Nutrition hall

Our reporter Tang Fang

"Doomsday survival can" really eat a lifetime? Surprisingly, the answer may be yes.

Amid the COVID-19 pandemic, Costco, the second-largest retailer in the US, recently launched a "doomsday" canned set. A family can eat hundreds of canned fruits and vegetables, meat and milk for four years. It doesn't matter if they keep more cans.

"In theory, as long as the packaging is not damaged, the cans can be stored forever." Food safety science popularization expert, Dr. Zhong Kai said that the shelf life depends on the physical and chemical properties of food and storage conditions, isolated air, completely inactivated cans can be stored for a long time, 30 years shelf life is "not strange".

Engaged in deep processing of fruits and vegetables research experts, Shaanxi Normal University professor Zhang Baoshan believes that canned food if not from the quality of consideration, itself is no shelf life, but in the long-term storage process, canned food taste, color, quality will change, the content of nutrients will decline.

Launched this canned set, Costco's official website explains that sometimes in the face of natural disasters, it is more safe to stock up on last year's food at home. Some Internet users call it "peace of mind in a can."

"Almost all food can be canned, not only canned fruit in glass, canned meat in tinplate can be canned, supermarket paper packaging, plastic packaging sealed food can be called canned." Zhang Baoshan said that canned is a general term for a class of food that is pasteurized, sealed in an airtight container and can be stored for a long time.

The secret of food's long "standby" is hidden in the process and principle of canning. Popular science writer Yun Xinxin pointed out in an article that canned food can be preserved by first sealing and then thoroughly heating. After being heated for a long time at high temperature, all the bacteria in the canned food are killed. Because it is sealed, the bacteria in the environment cannot enter. Without the seeds, no bacteria can grow, no matter how fertile the food inside the can is.

Most cans have a shelf life of one year, two years, 18 months on the label. "The shelf life is not only about safety, but also about taste and other factors. You can eat it after 10 years, but it may not taste good." Zhong Kai said.

Zhang Baoshan said that as the storage time of cans increases, the food nutrients in them will gradually lose, and the quality will decline. For example, canned fruit in glass bottles will become darker after two or three years of exposure to light. When exposed to heat, the vitamins, polyphenols and sugars in the fruit will undergo chemical reactions. Tinplate packaging of canned meat is opaque, but external collisions, storage temperature changes, etc., will also lead to a decline in the quality of canned meat.

"Can as long as there is no bulge generally no food safety risk, aseptic state is very safe. If there is a bulge, there may be clostridium botulinum and other spores survive, it is not edible." Zhong Kai cautioned.

As a processed food, the process includes canning, venting, sealing, sterilization, cooling and so on. "Now the canning process is mature, the implementation of standardized production, canned meat 121¡æ high temperature sterilization, canned fruit 100¡æ sterilization, mainly to kill clostridium botulinum and other bacillus in the can." Zhang Baoshan said, however, all food after processing, the nutritional quality will decline. Vitamins and other nutrients in canned fruit are not as good as fresh fruit.

Zhang Baoshan said that a long time to eat a single canned is not conducive to health, if you like canned meat today, eat canned vegetables tomorrow, eat canned fruit the day after tomorrow, occasionally drink some drinks, a variety of canned food with food, nutrition balance.

"However, if there is fresh food, it is better to eat less canned food. And the priority is to choose canned food with a short shelf life, but also pay attention to the raw materials." Zhang Baoshan reminded that the sugar water in canned fruit contains 14%-20% sugar, and diabetics should try not to eat it.

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