Dynamics of changes in the thermophysical characteristics of fruits and berries during freeze-drying

Knowledge of thermophysical properties is nec-essary in the calculation of technological process-es, accompanied by changes in the temperature of the object in time but also in the design and selec-tion of appropriate equipment. The aim of this work was to study dynamics of thermal properties of fruit and berries in the freeze-drying process. As objects of the study were selected shadberry, honeysuckle and cowberry. Thermophysical properties such as heat capacity, temperature and thermal conductivi-ty, and density at various moisture contents in the product were determined by calculation. For fresh frozen fruit and berries at the initial stage of freeze-drying density to saskatoon, cranberry and honey-suckle it was 982, 984 and 911 kg/m3 respectively. By the end of the sublimation drying, the density of the berries decreased to honeysuckle, amelanchier, and cranberries in 47, 34 and 22 %, respectively. There was a linear relationship between heat ca-pacity and moisture content of the product. The magnitude of the heat capacity of frozen and dried fruits and berries was in the intervals 2032÷ 2144 kJ/(kg•K) and 1123÷1141 kJ/(kg•K). The thermal conductivity of frozen wild berries amount-ed to 1.90÷1.97 W/(m•K) for honeysuckle and cowberry and 1.70 W/(m•K) for Saskatoon. When freeze-dried to achieve moisture content of 5% the thermal conductivity of dehydrated berries was in the range of 0.156÷0.162 W/(m•K). For cranberries and saskatoon the highest conductivity was ob-served at the initial stage of drying when the great-est moisture content and was (9.04÷9.84)• 10-7 m2/s. as for the berries of the honeysuckle, the maximum of the thermal conductivity when the moisture content of about 60% to 10,57 •10-7 m2/s. According to the obtained dependencies of thermal properties on moisture content were obtained from the regression equation.