Today, when healthy eating is receiving much attention, canned food is not favored by Chinese people. Few people are interested in canned food on supermarket shelves, and they are rarely seen in family meals. Some people even regard canned food as a representative of unhealthy food. However, people obviously misunderstand canned food. In fact, they are not only delicious and nutritious, but also hygienic and safe.
The most fundamental feature of canned food is the use of sealing and high-temperature sterilization technology, which eliminates pathogenic bacteria and spoilage bacteria. It is a thorough revolution in food storage and long-term supply in the food industry. Since the birth of canned food, it means safe food. Since canned products eliminate the factors of food spoilage, they are a type of food that does not need or allow the addition of any preservatives. No matter how the canning processing technology is improved, safety is the primary feature and basic element of canned food. According to the US FDA, none of the more than 4,000 foodborne illness reports in the US between 2007 and 2012 were related to canned food.
Canning generally uses the following process: food is processed and put into cans, and after the exhaust step, the food temperature reaches more than 80°C; then, the cans are sealed by electric welding to make the cans vacuum; then, the cans are placed in a furnace and heated to 135°C for up to one and a half hours to ensure that all bacteria in the cans are killed under the high temperature; the cans after heating and sterilization are cooled before being stored in the warehouse; the warehouse is kept at a room temperature of 25°C for 7 to 14 days (this temperature is most likely to allow bacteria to grow), and the spoiled cans during this period will be thrown away to avoid entering the market.
Scholars from the University of California, USA, compared the nutrients of canned fruits and vegetables with those of fresh and frozen fruits and vegetables, and found that fresh fruits and vegetables can only provide various vitamins and minerals to the human body when they are just picked, but oxidation during storage will lead to loss of nutrients, so the nutrient loss caused by cooking and storage is higher than expected. However, commercial canning and frozen storage can maintain the main nutrients.
In the initial heat treatment stage of canning, water-soluble and oxygen-labile nutrients such as vitamin C and vitamin B may be lost, but these substances are relatively stable due to the lack of oxygen in the later storage of canned products. At the same time, the study also found that the retention of vitamins K, E, A and D in canned products is relatively stable. At the same time, the changes of phenolic substances, which are also water-soluble and oxygen-labile, were also studied. It was found that the situation was more complicated. Storage and cooking would lead to the loss of such substances, but the heating of the pre-treatment of canned processing would help to increase the polyphenol content and antioxidant activity in tomatoes. Comparison of minerals and cellulose found that minerals and cellulose generally remained stable during processing, storage and cooking, but the loss was greater during peeling and other links. The study of carotene in fresh corn and canned corn also showed that the content of lutein, zeaxanthin and total carotenoids was basically the same and there was no significant difference, indicating that canning processing did not reduce the carotene content in corn. The reason is that the factory-based canned vegetable production takes less time and less loss from picking to processing into stable quality products, while the time for home cooking to enter the home after the vegetables are picked is longer than the time from factory production to processing, so the nutritional loss after picking is greater, and the processing loss of the home is greater than that of the factory production.
First of all, the ingredients used in canned food are fresh. In order to pursue lower costs and better taste, the freshest ingredients are selected in the most suitable season. Moreover, regular canning manufacturers have their own raw material bases, and have strict control over fertilizers, pesticides, etc., which can fully guarantee the quality of raw materials.
Secondly, the canning process is precisely to "keep" food fresh. If meat and fish are not processed in time, they will quickly rot. If vegetables and fruits are not processed in time after picking, they will also cause continuous loss of nutrients. Studies have shown that after plants are picked, many chemical reactions are reversed because they cannot undergo normal biochemical synthesis, and nutrients such as vitamins will continue to be consumed. Therefore, if the transportation and sales time is too long, the food we thought was fresh will become stale. It only takes less than 1 hour for canned food to go from the field to the factory, from fresh ingredients to finished products. The sterilization process can stop the chemical reaction of food in time, so that the nutrients of food are fully preserved in a fresh state.
