Quick-frozen fruits and vegetables began to appear in the 1930s, but because of the good effect of quick-frozen, long storage time, ready to supply, easy to eat, and rapid development. Especially in the past 20 years, with the improvement of people's living standards, the popularity of cold chain transportation and household refrigerators, the development of quick-frozen fruits and vegetables is more rapid, and the demand of the international market is also increasing.

At present, China has become a major export producer of quick-frozen fruits and vegetables, with more than 300 export production enterprises. The vast majority of products are sold to European and American countries and Japan, with annual foreign exchange earning more than 200 million US dollars. Japan and the United States import the largest amount from China, and increase year by year. The reason why China's quick-frozen fruits and vegetables have strong competitiveness in the international market is that China's labor costs are low and raw materials are cheap. Therefore, China's exports of frozen fruits and vegetables to Japan and the United States are increasing day by day. Quick-frozen fruits and vegetables are also very popular in China, and the consumer market is expanding rapidly. There is broad market space for both domestic and export sales. 2b6534336a21a17f67f8c60784be 3d97_2257-120324000927.jpg

Quick-freezing is a fast-rising food preservation method in recent years. It is also an effective way to protect the color, aroma, taste, shape and nutritional health functions of food, especially in prolonging the storage time of fruits and vegetables and reducing wastage. As a method of food preservation, freezing or quick-freezing can effectively prolong the storage period of food, which can be adjusted.

Quick-freezing is a fast-rising food preservation method in recent years. It is also an effective way to protect the color, aroma, taste, shape and nutritional health functions of food, especially in prolonging the storage time of fruits and vegetables and reducing wastage. As a method of food preservation and storage, freezing or quick-freezing can effectively prolong the storage period of food, which can not only adjust the market supply to meet consumer demand, but also increase the income of fruit and vegetable farmers.

The requirements for quick freezing and refrigeration are different. In terms of temperature, the freezing temperature should be - 18 C or lower, while the refrigeration temperature should be about 0 C. When food is frozen, microorganisms do not grow and develop, while refrigeration can only inhibit some microorganisms. Strawberries, lychees, cherries, waxberries, apples, pears, grapes and watermelons packaged in quick freezing packages are quickly put into the freezer at - 18 C to - 20 C for freezing storage. The shelf life can reach one year or even several years, while the refrigerated food can only be stored for a few days, up to a few weeks.

At present, the protection of environmental protection is becoming more and more stringent. Many people in the frozen processing industry will feel anxious about the prohibition of liquid ammonia, because liquid ammonia and Freon are commonly used refrigeration raw materials for traditional refrigeration processing equipment. So far, without refrigeration raw material supply, they are somewhat restless.

When liquid ammonia and Freon become common refrigeration raw materials in the refrigeration industry, a new type of refrigeration raw materials is also slowly rising, that is, liquid nitrogen. N2 is a non-toxic, colorless and tasteless inert gas. It is difficult to react with other gases and substances at room temperature. This is why we can often see the bags of potato chips bulging in supermarkets. It is because the bags are filled with N2 to keep the freshness and taste of potato chips. In fact, this is also one of the characteristics of liquid nitrogen quick-freezing refrigeration. The products frozen with liquid nitrogen as refrigeration raw material can maintain the quality and freshness of the products as high as 99%. So some people say that "liquid nitrogen as refrigeration material is the best choice for refrigeration of seafood, fruits and vegetables, meat, cooked food, medical field and space equipment."

Another characteristic of 816718389257329500.jpg liquid nitrogen as refrigeration raw material is its refrigeration speed and short freezing time. It can cross the ice crystal node of the product, spray refrigeration seamlessly and form uniform fine ice crystals inside the product, lock up the moisture and nutritional value of the product, so that the production efficiency and product quality and nutritional value can be improved, which is based on fluorine. Leon and liquid ammonia are unprecedented refrigeration materials for quick-freezing equipment. Many insiders believe that in the future development trend of quick-freezing refrigeration industry, liquid nitrogen as refrigeration raw material may replace Freon and liquid ammonia, and become the development direction of refrigeration industry. The liquid nitrogen quick-freezing machine selected Guangzhou extremely fast, brand products, many years of experience, professional and technical excellence, has a good reputation in the quick-freezing industry.

The quick-frozen knowledge below with everybody popularizes:

1. Quick freezing principle

Freezing is a fresh-keeping method that extracts heat or energy from products until the melting latent heat of free water molecule is eliminated, and water becomes ice crystal structure. It can effectively inhibit the activity of microorganisms and enzymes. It is an important refrigeration method in modern fruit and vegetable processing industry.

Water in fruits and vegetables is not pure water, but a mixture of organic and inorganic substances. These substances include salts, sugars, acids and more complex organic molecules, such as proteins and trace gases. Therefore, fruits and vegetables need to drop below 0 C to produce ice crystals, and the temperature at which ice crystals begin to appear is called freezing point or freezing point. When the temperature of liquid drops to freezing point, the liquid phase and crystallization coexist in equilibrium. In order to make the liquid crystallize, it is necessary to break the equilibrium state, that is to say, the temperature of liquid phase must be reduced to a little lower than the temperature of ice junction. When the liquid is subcooled, it is stimulated by some stimulus.

After the formation of the stable crystallization center, if the heat dissipation continues, the ice crystal will continue to increase. The heat released by the phase transformation during crystallization makes the temperature of water or water solution rise from supercooled temperature to freezing point temperature, and the liquid becomes solid, which is called ice. Icing includes two processes: nucleation and nucleation. Nucleation is the formation of particulate particles by orderly binding of a few water molecules. The size of crystal formation depends on the number of nuclei and the freezing rate. Under quick-freezing conditions, nuclei were widely formed inside and outside fruit and vegetable cells, forming a large number of nuclei, which were acicular crystals with uniform distribution. This distribution will not damage the cell tissue, easy to restore the original condition after thawing, and better maintain the original quality of fruits and vegetables. After thawing, the number of ice crystals will decrease, the increase of ice crystals will damage cell tissues, the juice will flow out after thawing, the texture will rot, and the flavor will disappear, which will affect the quality of products. Therefore, in the process of quick-frozen storage, we should avoid temperature fluctuation, otherwise, even quick-frozen products will lose the advantages of quick-frozen. Grasping the principle of quick-freezing has a positive significance for commercial fruit and vegetable quick-freezing preservation.

2. Quick freezing process

The quick-freezing principle of fruits is basically the same as that of vegetables. The biggest difference is that most fruits do not need to be blanched, while most vegetables must be blanched. Taking fruit as an example, the technological process of quick-frozen preservation is as follows:

Raw material picking selection cleaning peeling pedicling denucleation grading cooling sugar or vitamin C quick freezing weighing packaging quick freezing storage transportation sales.

3. Operating Points

(1) Fruit is blanched with sugar instead of hot water. Fruit is soaked in syrup with or without vitamin C instead of hot water to prevent mildew growth. Generally speaking, single quick-frozen fruits do not need blanching. Some fruits, such as peaches and apples, often brown in the process of quick-frozen. Even after soaking with sugar, after a certain period of storage, discoloration still occurs. In order to prevent fruit browning and maintain its original color, vitamin C with a mass fraction of 0.1%~0.5% should be added into the sugar solution.

(2) Fruit must be frozen rapidly after being cooled and dried. The commonly used cold air temperature is -30 ~40 C, and the wind speed is 2 m/s~17 m/s. When frozen, the cold air is forced to blow from the bottom to the top of the mesh belt at sufficient speed. The strong air flow will suspend the product. Like boiling fluid, the cold air can contact the product particles directly, the heat exchange is greatly strengthened, and the freezing speed is accelerated. For fruits, it is generally not necessary to use the fluidized bed single freezer, because this freezer has the hidden danger of damage to fruits, the most commonly used is the granular freezer - mesh belt freezer. During the freezing process, the uneven accumulation of fruits should not be ensured.

(3) The whole circulation link should be frozen below - 18 C in order to keep the circulation link in a low temperature state.

4. Food thawing

Frozen food should be thawed and restored before use. Thawing and freezing are two opposite heat transfer processes. The thawing of non-liquid food is slower than freezing. Frozen food should be thawed before eating, but should not be stored for a long time after thawing. The faster the thawing process is, the better. Thawing can be done in refrigerator, room temperature, cold or warm water, or by microwave method. Microwave thawing is uniform and rapid, but the tissue composition of the treated fruits and vegetables should be uniform and uniform in order to achieve good thawing effect.

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