In the era of relative scarcity of materials, canned food used to be a different flavor full of “luxury”. In many memories of the post-70s and post-80s, canned food is a nutritional product that can only be eaten during festivals or illnesses.

Canned food was once a delicacy on the monotonous table of ordinary people. Almost any food can be canned. It is said that the selection of canned food is diverse, which can make people feel the richness of a full-fledged Manchurian feast.

However, if your perception of canned food is still at the level of fruits, vegetables, fish and meat packaged in tin cans or glass bottles, it may be a bit “outdated”.

“National Food Safety Standard for Canned Food” clearly defines canned food as a commercial non-standard food made from fruits, vegetables, edible fungi, livestock and poultry meat, aquatic animals, etc., which are processed through pretreatment, canning, sealing, heat sterilization and other processes. Canned food with bacteria.

Associate Professor Wu Xiaomeng from the School of Food Science and Nutritional Engineering of China Agricultural University explained in an interview with a reporter from China Consumer News that the meaning of canned food is first to be sealed, and the second is to achieve commercial sterility. The packaging it uses can be either rigid packaging represented by traditional metal cans or glass cans, or flexible packaging such as aluminum foil bags and high-temperature cooking bags, which are generally referred to as soft canned foods. For example, vegetable bags in aluminum foil bags in various self-heating foods, or prefabricated normal temperature cooking bags such as Sichuan-flavored pork slices and fish-flavored pork shreds, all belong to the category of canned food.

Around 2000, as the earliest industrialized category in the food industry, canned food was gradually labeled as “unhealthy”.

In 2003, a list of the “Top Ten Junk Foods Published by WHO” (canned food is listed) was widely considered to be the fuse for the coldness of canned food in the people. Although this list has been fully falsified, canned food, especially the traditional “hard canned food” (packaged in metal or glass jars), seems to be difficult to open the password of the Chinese people.

Data shows that although my country’s canned food production ranks first in the world, the per capita consumption of canned food is less than 8 kilograms, and many people consume less than two boxes per year.

Eating canned food is about equal to eating preservatives? This micro-survey shows that 69.68% of the respondents rarely buy canned food, and 21.72% of the respondents only buy it occasionally. At the same time, although 57.92% of the respondents believe that canned food is easy to store and suitable for stocking at home, 32.58% of the respondents still believe that canned food has a long shelf life and must have too many preservatives.

In fact, canned food is one of the few foods that requires no or minimal preservatives.

The “National Food Safety Standard for the Use of Food Additives” stipulates that in addition to canned bayberry (propionic acid and its sodium and calcium salts are allowed to be added, the maximum use amount is 50 g/kg), canned bamboo shoots, sauerkraut, edible fungi and nuts (allowed to add Sulfur dioxide, the maximum use amount is 0.5 g/kg), canned meat (nitrite is allowed, the maximum use amount is 0.15 g/kg), these 6 types of canned food require very low doses of preservatives to deal with specific microorganisms, and the rest cannot be added. preservative.

So, what is the “frozen age” of canned food that is often kept for 1 to 3 years or even longer at room temperature?

Wu Xiaomeng told the “China Consumer News” reporter that canned food is actually protected by two means of sterilization technology and sealed storage. In most cases, food spoilage is affected by microorganisms such as bacteria and molds. Processing canned food through sterilization methods such as high temperature and high pressure can cause a large number of these microorganisms to die. At the same time, processes such as exhaust and sealing can greatly reduce food pollution. The oxygen content in the container stagnates the growth of some potential microorganisms in the container, and blocks the passage of oxygen or microorganisms outside the container into the container, ensuring the safety of food. With the development of food processing technology, new technologies such as controlled atmosphere sterilization and microwave sterilization have shorter heating time, lower energy consumption, and more efficient sterilization.

Therefore, it is not necessary to worry about too many preservatives in canned products. The “popular science” on the Internet that “eating canned food is about equal to eating preservatives” is completely alarmist.

Is canned food stale and nutritious?

The survey found that in addition to worrying about preservatives, 24.43% of the respondents believed that canned food was not fresh. Among the more than 150 respondents who “seldom buy” and “never buy” canned food, 77.62% of the respondents believe that canned food is not fresh.

Although some consumers have begun to consider choosing canned food that is easier to preserve due to factors such as epidemic prevention and control and stockpiling at home, this has not changed people’s perception of its “staleness”.

In fact, the emergence of canned processing technology itself is to keep food fresh.

Wu Xiaomeng explained that food such as meat and fish will quickly spoil if not processed in time. If vegetables and fruits are not processed in time after being picked, nutrients will continue to be lost. Therefore, some brands with a relatively complete supply chain generally choose the mature period with the largest production of ingredients and make them fresh, and the entire material selection and processing process even takes less than 10 hours. There is no more nutrient loss than the route fresh ingredients take from picking, transport, sale, and then to the consumer’s refrigerator.

Of course, some vitamins with low heat tolerance do lose their heat during canning, but most nutrients are retained. This loss is also no more than the loss of nutrients from everyday home-cooked vegetables.

Sometimes, canned foods may be beneficial for vitamin retention. For example, canned tomatoes, although sterilized, most of the vitamin C content is still there when they leave the factory, and they are relatively stable. Another example is canned fish. After high temperature and high pressure sterilization, not only the meat and bones of the fish are softer, but also a large amount of calcium is dissolved. The calcium content of a box of canned fish can even be 10 times higher than that of fresh fish of the same weight. Iron, zinc, iodine, selenium and other minerals in fish will not be lost.

Why can’t “fat” canned food

In most cases, it is recommended that consumers go to large shopping malls or supermarkets to buy products from regular manufacturers, and judge the quality of canned food from the aspects of appearance, packaging, sensory quality, labeling, and branding.

Wu Xiaomeng reminded that the cans of normal metal cans should have a complete shape, no deformation, no damage, no rust spots, and the bottom cover should be concave inward; the center of the metal cover of glass bottle cans should be slightly depressed, and the contents should be viewed through the bottle body. The shape should be complete, the soup is clear, and there are no impurities.

A special reminder is that if you encounter the following conditions, no matter how tempting the contents of the can, do not eat it.

One is canned “fat listening”, that is, the expansion tank. The main reason for the expansion of the can is that the inside of the can is contaminated by microorganisms and generates gas. These gases accumulate to a certain extent, which will lead to the deformation of the can. Therefore, canned food is “gaining weight”, a very clear red flag that it has gone bad.

Second, the canned packaging is leaking and moldy. In the process of storage and transportation of canned products, due to bumps and other reasons, the product packaging will be deformed, and air leaks at the seal of the can lid. The air leakage causes the products in the can to come into contact with the outside world, and microorganisms may take advantage of the opportunity to enter.

The survey found that 93.21% of the respondents had the right choice for this. However, about 7% of the respondents believed that the bumps caused during transportation were not a big problem, and chose to buy and eat.

Wu Xiaomeng reminded that most canned meats and fruits and vegetables are not very heavy, and it is recommended to eat them at one time after opening. If you can’t finish it, you should pour it into an enamel, ceramic or plastic food container, seal it with plastic wrap, store it in the refrigerator, and eat it as soon as possible.

As for canned sugar sauce and jam, the sugar content is generally 40%-65%. Relatively speaking, it is not easy to deteriorate after opening, but it should not be careless. If you can’t eat it all at once, you should cover the jar, or pour it into another container and seal it with plastic wrap, then store it in the refrigerator, and try to eat it within two or three days. In autumn and winter, it can be stored for a few more days.