At 7:30 on the 17 day, the long march of the Shenzhou eleven manned spacecraft two F remote eleven launch rocket was ignited at the Jiuquan satellite launch center, and Jing Haipeng and Chen Dong opened the longest space residence of Chinese astronauts to date. According to Cao Ping, deputy director of the astronaut center space nutrition and food research office, the 33 days of the flight mission, the astronauts have more than 100 food, including staple food, staple food, instant food, drinks, condiments and functional food products of six categories. The shelf life is generally over one year, but it does not contain preservatives. It can provide ample energy and nutrition for astronauts at the same time. In this way, preservatives can be preserved for about a year, so the average quality of canned food for ordinary people is also very long. Does it contain preservatives?

Canned preservatives do not need to be added

Fan Zhihong, a doctor of food science at China Agricultural University, said that in addition to ensuring the convenience of space food in space, the food science also pays great attention to avoid pathogenic microbes. Many foods should be treated by high temperature sterilization or irradiation sterilization, but also pay attention to no waste and residue. Space food experts have repeatedly revealed that, in addition to the natural food and the original low water content food, the astronauts also include frozen and dried food, canister and so on. The shelf life of many foods is over one year. From the astronauts' food, people can clarify some rumours which are heard everyday: long shelf life does not mean that food must be added with preservatives.

In fact, the principle of making cans is simple: when the raw materials and canned containers are fully heated and germicidal, they are sealed by heat, and then reheated and sterilized. After cooling, the air volume in the top clearance of the container will shrink and produce negative pressure, so that the originally sealed bottle cannot open, and the bacteria outside can not go in. After these processes, food naturally does not decay, so there is no need to add preservatives.

Processing is not equal to no nutrition

Making reasonable canned food is not a nutritional waste. Irradiated food will not affect the health of the consumer.

General meat and seafood can be pasteurized, so the processing temperature is about 120 degrees Celsius. And buying home processing program is also very simple, just heating. So, to a certain extent, the loss of canned food is much less than that of family cooking (cooking is easy to exceed 200 degrees Celsius). The processing temperature of canned vegetables and fruits is not more than 100 degrees, and the nutrition is relatively preserved.

In addition, raw materials for canned food are fresh. To make canned food, in order to pursue lower cost and better taste, we will choose the freshest raw materials in the most suitable season. Moreover, in order to save costs, regular canning manufacturers have their own raw material bases and build their production lines near the base. This is equivalent to the fact that it is now being done from its own backyard, greatly reducing the process of picking, transporting and processing, and the general process does not exceed 6 hours. And high temperature heat treatment will stop or slow down the chemical reaction of nutrient loss, and keep the freshness and nutrition of food.

How should the canned food be selected?

Don't have a "oil trademark"

Observe whether the package is complete, whether there is leakage, whether the lid or bottle cap is rusty or bruised, and whether the trademark is soaked.

Do not buy "fat listening"

Observe the bottom of the tank, the lid of the tank, or the cap of the bottle. The lid of the pot and the cap should be concave. If you find the lid of the pot and the top of the bottle, do not buy it.

The sound is crisp and bright

Use the hand to hit the lid of the tank. When the sound is crisp, the quality is excellent, while the voiced sound indicates that it has deteriorated.

The trademark should be complete

Observe the production date and shelf life of the product. When the trade mark is incomplete or near the expiration date, the product must be discreet when buying.