A histological study of pieces of meat frozen under controlled conditions which simulate the operation of industrial freezers, showed differences in the ice morphology according to the registered thermal histories.The diameter of the intracellular dendrites and extracellular ice crystals has been expressed mathematically in terms of a characteristic freezing time, while the percentage of the tissue water that was frozen and the variation of the ice-fibre interfacial area have been measured from the micrographs of transverse sections of frozen beef.

No abstract

The kinetics of starch gelatinization in potatoes was determined by a dynamic DSC method. The results were verified by an isothermal method. Experiments were carried out on small portions of potato tissue, thus assuring that the gelatinization conditions obtained were representative of the sum of the processes occurring on thermal treatment of potatoes. The rate constants were calculated and two activation energies were found for different temperature ranges. At temperatures below 67.5"C gelatinization was not complete, even for long reaction times. A reaction mechanism is proposed, assuming a semi-cooperative process where the gelatinization of the amorphous regions of the granule acts as a reaction "promoter" of the crystalline zones.

Experiments on thin-layer drying of wheat were interpreted in terms of a kinetic model based on internal control for water transfer and absence of temperature gradients inside the kernel. The drying operation in a batch fluidized bed was modelled by assuming a perfect mixing of solids. The kinetic parameters obtained from the thin-layer runs introduced into this model allowed to interpret satisfactorily drying experiments performed in a batch fluidized bed. Predictions of the model showed that drying times could be decreased about four fold by raising the air temperature from 40°C to 70°C. It was also calculated that inlet air temperatures much higher than that of wheat damage could be used without deterioration of grains during drying. Predicted thermal efficiencies were low suggesting the recirculation of air as a means of improving them.