The importance and use of vacuum freeze dryer in food freeze-drying processing!

The importance and use of vacuum freeze dryer in food freeze-drying processing!
(1) Principle and characteristics of vacuum freeze drying
Principle of vacuum freeze-drying: According to the phase equilibrium theory in thermodynamics, the triple point of water (coexistence of steam, liquid and solid three phases) is 0.0098 °C, and the pressure of triple point is 609.3pa (4.57mm/mg) in water. In the phase transition process, when the pressure is lower than the pressure of the triple point, the solid ice can be directly converted into gaseous water vapor, that is, the ice crystal progresses.
Vacuum freeze-drying is to pre-freeze the material containing a lot of water, crystallize the free water in the substance, freeze it into a solid, and make the ice crystal in the material progress under high vacuum condition after swimming, and then remove the substance after the ice crystal progresses. Part of the adsorption of water, after all, to obtain a dry product with a residual water content of about 1-4%. Vacuum freeze drying is referred to as freeze drying.
(2) Characteristics of vacuum freeze drying skills
The first is that in the process of food boring, it is necessary to control the temperature within the range of minus 40 ° C to minus 55 ° C. It is necessary to make the surrounding environment in a high vacuum state in the process of processing, so this The processing method is very good for the processing of foods with high heat sensitivity and very simple oxidation problems. It also preserves the taste of the food itself and also makes the nutrients of the things well maintained.
Secondly, the product after boring does not lose the original skeleton structure, and can adhere to the original shape of the data to the greatest extent.
Once again, the food processed by the cold-drying processing technique has a porous structure, so it has a good rehydration property, and the speed of its dissolution in water is also very fast. In this case, the freshness of the food is also well protected. .
The fourth is to allow the water-soluble substances to be smoothly precipitated in the progress process. This is also useful to prevent other boring methods. Because the moisture inside the material is transferred to the surface of the material, many nutrients and inorganic salts are lost, which can be maximized. Adhere to the nutrients of the substance.
The final point is that the freeze-dried food is vacuum or nitrogen-packed in the process of production. It can also be stored in the dark, so the shelf life of these substances can last up to five years, compared with frozen food. Need to transport storage, this processing method can be very useful to improve the quality of the product.
(3) Control factors of vacuum freeze drying skills in food processing
(1) Pre-cooling rate and pre-cooling end temperature.
1 Pre-cooling rate optimization The freezing process will occur ice crystals of different particle sizes and directly affect the progress of boring speed. Some scholars have found that most of the fruit and vegetable materials attributed to blocks, strips and flakes are in the traditional slow freeze-drying process. The quality of the food produced under the condition is degraded, and the food made under the vacuum freeze-drying process condition can adhere to the original quality at all, and the practice indicates the appropriate freezing method. The pre-freezing pre-freezing rate does not affect the quality of the product. It can also speed up the boring rate.
2 Pre-freezing tail temperature optimization Freeze-dried food When the boring progress, the material has some liquid, will be agile under vacuum, form liquid concentration, nutrient components are lost, and the product volume is reduced. Therefore, the temperature of the pre-freezing tail is generally lower than the temperature of the eutectic point of the material (the temperature of the frozen water in the food guess) can be determined by the electric resistance method. The pre-freezing temperature can prevent the freezing temperature from being too low or too high to form the freezing energy. Excessive consumption or affecting the quality of production, generally required to be lower than the material eutectic point temperature of 5 ° C to 10 ° C or so.
(2) Heating method and temperature.
Most food lyophilization uses radiant heating. This method places the tray containing the material in the middle of the two radiant heating plates. The heat is transferred to the material by the upper and lower heating plates (separators), and the heating temperature ( Separator temperature) It is necessary to maintain the material ice layer beyond the inflection point during the progress of moisture (the food that is completely frozen, when the temperature rises to a certain point, the temperature point at which the ice crystal melts begins to be measured, and the maximum limit can be determined by the electric resistance method. Otherwise, it will seriously affect the lyophilization process and the quality and appearance of freeze-dried food.
Therefore, under the specific heat transfer method, the progress of the boring process and the desorption process, as long as the reasonable heating temperature is selected, the boring time can be shortened, the boring efficiency can be improved, and then the energy consumption can be reduced under the premise of ensuring the mass quality.