Freeze Dried Fruit And Vegetable Powders are lightweight and easy to carry and transport. Colorful freeze-dried green fruit slices, freeze-dried convenient instant soup, freeze-dried dehydrated seafood, vegetables and so on can be found everywhere. Vacuum freeze-drying (vacuum freeze-drying) technology in the food industry has been described as one of the important symbols of technological progress in the food industry in the 20th century. So what is the development trend of freeze-drying fruit and vegetable technology and products?
What Is The principle of Freeze Dried Fruit And Vegetable Powders technology?
Water can be in solid, liquid and gaseous state 3 states. When the atmospheric pressure is reduced to a certain level (610.5 Pa), the boiling point of water and the freezing point coincide. At this time, water molecules can be realized at low temperatures from ice to the direct transformation of steam, this process is known as water sublimation. Vacuum freeze drying technology is by freezing the wet material below the eutectic point temperature. It utilizes the principle of water sublimation, the drying technology that directly removes the water molecules in the material under low-pressure conditions. And the water vapor sublimated in the material is captured by the water vapor condenser in the vacuum system. Thus obtaining a long storage period. System stability and nutritional function of complete dehydration products.
Freeze-drying process can be divided into three main stages. They are pre-freezing stage, sublimation drying stage (the first stage of drying) and resolution drying stage (the second stage of drying).
• Pre-freezing stage:
This stage mainly freezes a large amount of free water in the wet material into a solid state. Generally according to the different materials to determine the appropriate pre-freezing temperature of the co-melting point. As the material is in the frozen state. The material system is in a stable state. There is a significant correlation between the pre-freezing rate and the type of freeze-dried material. Quick freezing forms smaller ice crystals and has less effect on the cellular structure of the material. In contrast, the slow freezing freeze dried fruit and vegetable powders process generates larger ice crystals. Larger pore-like structures are left behind, thus favoring water sublimation. However the larger ice crystals will destroy the original structure of the cells. It has a certain effect on the organizational structure of freeze-dried fruits and vegetables and related bioactive substances.
• Sublimation drying stage (first stage drying):
This stage requires appropriate warming of the material. Make the material in the frozen state of the free state of water sublimation. About 90% of all water in the material is removed during this period. Different fruits and vegetables due to its own material composition, moisture content, moisture distribution and moisture state and other characteristics of the differences. Resulting in the sublimation of water at this stage of the heat required there are also differences. The stage needs to ensure that the temperature can not exceed the material's own co-mingling point temperature, but also more than the sublimation temperature of water. If the sublimation temperature is too much above the eutectic point. Materials will be due to the system of water viscosity reduction and volume collapse, discoloration, bubbles and other phenomena. Therefore, the sublimation temperature of fruits and vegetables to close to the eutectic point, at the same time more than the water sublimation point is appropriate.
• Resolution drying stage (second stage drying):
Based on the previous stage, this stage continues to remove about 10% of the bound water sublimation that was not removed in the first stage. This stage requires a high enough vacuum to ensure that the resolved bound water has sufficient power to escape from the material. In addition, since the resolution of the bound water requires a high level of energy, it is necessary to ensure that the temperature in this stage reaches a certain level. Due to the material composition, shape and residual water content of different materials, the specific resolution time needs to be determined by the basic properties of specific materials.
What Is Vacuum freeze drying technology development trend?
(1) freeze-drying fruits and vegetables processing suitability research
Different varieties of fruits and vegetables have different color, texture, flavor and nutritional functions. Make different varieties of raw materials freeze-dried products of different qualities, not all raw materials are suitable for freeze-drying. In terms of freeze-drying fruits and vegetables, with different material basis of raw materials, will significantly affect its suitability for processing in the freeze-drying process. The material composition and organizational structure of the material itself also has a greater impact on the quality of freeze dried fruit and vegetable powders. Because the material after freeze-drying has lost most of the water. Therefore, the material composition of the raw material itself determines the final color, flavor, texture and nutritional function of the freeze-dried product.
• Freeze-drying quality formation mechanism and control technology
First of all, it is the quality formation mechanism and control technology of color, flavor and texture. The color change of hot air drying is usually related to product browning (enzymatic or non-enzymatic reaction) or pigment degradation. Unlike conventional hot air drying, color changes during freeze drying may be due to the presence of pore structures in the freeze dried sample. These structures scatter the reflected light, causing the color to change. Shrinkage or collapse of frozen foods due to removal of moisture is a major problem in the sublimation stage. Lower sublimation pressures (higher vacuum) can often reduce the rate of food crumpling and produce freeze dried fruit and vegetable powders with lower packing densities and more porous structures. In addition, the formation of ice crystals during the pre-freezing stage may disrupt the cellular structure of the sample. This results in a softer texture of the product. Slower freezing speeds can lead to greater ice crystal formation. This leads to more cellular disruption during freezing and the development of softer texture characteristics.
And this disruption of the tissue integrity of the various fruits will result in less firmness of the fruit samples. The second is the nutritional functional quality formation mechanism and regulation technology. Since the dehydration process of freeze drying is carried out under low temperature conditions without liquid water. Therefore, compared with traditional drying methods, freeze drying technology greatly reduces or eliminates microbial activity and chemical reactions. It has been found that the loss of bioactive compounds (such as total flavonoids, flavonols, catechins and phenols) in freeze-dried samples is negligible.
• Pre-treatment energy-saving low-carbon technology
Material pretreatment can effectively improve drying efficiency. To achieve the purpose of optimizing product quality, reducing energy consumption and reducing carbon emissions. For example, before freeze-drying, the use of ultrasonic pretreatment. Through the thermal energy and ultrasonic cavitation effect generated by the interaction between ultrasonic waves and media. Form microporous channels in the material. Quickly remove part of the moisture in the material. Shorten the drying time and achieve the effect of reducing energy consumption. In addition, combined with high-voltage pulsed electric field treatment, it can improve the permeability of the cell membrane on the basis of the material's organizational structure is not destroyed. This effectively shortens the freeze-drying time and reduces the operating cost. At the same time, there are also research findings on vacuum cooling pretreatment of freeze-dried materials. It can form microporous channels in the surface layer of the material, thus reducing the resistance to sublimation of ice crystals inside the material, improving the sublimation speed and shortening the drying time.
• Vacuum freeze drying technology
Vacuum freeze-drying technology and other drying technologies can make up for the shortcomings of a single freeze-drying technology with high energy consumption. At the same time can also obtain high-quality freeze-dried fruits and vegetables. Vacuum freeze drying joint drying technology is based on the basic characteristics of the material, the two or more drying technologies to complement each other's advantages as the principle of dehydration of the material in stages, in order to reduce the operating costs of material drying, improve the quality of the freeze dried fruit and vegetable powders and retain the physical and chemical properties of the material to the maximum extent.
• Energy-efficient and low-carbon vacuum freeze-drying equipment
As mentioned above, energy consumption is a long-standing problem in freeze drying. As the electric heating system mainly provides energy for the sublimation of solid water in wet materials. It consists of only several electric heaters, so the space for energy-saving transformation is relatively small. At present, the refrigeration system of domestic vacuum freeze drying equipment generally adopts two-stage compressor refrigeration system and overlapping compression low-temperature refrigeration system. The former is mainly applicable to large-scale medium-sized vacuum freeze-drying equipment, water-cooled form of work. The latter is mainly applicable to small vacuum freeze drying test equipment. To air-cooled form of operation, both modes of operation need to be equipped with fans and water pumps. At present, in order to achieve the purpose of energy saving and low carbon. The new refrigeration system can be utilized to replace the traditional fixed-frequency pumps and fixed-frequency fans with variable frequency pumps and variable frequency fans. In addition, in view of the capacity difference between small freeze dryers and medium and large freeze dryers. Variable capacity compressors can be used. Such as in the small test vacuum freeze drying equipment using scroll compressor to replace the piston compressor, and in the medium and large medium-sized equipment using screw compressor to replace the piston compressor, so as to make the compressor and vacuum freeze drying machine energy matching, to achieve the role of reducing energy consumption and so on.
Guanjie has our own factories and independence freeze dried production lines. And we have been focusing on it freeze dried fruit and vegetable powders for 20 years. If you are interested in our dry fruit, welcome to enquiry us: info@gybiotech.com.
