PILOT AND ANALYTICAL STUDY OF PROCESSES OF LOW-TEMPERATURE TREATMENT OF VEGETABLES
Low-temperature processing as a way of long storage of vegetable raw materials is the most widespread and economic allowing reducing the losses of raw materials, to keep consumer proper-ties and the quality of production. The following processes of low-temperature processing of the mixed vegetables packed in the package of a por-tion were investigated: convection freezing in the stream of ascending air on the metal gauze, con-ductive freezing on metal plate and combined way having the advantages of the first two ways. The combined way allows avoiding freezing of the package with the product to metal plate at the ex-pense of preliminary freezing on the grid in the stream of the ascending air. Freezing allows to re-ceive the frozen layer 2-3 mm thick on the product surface, and also to remove free moisture from packing surface. Temperature conditions of low-temperature processing: at - 30 °C and at -40 °C in a refrigerator chamber. The duration of freezing and the speed of each of processes were defined, thus freezing lasted before the achievement in the center of the product the temperature of -22 °C as at the achievement of this temperature in mix all free moisture crystallizes. The schedules of change of temperature in the thermal center of the product and on its surface are constructed during freezing. It is established that the most acceptable way is combined as the speed of freezing is high and as there is no damage of packing at separation of the frozen portion from the plate. The thermal calcula-tion of the combined way allowing determining the thickness of the layers which froze in the stream of air and owing to warmth return to metal plate with high precision is offered. The freezing duration re-ceived during thermal calculation completely coin-cides with experimental data that testifies about adequacy of the applied technique.