欢迎来到Changzhou Qiangdi drying equipment co., LTD.官方网站

Vacuum drying equipment for food and its progress

Tags:Vacuum dryer, drying equipment, dryer
  Air drying has been widely used in the food industry. In the past few years, the vacuum technology, microwave heating and other drying technologies have been combined, and some new types of vacuum drying devices have emerged, and a new point of view on the development and development of vacuum microwave drying devices in China is proposed.
0. preface, an important trend in the development of food processing technology is to maintain the nutrition and color aroma of food to the maximum, and the selection of drying technology and equipment has a great influence on the nutrition and color aroma of food products. Food drying has many characteristics associated with "food". It is different from the drying of chemical products. The former needs to consider the food hygiene, the loss of nutrition, the change of color and fragrance, and so on. The drying temperature and time are strictly limited. The drying of food is different from the drying of medical products, because the food is often a low added value product. Drugs are generally high value-added products, and the former must consider the economy of the drying process. Around "quality and economy", some progress has been made in the drying technology and equipment of food in recent years, in which vacuum is combined with other drying methods or heating technology, which gives the new connotation and vitality of the vacuum drying device.
1.The characteristics of vacuum drying in food are based on this basic principle: the saturated vapor pressure of water is closely related to the temperature. In the vacuum state, the boiling point of water is reduced, that is to say, the operation of the water under the vacuum is also operated at low temperature. It can avoid the destruction of the nutrients, vitamins and so on at the high temperature, and improve the drying speed. In addition, in the vacuum system, the content of air in the unit volume is lower than that in the atmosphere. In this relatively anoxic environment, food drying can reduce or even avoid the opportunity for oxidation of fat in food, pigment browning or other oxidative deterioration, so the better quality of food can be obtained by vacuum drying.
2.Vacuum drying of traditional vacuum drying equipment is widely used in food, pharmaceutical, chemical industry and other industries. Various kinds of vacuum drying equipment have been developed and introduced in China. Commonly used forms in the food industry are box type, double cone vacuum dryer, belt vacuum dryer and so on. These traditional vacuum drying devices are mainly heated by hot air, steam or electricity, and use the principle of heat conduction, convection or radiation to transfer heat from the outside to the inside of the material.
2.1Box type vacuum dryer box vacuum drying is the oldest and the simplest kind of vacuum dryer. There are many hollow heating plates in the vacuum drying box. The heating plate is heated by steam. It can also be heated by electric heating or other radiation. The material is placed on the metal plate and placed on the heating plate. The heat reaches the interior of the material through heat conduction, so that the water is heated and evaporated. Box vacuum dryer is still widely used in practice, and it is suitable for drying liquid, paste, powder and granular food materials.
2.2A double cone vacuum dryer is a double cone vacuum dryer that turns a conical container with a symmetrical jacket. The material is constantly stirred by the inclination of the inner cone itself. Through the rotary joint, the steam or heating carrier is sent to the side of the rotating shaft, and the exhaust pipe with the filter net with the center of the other end is used. The double cone vacuum dryer can achieve higher vacuum degree, simple internal structure, easy cleaning, and all materials can be discharged.
2.3Vacuum belt dryer vacuum belt dryer is composed of a continuous stainless steel belt. The steel belt passes through the heating roller and the cooling roller. The structure is multi-layer, which forms the main body of the dryer, and then it is included in the closed vacuum chamber. The material book is flat on the belt type heating plate. Because the material is bubbling on the heating plate under the vacuum condition, the finished product has the porosity, the whole system is closed operation, the sanitary condition is good, the actual operation vacuum degree 100~10Kpa, the heating temperature is about 150 centigrade, and the conditions (drying temperature and time) Between freeze-drying and spray drying, the quality of the finished product is close to the freeze drying, but the freeze-drying is a clearance operation while the vacuum belt dryer is a continuous operation. It is especially suitable for the drying of heat sensitive and highly oxidizing foods. The liquid or pulp materials are well used. The dry orange juice, tomato juice, and the juice are used in food. Instant tea, etc.
2.4Vacuum drum dryer vacuum drum dryer is closed in the vacuum chamber. In the vacuum drum dryer, feed, discharge and scraping must be controlled from the dry outdoor, so the drying cost is very high, so it can only be used for the drying of very hot and sensitive food, if the juice, yeast, baby food and so on.
3. new development of vacuum drying equipment, the traditional vacuum drying devices are mostly heated by heat conduction, convection or heat radiation, and the heating speed is slow and not uniform. In recent years, the researchers combined vacuum technology with microwave heating technology and other drying technologies, and some new types of vacuum drying devices have emerged.
3.1Vacuum freeze-drying water has three aggregation states, namely liquid, solid state and vapor state. As the pressure continues to decrease, the freezing point changes little, while the boiling point is getting lower and closer to freezing point. When the pressure drops to a certain value, the boiling point is combined with the freezing point, and the solid ice can be directly converted to the vapor state without passing through the liquid state. The three-phase point pressure of water is 610.5Pa, the three phase point temperature is 0.0098 C. When the pressure is lower than the three phase pressure, the solid ice can absorb the heat directly into steam. The principle of freeze drying is the principle of this. When vacuum freeze-drying, the product is placed in a vacuum chamber, between two heating plates, using low temperature to excite far infrared heating to ensure that the drying is uniform. The temperature of the heating plate is precisely controlled according to the heating curve of the drying process. The selection of the vacuum degree should ensure that all the moisture in the whole drying process is insoluble in the form of ice. For most vegetables and meat, the selection of 0.5~1Pa, corresponding to the sublimation temperature around 25 degrees C, is suitable. Because the vacuum freeze-dried food is dehydrated at a very low temperature, the food has little loss of flavor and flavor, and it can retain the original nutrition and flavor to the maximum. The rehydration is excellent. It can be recovered within a few seconds to several minutes, and its color, taste and shape are the same as that of fresh products. Vacuum freeze-drying products are many: coffee, instant tea, fruit juice, herbal medicine, vegetables such as onion, garlic, ginger, mushroom, meat, shellfish and so on. Vacuum freeze-drying is a big investment, so many food manufacturers are prohibitive, such as the ATLAS RAY50 freeze-drying equipment in Denmark (the freeze-dried area 45m2) is up to 1 million 50 thousand dollars, the domestic freeze-drying machine just started, the quality and foreign products still have a big gap, in addition, the vacuum freeze-drying production costs are also higher, It is because of the need to maintain a high vacuum and (-25) low temperature, long drying time, high energy consumption, these factors make the use of frozen drying in the food industry to bring a lot of resistance.
3.2Jet continuous vacuum dryer is also called (Filtermat spray dryer).
  Spray continuous vacuum dryer, also known as Filtermat spray dryer, is equivalent to the combination of belt vacuum dryer and spray dryer.Niro
  HudsonThe desiccator developed by the company has successfully solved the drying problem of sticky food, such as high sugar content, high fat content or high acid content. The sticky material will stick to the wall phenomenon with the traditional spray dryer, and it is difficult to dry. During the drying process, the material is sprayed vertically down to the spray drying chamber through the pressure nozzle, and the hot air is also sprayed down. The semi dry powder material is gathered on the moving net belt, the tail gas is also discharged by the fan, and the dry material is further moved, cooled and collected on the net belt. Because of the medium vacuum in the spray tower, the hot air temperature is only about 100 C, and the general hot air temperature of the spray drying is about 150 degrees C, so the heat sensitive material is lost and the height of the spray tower is reduced.
3.4Microwave vacuum drying microwave is the wavelength 1.0~0.001m, the frequency is 300~300000MHz, has the penetrating electromagnetic radiation wave. The microwave drying principle is that microwave generator radiates the microwave to the dry material. When the microwave is injected into the material, the water and other polar molecules are rotated with the frequency of the microwave, for example, the drying of vegetables and vegetables. Using the microwave of 915MHz, the polar water molecules in the vegetables rotate 915 million times per second. The result of such high-speed rotation of water and other polar molecules makes the material produce friction heat instantaneously, which causes the surface and interior of the material to heat up at the same time, so that a large number of water molecules escape from the material to achieve the effect of material drying. The traditional heating methods, such as steam, hot air and electricity, use the principle of heat conduction, convection and radiation to transfer the heat from the outside to the inside of the material. It takes a certain amount of time from the exterior. The more time the thermal conductivity of the material is, the longer it takes, so the heating speed is slow, the heat is not uniform and the energy consumption is high. Microwave heating is the heating body itself, so it is called the heating body itself, so it is called the internal heating method, the microwave passes through the food in all directions, the food is heated at the same time both inside and outside, neither the heat transfer medium nor the convection is needed, the temperature of the food and outside is rising at the same time, the heating speed is fast and uniform, only a few points of the traditional heating method are needed. One or dozens of ingredients, and can better retain the original color and flavor of food and vitamins. The results showed that the chlorophyll, vitamin and other nutrients in the dried vegetables were only 3%, 17% in dry, 40% for hot air drying, and 60%~90% in microwave drying, and 97%{2} in vacuum freeze drying. Microwave vacuum drying is a very promising drying technology, which combines microwave technology and vacuum technology organically, giving full play to the fast and uniform microwave heating and the low vaporization point in the vacuum condition. Microwave vacuum drying technology in France, Japan and the United States has been promoted from laboratory to industrial production in recent years. This technology is very suitable for the deep processing of heat sensitive food.
The United States University of California, in cooperation with a company, uses microwave vacuum drying seedless raisin to keep the original shape and color of the grapes, avoiding the shortcomings of the past traditional technology (65 C hot air for 24 hours) and the change of color, shape, flavor and nutrients, and the quality of the products is greatly improved. The microwave vacuum dryer (2450MHz, 48Kw) made by France international microwave Co., Ltd. has a diameter of 1.5m, the length of 12M, and the processing of instant orange powder. The product not only keeps the original color, but the preservation of the vitamin is much higher than that of the spray drying. In recent years, the demand of high grade dehydrated vegetables at home and abroad is very large, and the production of dehydrated vegetables is the key to determine the quality of the products. The vacuum freeze-drying to prepare dehydrated vegetables is of high quality, but the vacuum freeze-drying equipment is expensive and the production cost is high. Since 80s, the vacuum microwave has been used in foreign countries. The production of dehydrated vegetables by hot air (45%~55%) is equivalent to the products produced by freeze-drying technology, with less investment in one time and a significant decrease in the total cost.
4.Concluding remarks
  Vacuum drying has a low drying temperature and relative hypoxia in the drying room. It can avoid a series of advantages, such as fat oxidation, pigment browning, and so on. It is suitable for the drying of thermosensitive food materials. In addition, the cost of equipment and the cost of drying are relatively low, and the vacuum drying has a important position in the middle of food drying.
  The combination of vacuum drying with microwave heating or other drying methods has brought up a number of new vacuum drying devices, which have given the new connotation and vitality of vacuum drying.
  Vacuum microwave drying absorbs the advantages of both microwave heating and vacuum drying. It is a promising drying technology. It is recommended to speed up the development and development of vacuum microwave drying equipment in China.
相关文章
Relevant Products
  • Horizontal disc dryer
    Horizontal disc dryer
  • SZG Series Double Cone Rotating Vacuum Dryer
    SZG Series Double Cone Rotating Vacuum Dryer
  • FZG/YZG Static Vacuum Dryer
    FZG/YZG Static Vacuum Dryer
  • ZPG vacuum rake dryer
    ZPG vacuum rake dryer
  • GFG series high efficiency boiling dryer
    GFG series high efficiency boiling dryer
  • XF Series Horizontal Fluidizing Dryer
    XF Series Horizontal Fluidizing Dryer
  • KJG hollow blade dryer
    KJG hollow blade dryer
  • ZLG series vibrating fluidized bed dryer
    ZLG series vibrating fluidized bed dryer
  • XSG rotary flash dryer
    XSG rotary flash dryer
  • PLG disc type continuous dryer
    PLG disc type continuous dryer