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Canned food has been favored by consumers in many countries for many years because of its relatively small changes in nutrients and flavor during processing, as well as its cleanliness and ease of consumption. However, whether canned food can lock in freshness and nutrition has always been a topic of controversy. To clarify this problem, we must first understand how canned food is produced and what processes are used.
Processing nearby to maintain the freshness of ingredients
As early as 1997, American scientists conducted a comparative study of various nutrients in fresh, frozen, and canned vegetables and fruits. The results of the study found that the content of vitamin C, B vitamins and polyphenolic compounds in canned fruits and vegetables is indeed lower than that in fresh and frozen fruits and vegetables. However, during storage, the content of these nutrients in fresh and frozen fruits and vegetables decreases much faster than canned fruits and vegetables. Both fresh and frozen vegetables are raw and can only be eaten after cooking. During the cooking process, these nutrients will be further reduced, while canned fruits and vegetables do not need to be cooked again when they are eaten. In addition, the contents of other nutrients such as carotenoids, vitamin E, inorganic salts and dietary fiber are similar in canned fruits, fresh fruits and frozen fruits and vegetables.
Take fruits as an example. Fruits are seasonal foods. After the season, fruits on the market generally need to be stored in plastic bags and air-conditioning and heat preservation. Even so, the nutrients of the fruit will gradually be lost in the process of its own respiration, and the freshness will also decrease. The processing of canned fruits is carried out when a large number of fruits are harvested, and it usually only takes a few or ten hours from picking to processing, so the freshness and intact state of the fruits are kept to the greatest extent. After processing, sterilization and enzyme inactivation can completely block the biological changes of fresh fruits during storage. In order to ensure the freshness of the ingredients, most canning factories are located in places where the raw materials are concentrated. Such a "nearest processing" layout not only shortens the transportation distance and reduces costs, but more importantly, locks the best ingredients in a can.
Essential nutrients are retained
canned food is usually pasteurized, and its sterilization temperature is generally 120 ℃, while the sterilization temperature of canned vegetables and fruits is lower, generally 80 ℃-90 ℃. At this temperature, most of the nutrients in the can can be well retained, and only a few nutrients that are not heat-labile, such as vitamin C, vitamin B6, and vitamin B9, will be destroyed. However, in the cooking process, these nutrients are also easily destroyed by high temperature.
Vitamin A: Carotene has a stable structure during the production process of canned food, with little loss. Studies have shown that heating is more helpful to the stability of its structure;
Vitamin C: Although part of this element will be lost during the heating process, it is only decomposed in a large amount in the aqueous solution, and the remaining vitamin C will still exist in a stable form during the shelf life of the product;
Folic acid: The stability of folic acid corresponds to vitamin C;
Vitamin B1: In the process of making canned beans, the loss of vitamin B1 is less than that in the cooking process;
Potassium and Calcium: The content of these two elements will not change during the production process of canned food;
Dietary fiber: Not only does the canning process have no effect on the substance, on the contrary, it can also promote its dissolution, strengthen its structure and organization, so that it is more conducive to its absorption by the body.
Different raw materials adopt different processes
The basic processing flow of canned food generally includes the selection of raw materials, cleaning, peeling, cutting, pre-cooking, adding auxiliary materials, sterilization, exhausting, cooling, packaging, etc.
The selection of raw materials is more important, which is the basic link to ensure the quality of canned food processing. According to the requirements of canned food, fresh, appropriate size and maturity food materials are selected. The surface of the raw materials should be free of disease and mechanical damage. The dried, rotten and unqualified raw materials are eliminated to facilitate subsequent operations. For some ingredients, peeling is required, such as yellow peaches and oranges. In the peeling process, pay attention to the protection of the pulp, keep the original shape, and treat the damaged part separately. In this link, there are still some food materials that need to be pitted, such as hawthorn. When pitting, the principle of reducing waste must be adhered to and the original shape of the raw materials must not be damaged. Some ingredients are large and need to be cut into small pieces for storage and consumption. When cutting, according to the needs of the canned food packaging, combined with the characteristics of the food, the appropriate cutting method and size are adopted, and the parts damaged by the cutting must be treated separately.
In the pre-cooking stage, it is necessary to select the appropriate temperature and time according to the variety of the ingredients to ensure their maturity.
Adding auxiliary materials is to ensure the unique taste of the can. All auxiliary materials need to undergo quality inspection and be added in strict accordance with national standards. Sterilization, exhaust, and cooling are the most critical links. Sterilization is related to the shelf life of canned food. For different canned foods, the sterilization process used is also different. The last step is to make a canned product and package it for storage.
Currently, under the application of new technology, canned food not only guarantees product safety and nutrition, but also has good color, taste and shape. It can be stored for a long time at room temperature and is easy to carry, which further meets people's needs for a better life.