Relationship between physicochemical properties of blueberry fruit and cooling characteristics in freezing process
In the freeze drying of blueberry fruit, the prior freezing process is important to go forward with the drying operation smoothly. The prior freezing influences the total drying time, product quality and specific energy costs. Research on the freezing characteristics of blueberry fruit was carried out with samples of cultivar Tifblue, harvested in the farm of Tokyo University of Agricultural University, Japan. Material temperature in the central fruit was measured during the cooling experiment by using a temperature changeable deep freezer. The cooling characteristic curve was divided into three stages: liquid cooling stage, icing stage and solid cooling stage, to analyse cooling feature of blueberry. In the liquid cooling stage, material temperature of liquid phase decreases from the initial temperature to the icing temperature. In the icing stage, material becomes solid forming ice crystal and material temperature is nearly constant. In the solid cooling stage, material temperature of solid phase decreases from icing temperature to the set temperature of the freezer. In the result of experiment, the thermal diffusivities of blueberry in liquid phase and solid phase were computed from the experimental data by fitting the spherical heat transfer model. The effects of physicochemical properties such as fruit size and mass on the icing time and thermal diffusivities of blueberry in liquid and solid phase were clarified with the relation of the cooling temperature.
Ngo, Thi Hien, Tojo, S., Chosa, T. and Ban, T. (2018). Relationship between physicochemical properties of blueberry fruit and cooling characteristics in freezing process. Acta Hortic. 1213, 357-364
blueberry, freezing, thermal diffusivity