Calculation of food product drying speed depending on water activity in the refrigeration processes

For citation: Erlikhman V.N., Fatykhov J.A. Calculation of food product drying speed depending on water activity in the refrigeration processes. Vestnik Mezhdunarodnoi akademii kholoda. 2018. No 4. p.10-14.

Abstract
In the processes of refrigeration the losses of food product mass is determined by temperature and moisture parameters of ambient environment and water activity of the product. The formulae for calculating mass exchanging processes in use do not take into account temperature dependence of water activity. The authors suggest using the expression which was been obtained earlier for determining speed of water evaporation from food product at different temperatures taking into account gigrothermal parameters of ambient environment, the intensiveness of thermal–mass exchange and water activity. To determine the dependence of food product water activity on the negative temperature range it is suggested to use an analogue of tissue moisture with the properties similar to the ones of diluted molecular solution. The share of frozen water can be chosen as a adequacy criterion for t tissue moisture of food product and its analogue. As an analogue of tissue juice of food products the water solution of ethyl alcohol with mass concentration of 0.025 and freezing onset temperature of –1°C is taken. The results of calculation for freezing temperature lowering and the share of frozen water for water solutions of ethyl alcohol with different concentration and their comparison with the experimental data are presented. Satisfactory results of calculated and experimental data comparison for the temperature range of (–1…–34)°C have been obtained, which corresponds to the industrial modes for refrigeration processes of food products. Within this temperature range the water activity of ethyl alcohol water solution drops with the temperature lowering from 0.990 to 0.748, that on the average amounts to water activity decrease of 0.007 to each degree of temperature drop. The data presented can be used as a calculation method to determine food products drying depending on water activity calculated by an analogue product tissue moisture within the range of industrial temperatures of refrigeration.