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Establishment of systematic data of thawing times regarding pressure-induced and pressure-assisted thawing of model foods and real products

Pressure–assisted (PAT) and pressure–induced thawing (PIT) experiments were performed in agar gel at pressures 50 to 210 MPa and initial temperatures –5 to –20°C. Lower pressures and temperatures yielded PAT processes in which the sample temperature increases during pressurization: no melting took place. The complete phase transition occurred during the holding time.

Higher temperatures and/or higher pressures yielded PIT processes in which partial melting occurred during pressurization, causing decrease of the temperature. Obtaining PAT or PIT depends on the initial temperature of the sample for a given pressure. Common situations were non homogeneous thawing processes.

The influence of pressure, individually considering the temperature gradients and latent heats of fusion existing at different pressure levels was studied. New processes, as thawing from pressures in the domain of ice III and ice V or pressure-shift thawing have to be considered in the future, when industrially implementing thawing processes.

The existence of extended lines of the melting curves of ice I and ice V and the subsequent existence of metastable phases of ice I and ice V in the domain of ice III are proven. The physical phenomena occurring during thawing are explained through schematic representations of the sample cylinders.

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Berlin University of Technology
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