Application of drying technology in processing of dehydrated vegetables

Most of the dehydrated vegetables produced in China are made by sun drying and hot air drying.
Because of the high temperature of sun drying and hot air drying, it is easy to produce quality problems such as color browning, loss of nutrients and poor rehydration performance. In China, a few enterprises adopt freeze-sublimation microwave drying machine technology, and the dehydrated vegetables processed are of good quality.
1 principles and characteristics
2.1 fundamentals of microwave drying
The water in vegetables exists in three different states: free water, colloidal bound water and combined water. Most of the free water and colloid bound water are removed during the drying process, and the hydrated water can not be removed by drying. The evaporation rate of moisture in vegetables is slower, not entirely depending on the temperature of dry air, but on the humidity saturation difference of air at this temperature, that is, the relative humidity of air, the lower the relative humidity, the faster the evaporation rate of moisture.


Microwave is a kind of thermal energy device which can absorb heat from low temperature heat source and make it be used effectively and controlled as useful heat at higher temperature. Microwave dryer consists of compressor, fan, condenser, evaporator, expansion valve, drying chamber and other parts. The principle of microwave drying is that the wet air first contacts the evaporator, and the moisture in the air cools down to the dew point and condenses. After dehumidification, the air flows forward to the condenser, absorbs the heat emitted by the condenser to make it warm up, and becomes the drying medium with high moisture loading capacity. Then the air blower blows back to the drying chamber and convects with the material to realize the material convection. Dry.

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