The account of water activity in the calculation of the rate of food product shrinkage

Refrigiration treatment and storing of the food product involves its mass loss due to its drying. The loss of mass and quality of food products is determined by ambient temperature and moisture parameters and water activity of the product itself. The use of existing formulas for calculating heat and mass exchange processes of refrigeration treatment and storage of food product is limited, because they don’t lake into account water activity and its temperature dependence on this parameter. A formula has been obtained for calculating the rate of food product shrinkage, considering the hygrothermal and thermophysical properties of the product and the environment, as well as the conditions for heat and mass transfer. The technological parameter of "water activity", with the increase of which the rate of evaporation of moisture from the product surface increases linearly, has been account in this formula. For determining dependence of food product water activity on temperature range within negative meaning it is suggested to use an analogue of tissue moisture possessing properties of diluted molecular solution. A criterion adequacy behavior of tissue moisture of food product and its analogue may be the share of frozen water. As analogue of tissue juice of food products the water solution of ethyl alcohol with mass concentration of 0.025 and temperature of freezing beginning 1(C is taken. Satisfactory results of comparing calculated and experimental data for temperature range of (1…34)(C have been obtained, which corresponds to industrial modes of buck food products refrigeration processes. Within this temperature range the water activity of water solution of ethyl alcohol drops with the temperature lowering from 0.990 to 0.748, in average amounts to water activity decrease of 0.007 to each degree of temperature drop.