Structural collapse of plant materials during freeze-drying

Structural collapse of plant materials, which affects quality of foods, was studied. Fresh and osmotically dehydrated plant materials were freeze-dried at several chamber pressures, to achieve initial sample temperatures that were below (-55 degrees C), near (-45 degrees C), or above (-28 degrees C) their glass transition temperature (T-g=45 degrees C). Freeze-drying at -55 degrees C resulted in products retaining their original volume. When the initial sample temperature was increased above T-g, the resulting freeze-dried samples collapsed. When the initial sample temperature was increased above the temperature of ice melting (T-m'), the samples collapsed further.