Mk. Krokida et al., EFFECT OF FREEZE-DRYING CONDITIONS ON SHRINKAGE AND POROSITY OF DEHYDRATED AGRICULTURAL PRODUCTS, Journal of food engineering, 35(4), 1998, pp. 369-380
Structural proper ties such as particle density bulk (or apparent ent)
density and porosity of apple, banana, carrot and potato were investi
gated after freeze-drying under various drying conditions. The materia
ls were freeze-dried at various pressures, to achieve sample temperatu
re ranging between -50 and -5 degrees C. Fbr temperatures above the gl
ass transition temperature of the concentrated amorphous solution (T'(
g)= -45 degrees C), the freeze-dried materials decreased in size. The
bulk density of the freeze-dried materials was increased with temperat
ure and an exponential equation was used to express this influence. Th
e final porosity decreased as the sample temperature increased for all
the materials examined, ranging between 70 and 95%. The final porosit
y was related to the complex viscosity of frozen apple and potato whic
h decreased linearly as the temperature increased in the temperature r
ange examined. (C) 1998 Elsevier Science Limited. All rights reserved.