Porosity and density of abalone, potato, apple, and two varieties of dates were investigated as a function of shelf temperature during freeze-drying. The pore formation in food materials showed two distinct trends when shelf temperatures were maintained at constant level between -45 to 15°C. The materials in a group I (i.e., abalone, potato, and brown date) showed a decreasing trend, whereas in the group II (i.e., apple and yellow date) showed an increasing trend in pore formation. The results found in this study could not be explained alone by the glass transition concept.
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