Heat treatment has positive and negative effects on the nutritional value of food. Heating denatures proteins and unfolds peptide bonds. Heating can also swell starch granules, which are susceptible to digestive enzymes, thereby improving digestibility. Heating destroys enzymes in fresh foods and kills microorganisms, thereby protecting nutrients from Oxidation, decomposition and loss. Heating also destroys the natural toxic proteins in food. Raw egg white contains antibiotics, which can be destroyed by heating. Raw soybeans contain antitrypsin factors, phytohemagglutinin and other harmful substances, which also increase the cooking time and reduce the biological value of soybean protein. Therefore, mastering the heating time of beans is the key to increasing the biological value of protein.
The adverse effects of heating are manifested in the destruction of amino acids and vitamins. Some essential amino acids such as lysine, cysteine, color and arginine are easily destroyed by heat. Lysine is most severely affected by heat. The ε-amino group of lysine reacts with reducing sugars in the Maillard reaction to form ε-N-deoxyketulose lysine, which cannot be absorbed and utilized by the human body, thereby making the protein The biological potency is reduced. When cakes are baked at 200°C for 15 minutes, lysine, benzene, acrylic, tyrosine, and serine are destroyed by 5 to 17%, which reduces the biological value of protein. Adding milk to the cakes increases the loss rate.
The heating and gelatinization of starch is good for digestion, but when the starch is cooled, it will condense and age. The aged starch is not easy to be digested. Heating damages the vitamins most significantly. The loss of vitamin B1 in the grain during re-cooking is shown in the table below.
During the heat treatment of canned fruits and vegetables, vitamin C loses 13-16%, vitamin B1 2-30%, and vitamin B2 5-40%. The loss of short-term high temperature is less than that of long-term low temperature. Rapid cooling after heat treatment can reduce the loss. The most serious loss of milk during heating is dimension B1 and dimension C.
Freeze dryer is one of the drying methods, the purpose is to store items. The damage, decay, and deterioration of items are mainly caused by external and internal factors. The external factors are the effects of air, water, temperature, organisms, etc.; the internal factors are mainly the metabolism of biological substances themselves. If the effects of external and internal factors can be reduced to a lower level, the object can be kept unchanged for a certain period of time. Freeze dryers are now widely used in chemistry, pharmaceutical industry, food industry and scientific research, especially in biological medicines containing biologically active substances. What is the difference between freeze drying and conventional drying?
Drying is a very old operation, but the heating and drying of powders and biological products often causes irreversible agglomeration of particles, especially in the preparation of ultrafine powders, the nanoparticles in the liquid phase will coalesce into difficult-to-disperse agglomerates after drying. This is mainly because moisture is emitted from the pores between the particles during the ordinary drying process, and the surface tension causes extremely high additional pressure, which compacts the particles together into agglomerates. The use of a freeze dryer can avoid this problem. Freeze drying is to freeze the gel or blood to be dried into a solid, and then under reasonable conditions, the water is vaporized and removed by sublimation. The gasification process will not affect the agglomeration state of solid particles, so the original particles can be kept intact without being compressed and agglomerated. In addition, the freeze dryer is very suitable for processing biological products, such as blood, because it does not have high-temperature operations. Prevent the deterioration of biological products.
The dried products generally have the problems of reduced volume and hard texture. Most of the volatile components will be lost. Some heat-sensitive materials will be denatured and deactivated, and some materials may even be oxidized. Therefore, there is a big difference in the properties of the dried product compared to the one before drying. The freeze-drying method is basically carried out below 0°C, that is, the product is carried out in a frozen state. Only when the residual moisture content of the product is reduced in the later stage, the product is allowed to rise to a temperature above 0°C, but generally does not exceed 40°C. Under vacuum conditions, when the water vapor is directly sublimated, the drug remains in the frozen ice shelf, forming a sponge-like loose porous structure, so the volume is almost unchanged after being dried by a freeze dryer. Before using again, just add water for injection and it will dissolve immediately.
There are various drying methods in freeze dryers, such as sun-drying, boil-drying, drying, spray drying and vacuum drying, etc., but ordinary drying methods are usually carried out at temperatures above 0°C or higher. The dried products generally have the problems of reduced volume and hard texture. Most of the volatile components will be lost. Some heat-sensitive materials will be denatured and deactivated, and some materials may even be oxidized. Therefore, there is a big difference in the properties of the dried product compared to the one before drying. The freeze-drying method is basically carried out below 0°C, that is, the product is carried out in a frozen state. Only when the residual moisture content of the product is reduced in the later stage, the product is allowed to rise to a temperature above 0°C, but generally does not exceed 40°C. In the freeze dryer under vacuum conditions, when the water vapor is directly sublimated, the medicine remains in the frozen ice shelf, forming a sponge-like loose porous structure, so its volume is almost unchanged after drying. Before using again, just add water for injection and it will dissolve immediately. Compared with conventional methods, freeze dryers have the following advantages:
1. Many heat-sensitive substances will not be denatured or inactivated.
2. When drying at low temperature, the loss of some volatile components in the substance is very small.
3. During the freeze-drying process, the growth of microorganisms and the action of enzymes cannot proceed, so the original properties can be maintained.
4. Because it is dried in a frozen state, the volume is almost unchanged, and the original structure is maintained without concentration.
5. Since the water in the material exists in the form of ice crystals after pre-freezing, the dissolved inorganic salt substances originally dissolved in the water are evenly distributed in the material
Freeze-drying technology (freeze-drying for short) is a new type of food processing technology, which is very healthy and harmless to the human body. Let's take a look at how it is different from ordinary drying:
Ordinary drying is one of the methods to keep the material from deteriorating. There are many drying methods, such as sun drying, boiling drying, drying, spray drying and vacuum drying. However, these drying methods are all carried out at temperatures above 0°C or higher. The product obtained by drying is generally reduced in volume and hardened in texture. Some substances have been oxidized, and most of the volatile components will be lost. Microorganisms will lose their biological vitality, and the dried substances will not easily dissolve in water.
The principle of freeze-drying is well understood. First put fresh fruits and vegetables into a freeze-drying machine at minus 50°C for freezing. After the fruits and vegetables are frozen, vacuum the drying box and increase the temperature slightly after the vacuum is formed. The ice in the fruits and vegetables is directly sublimated into water vapor and separated from the fruits and vegetables, while the "skeleton" of the fruits and vegetables remains unchanged in volume and loose and porous. The moisture that can be removed by freeze-drying can reach more than 95%.
Freeze-drying technology is carried out at low temperature, such as protein, microorganisms, etc. will not be denatured or lose biological vitality. When drying at low temperature, the loss of some volatile components in the substance is very small, which is suitable for some chemical products, medicines and food drying.
During the freeze-drying process, the growth of microorganisms and the action of enzymes cannot proceed, so the original properties can be maintained. Because it is dried in a frozen state, the volume is almost unchanged, the original structure is maintained, and no concentration occurs. Since the drying is carried out under vacuum, there is very little oxygen, so some easily oxidized substances are protected. Drying can remove more than 95-99% of water, so that the dried product can be stored for a long time without deterioration.
Freeze-dried noodles are instant noodles processed by freeze-drying technology and belong to freeze-dried foods. Instant noodles have gone through three eras. The first generation is fried noodles, the second generation is hot air dried noodles, and the third generation is freeze-dried noodles. Freeze-dried noodles are also called FD noodles and FD freeze-dried noodles. FD is the abbreviation of Freeze Dried in English, which means vacuum freeze drying.
Origin of the name
Freeze-dried noodles get their name because they are dehydrated in a vacuum environment at -30°C. The cakes and ingredients of the freeze-dried noodles are all freeze-dried, including the moisture in the noodle soup. Freeze-dried noodles belong to the category of instant noodles, but they are different from instant noodles in terms of production technology and have richer ingredients than instant noodles.
Due to the whole physical process of low-temperature vacuum freezing, sublimation and dehydration, it is characterized by non-fried, flavor-locking, fresh-locking, and aroma-locking, just like cooking in the kitchen.
How to eat
Open the package, tear open the material package, and put the soup cubes on the noodles in the container
Add boiling water to the water injection line and close the lid
Wait for 5 minutes, lift the lid and stir evenly with a fork
The greatest advantage or outstanding advantage of freeze-dried food is that it can be eaten as soon as it is rehydrated. It is an indispensable "logistics" for modern people with high efficiency and fast-paced life. It is reported that freeze-dried food is particularly popular in some developed countries.
At present, due to the huge demand in the domestic market, it provides space for the development of freeze-dried food in my country, and also provides a good opportunity for processing and appreciation of agricultural and sideline products.
According to experts, freeze-dried food can process most foods and medicines, including processing various vegetables, fruits, fish, coffee, tea, Chinese medicinal materials, ginseng, enzymes, serum, bacteria, biological products, aerospace food, etc.
The basic principle of freeze drying is based on the three-state change of water. Water has solid, liquid and gaseous states, and the three phases can be converted to each other and can coexist. When water is at the triple point (temperature of 0.01°C, water vapor pressure of 610.5Pa), water, ice, and water vapor can coexist and balance each other. Under the high vacuum state, using the principle of sublimation, the moisture in the pre-frozen materials is directly removed as water vapor in the ice state without melting the ice, so as to achieve the purpose of freeze drying. Freeze-dried products are sponge-like, no shrinkage, excellent rehydration, and very little moisture. After corresponding packaging, they can be stored and transported at room temperature for a long time. Because vacuum freeze-drying has the unparalleled advantages of other drying methods, this technology has become more and more popular since its inception.
There are various freeze-drying methods, such as sun-drying, boil-drying, drying, spray drying and vacuum drying, etc., but common drying methods are usually carried out at temperatures above 0°C or higher. The dried products generally have the problems of reduced volume and hard texture. Most of the volatile ingredients will be lost. Some heat-sensitive materials will be denatured and deactivated, and some materials may even be oxidized. Therefore, there is a big difference in the properties of the dried product compared to the one before drying.