Pick? Abstract: At present, freezing and cold storage technology has been widely used in food processing industry, and quick-frozen food has also become human.

A kind of processed food that children like very much. This paper expounds the mechanism of food refrigeration, briefly introduces the development history of refrigeration technology, and studies the refrigeration processing technology of fruits and vegetables, livestock products and common aquatic products in today's food industry. The development of frozen food industry at home and abroad at this stage is described. Finally, in view of the problems existing in the development of quick-frozen industry, the corresponding countermeasures are put forward. ?

Key words: food freezing and cold storage; Frozen food; Food preservation; Food processing?

Foreword?

Frozen and refrigerated food industry is a new food industry rising with the development of social economy. At present, the industry has developed into a diversified and large-scale food manufacturing industry, which is an important part of modern food industry. Frozen and refrigerated food has become an indispensable part of people's modern diet and life, and is increasingly becoming one of the mainstream foods. At the same time, the frozen and refrigerated food industry has become the main industry of economic development in some areas, which has played an important role in promoting the deep processing of agricultural products, realizing the industrialization of agricultural production and solving the problems of agriculture, countryside and farmers [1]. ?

First, the mechanism of food freezing and cold storage processing?

As an industrial-scale food preservation method, food freezing has been widely used all over the world. The mechanism of food freezing and cold storage is that at the low temperature below 0℃, the life activities of microorganisms are significantly inhibited, thus preventing food from spoilage. Secondly, at low temperature, the speed of all reactions, such as enzyme reaction and oxidation reaction, which affect food quality, decreased significantly. In addition, the formation of frozen crystals in products is also the activity of microorganisms and the decrease of water activity in metamorphic reaction [2]. ?

The so-called quick freezing is to quickly freeze the central temperature of food to-1℃ to -5℃? It takes no more than 30 minutes to pass through the maximum ice crystal generation zone. For foods with high water content such as fresh fish and livestock meat, when the product temperature reaches-65438 0℃, the water in the food begins to freeze and the temperature drops to -5℃? When, 80% of the water content is frozen. At this time, the whole food is almost frozen. Therefore, the temperature limit of 1℃-5℃ is called the maximum freezing speed of the ice crystal formation zone, which is defined as the distance from the food surface to the central point divided by the quotient of the time required for the temperature of the central product to drop from-1℃ to -5℃, generally expressed in cm/h [3]. ?

Second, the development history of refrigeration technology?

/kloc-the emergence of artificial cold source at the beginning of the 0/9 th century made the development of food freezing and refrigeration epoch-making. 1834 British Jacob? Perkin invented the compression refrigerator with ether as refrigerant, which is the first practical refrigerator in the world. 1872 American Carrey invented a compression refrigerator with ammonia as refrigerant and water as absorbent. 1872 Americans David and Boyle and German Carl? Feng? Lnde independently invented the compression refrigerator with ammonia as refrigerant. These freezers were used as ice makers at that time to replace natural cold sources [4]. ?

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1877- 1878 French Charles? In order to transport beef and mutton back to France from New Zealand, Argentina and other countries, Teller began to use ammonia absorption refrigerator to cool the beef first, and then freeze the beef and mutton to solve the problem of keeping the meat fresh by sea for a long time, which is the first time that frozen food came out as a commodity [5]. ?

Since 1930, a large number of non-toxic and tasteless freon refrigerants have been used in household refrigerators, which is less dangerous than ammonia. But freon is easy to destroy the ozone layer, so refrigerants such as lithium bromide and hydrofluorocarbons are introduced. ?

In the 1970s, refrigeration technology with liquid nitrogen and liquid carbon dioxide as refrigerants appeared, which can be directly sprayed on the surface of food, not only for rapid refrigeration, but also for deep refrigeration. For example, the low temperature of-196℃ can be obtained by using liquid nitrogen [6]. ?

Three, all kinds of food refrigeration technology?

(1) quick-freezing technology for fruits and vegetables [7]?

1, process?

Raw materials → pretreatment (material selection, cleaning, grading, peeling and dicing) → blanching → cooling → draining → quick freezing → packaging → refrigeration → transportation and marketing? 2. What are the key points of operation?

Raw materials should have excellent flavor, color, ideal texture, uniform maturity, insect resistance, high yield and suitable for mechanical harvesting; The key to blanching is: the temperature and time of heat treatment; After blanching, it should be cooled quickly, which can be divided into water cooling and air cooling. After blanching and cooling, there is a certain amount of water on the surface of raw materials, which should be removed, otherwise it is not conducive to rapid thawing and packaging after moving; Quick freezing requires that the raw materials of fruits and vegetables quickly pass through the maximum ice crystal formation zone in a short time, and the center temperature of quick frozen products should be below-18℃ to ensure the quality. Packaging can control and prevent some deterioration of food during storage, which can be divided into inner, middle and outer packaging; Frozen food is generally stored in cold storage, which requires stable temperature. The lower the temperature, the better the quality; In the process of transportation and marketing, the temperature should be kept low, and the transportation time should be controlled at-65438 08℃, generally at-65438 05℃. ?

(2) Processing technology of common quick-frozen aquatic products [8]?

1, frozen shrimp?

Raw material acceptance → raw material storage → shrimp skin acceptance → cleaning → soaking → enzyme inactivation → cooling → specification → freezing → ice compress → metal detection → packaging → refrigerated transportation? 2. Quick-freeze a single lobster?

Fresh shrimp → selection → cleaning → classification → high temperature cooking → low temperature cooling → hulling → quick freezing of monomer → metering → packaging → refrigeration?

3. Quick-frozen squid?

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Raw material acceptance → laparotomy to remove dirt → cleaning → classification → drainage → weighing → salt water fixation → tray loading → semi-finished product inspection → quick freezing → tray → ice coat → packaging → inspection → refrigeration? 4. Quick-frozen whitebait?

Large whitebait → rinsing → intestine cleaning → screening → soaking → weighing → bagging → adding water → quality inspection → plate loading → quick freezing → bagging → quality inspection → finished product? 5. Frozen snail meat?

Raw material acceptance → grading → cleaning → removing impurities and tail intestines → full rinsing → draining → weighing → bagging and sealing → quick freezing → boxing → cold storage? 6. Frozen oysters?

Oyster selection → cleaning → soaking, sand spitting → opening the shell to take meat → grading, inspection → rinsing → draining → freezing → freezing → vacuum packaging → freezing storage? 7. Frozen eel slices?

Procurement and transportation → selection → live killing and bleeding → tail cutting and bleeding → soaking and bleeding → viscera removal → cleaning → ice water preservation → ice water cleaning → dorsal fin, anal fin and caudal fin removal → boneless, head and tail removal → fish fillets → specifications → rinsing → plate setting → quick freezing → weighing → ice compress → bagging → packaging → refrigeration? 8. Frozen butterfly shells?

Raw materials → keeping alive at low temperature → cleaning → breaking the shell to take meat → taking axe feet → cleaning → opening slices → removing dirt and shaping → sorting → cleaning → weighing → loading plates → precooling → quick freezing → taking off plates → packaging → inspection of finished products → refrigeration?

(3) Frozen storage technology of livestock and poultry meat [6]?

1, freezing method?

Static air freezing method; Plate freezing; Air-cooled quick freezing II. Freeze the winter storage process?

1), two-stage freezing process?

The processed carcass is first sent to a cooling chamber for cooling, and then sent to a freezing chamber for freezing when the carcass temperature drops to 0-4℃. After 20-24 hours, under the conditions of room temperature -23-25℃ and air velocity of 2-3 m/s, the temperature of the central muscle of the hind leg can be reduced to-65438 05℃. Most countries, such as China, use two-stage freezing technology to freeze meat. ?

2) Direct freezing process?

That is, after livestock are slaughtered, processed and sorted, they are put into the meat cold room for grading and temporary storage, and the surface moisture is removed by blowing in the meat cold room. When the carcass meat accumulates to the volume equivalent to a freezing room, the freezing with the storage temperature below-15℃ will be promoted rapidly.