A theoretical approach was used to predict the water activity (a,) at 15°C and 35°C of selected saturated salt solutions used as standards in the range of microbial growth (20.57-0.97).For this purpose a rigorous thermodynamic model to predict osmotic coefficient was used. The results agreed very well with experimental measurements at 15°C and 35°C for most salts studied, which included NaBr, NaCl, (NH&S04, KCl, BaC12, and KzS04. For KNOs the agreement at the higher temperature was somewhat less satisfactory and the reasons for this behavior are discussed.
The drying behaviour of soybeans previously water soaked to a moisture content above that of the naturally moist product was studied. A comparison was performed between thin layer and fluidized bed drying (up to 20 cm depth). In both cases, thin layer or fluidized beds of variable heights, a satisfactory description of the drying kinetics was obtained using Fick's second law for diffusion out of spheres. However, it was found that the diffusion coefficients so obtained showed a tendency to decrease with increasing bed height. This is attributed to the drop in the temperature in the fluidized bed which affects the diffusion coefficients. Activation energies were found to be fairly independent of bed height and were in the range 6.9-7.4 Kcal/mol.
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