Process flow of freeze-dried fruits and vegetables
Selection of raw materials, pre-freezing, sublimation, drying, packaging and storage.
Operation points of freeze-dried fruits and vegetables
(1) Pretreatment of freeze-dried fruits and vegetables.
Generally. pretreatment refers to all treatments before sublimation drying, so freezing before drying also belongs to pretreatment. Raw material pretreatment and conventional fruit and vegetable drying and frozen products are the same, such as selection, cleaning, peeling, cutting, blanching, cooling and other processing, not detailed here. When fruit or vegetable juices are freeze-dried, they are pre-concentrated using cheaper processing methods and then granular when pre-frozen.
Pre freezing is to freeze the raw materials after the pre-treatment, which is an important process of lyophilization. Due to a series of complex biochemical and physicochemical changes in frozen fruits and vegetables, the quality of freeze-dried fruits and vegetables will be directly affected by the quality of pre-freezing. During the freezing process, the effect of the freezing rate on the quality and drying time of the frozen material is mainly considered.
The differences between quick freezing and slow freezing are as follows: the ice crystals produced by quick freezing are smaller, while the ice crystals produced by slow freezing are larger. Large ice crystals are favorable to sublimation while small ice crystals are unfavorable to sublimation. Small ice crystals have less effect on cells. The smaller the ice crystals are, the more they can reflect the original structure and properties of the product after drying. But the freezing rate is high and the energy consumption is high. An optimal freezing rate should be selected to ensure the quality of freeze-dried food and minimize the freezing energy consumption.
