The Choice of the Parameters of Vacuum Freeze Drying to Thermolabile Materials with Desired Quality Level

摘要

Vacuum freeze drying is considered to be the most effective technique to preserve the native properties of objects to be dried. Despite the fact that freeze drying is related to high energy consumption and sophisticated equipment. However, the possibility to change the situation is far from exhausted. The research is devoted to perspective ways for increasing energy efficiency in freeze drying and obtaining a final product with a desired level of quality. The process of freeze drying of the fruit raw material at the temperature of phase converting ice-to-vapour (-10 C-35 C below zero), at an appropriate vacuum level and different operating condition of freezing machines and vacuum pumps has been analyzed. As an example, the change in ascorbic acid content at different drying process parameters has been measured. Main patterns of interrelationship between process parameters and the quality of final product were determined with the use of commercial freeze dryer UVS-80M. It suggested overall quantitative evaluation of quality of the dried product considering time and the degree of heat effect on raw material. During the freeze drying of apples (Malus pumila "Antonovka") we obtained data showing that the use of lower primary drying temperatures results in better quality of frozen fruit but the duration of freeze drying process increases along with energy consumption The article describes the means of decreasing the specific energy consumption involved in the vacuum freeze-drying by adapting the design of freeze drying machines and their operating modes to the level of quality required by customer.