The long shelf life of canned food depends entirely on preservatives？

Food safety consumption tips

The long shelf life of canned food depends entirely on preservatives?

Open the lid (bag) to eat, delicious, convenient storage, recently, canned food has become a must-have item in many families’ inventory. However, an online micro-survey conducted by the reporter of China Consumer News recently on more than 200 consumers shows that most people’s comprehensive "goodwill" towards canned food is actually not too high because of the doubts that the food is not fresh, too many preservatives must be added, and too many nutrients are lost. But do these doubts really make sense? Let’s listen to experts in the field of food science.

Respondents’ cognition of canned food

Have you ever heard of soft cans?

In the era of relative scarcity of materials, canned food used to be a different flavor full of "luxury". In many memories of post-70s and post-80s, canned food is a nutritional product that can only be eaten on holidays or when you are sick.

Canned food was once a fancy food on the monotonous table of ordinary people. Almost all food can be canned. It is said that the selection of canned food is diverse, which can make people feel the richness of Manchu-Han banquet.

However, if your knowledge of canned food remains at the level of fruits, vegetables, fish and meat packed in tin cans or glass bottles, it may be a bit "outdated".

The National Standard for Food Safety "Canned Food" clearly defines canned food as a commercial aseptic canned food which is made of fruits, vegetables, edible fungi, livestock and poultry meat, aquatic animals, etc. as raw materials and processed by pretreatment, canning, sealing and heating sterilization.

Wu Xiaomeng, an associate professor at the College of Food Science and Nutritional Engineering of China Agricultural University, explained in an interview with the reporter of China Consumer News that the first meaning of canned food is sealing, and the second is to achieve commercial sterility. Its packaging can be either hard packaging represented by traditional metal cans or glass cans, or flexible packaging such as aluminum foil bags and high-temperature retort pouch, which is generally called soft canned food. For example, aluminum foil bagged vegetable bags in all kinds of self-heating foods, or prefabricated normal-temperature cooking bags such as Sichuan-flavored pork slices and fish-flavored shredded pork, 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, an online list of "Top Ten Junk Foods Published by WHO" (canned food is on the list) was generally regarded as the fuse of canned food being cold among the people. Although this list has been fully falsified, it seems that it is difficult to open the tongue code of Chinese people, especially the traditional "hard cans" (metal or glass cans).

The data shows that although China’s canned food production ranks among the top in the world, the per capita consumption of canned food is less than 8 kilograms, and many people even consume less than two boxes a year.

Respondents’ purchase of canned food

Eating canned food is about the same as eating preservatives?

This micro-survey shows that 69.68% of the respondents rarely buy canned food, and 21.72% 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 hoarding 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 without preservatives or with the least amount of preservatives.

According to the National Food Safety Standard for the Use of Food Additives, except canned bayberry (propionic acid and its sodium salt and calcium salt are allowed to be added, the maximum dosage is 50g/kg), canned bamboo shoots, pickled vegetables, edible fungi and nuts (sulfur dioxide is allowed to be added, the maximum dosage is 0.5g/kg) and canned meat (nitrite is allowed to be added, the maximum dosage is 0.15g/kg), which requires very low dosage.

Then, cans that can be kept for 1 to 3 years or even longer at room temperature can be kept fresh by "frozen age".

Wu Xiaomeng told the reporter of China Consumer News that canned food actually protects food safety through sterilization technology and sealed storage. In most cases, food spoilage is caused by bacteria, molds and other microorganisms. Processing canned food by sterilization means such as high temperature and high pressure can kill a large number of these microorganisms. At the same time, processes such as venting and sealing can greatly reduce the oxygen content in food and containers, make some potential microorganisms in the containers grow stagnant, and block the passage of oxygen or microorganisms outside the containers into the containers, thus ensuring food safety. With the development of food processing technology, new technologies such as modified atmosphere sterilization and microwave sterilization have shorter heating time, lower energy consumption and more efficient sterilization.

Therefore, it is unnecessary to worry about too many preservatives in canned products. The "popular science" on the Internet that "eating canned food is about eating preservatives" is completely alarmist.

Canned food is not fresh and nutritious?

The survey found that among the respondents who "never bought" canned food, 52.94% thought canned food was not fresh.

Although some consumers began to consider choosing canned food that is easier to preserve because of epidemic prevention and control, hoarding goods at home and other factors, this did not change people’s understanding of its "stale".

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

Wu Xiaomeng explained that foods such as meat and fish will rot quickly if they cannot be processed in time. If vegetables and fruits are not processed in time after picking, the nutrition will be lost continuously. Therefore, some brands with a relatively complete supply chain generally choose to adopt and make the ingredients at the mature stage with the largest output, and the whole material selection and processing process even takes less than 10 hours. Compared with the route of fresh ingredients from picking, transporting and selling to consumers’ refrigerators, there is no more nutritional loss.

Of course, some vitamins with low heat resistance will be lost in the process of canned food processing, but most nutrients will be preserved. Compared with the loss of nutrients caused by daily household processing and cooking vegetables, this loss is not more.

Sometimes, canned food may be beneficial to the maintenance of vitamins. For example, although canned tomatoes have been sterilized, most of the vitamin C content is still there when they leave the factory, and it is relatively stable. Another example is canned fish. After high-temperature and high-pressure sterilization, not only the meat quality and bones of the fish are softer, but also a large amount of calcium is dissolved out. The calcium content of a box of canned fish can even be 10 times more than that of fresh fish with the same weight, and minerals such as iron, zinc, iodine and selenium in fish meat will not be lost.

Why can’t "fat" cans be eaten?

In most cases, consumers are advised to buy products from regular manufacturers in large shopping malls or supermarkets, and judge the quality of canned food from the aspects of appearance, packaging, sensory quality, label and brand.

Wu Xiaomeng reminded that the cans of normal metal cans should have a complete shape, no deformation, no damage, no rust spots and a concave bottom cover; The center of the metal cover of the glass bottle can should be slightly concave downward, and the contents should be complete in shape, clear in soup and free of impurities when viewed through the bottle body.

What needs special reminder is that if you encounter the following situations, no matter how attractive the contents of the can are, don’t eat it.

One is canned "fat listening", that is, expanding cans. The main reason for tank expansion is that the inside of the can is polluted by microorganisms and produces gas. When these gases gather to a certain extent, the can will be deformed. Therefore, the can’s "getting fat" is a very obvious danger signal that it has gone bad.

Second, the canned packaging is leaking and moldy. In the process of storage and transportation, canned products will be deformed due to bumps and other reasons, and the seal of the can cover will leak, which will lead to the contact between the products in the can and the outside world, and microorganisms may take the opportunity to enter.

The survey found that 93.21% of the respondents had the right choice. However, about 7% of the respondents still thought that the collision caused by transportation was not a big problem and chose to buy and eat.

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

As for canned sugar sauces and jams, the sugar content is generally 40%-65%. Relatively speaking, it is not easy to deteriorate after opening, but it is still not careless. If you can’t eat it all at once, you should cover the jar, or pour it into other containers and seal it with plastic wrap, and then put it in the refrigerator for preservation. Try to eat it in two or three days. In autumn and winter, it can be stored for a few more days. (Reporter Li Jian)