Wspólnotowy Serwis Informacyjny Badan i Rozwoju - CORDIS

Mathematical modelling of pressure-supported freezing and thawing processes

Good predictions of plateau times can be made from initial pressure and temperature values, both process parameters that can be readily adjusted in the food industry. Potato phase diagram has been experimentally obtained. The results have been used to define new concepts and processes, like ¿areas of nucleation¿ and ¿metastable phases¿.

It can be observed that the phase transition line of ice I presents an extension in the domain of ice III, as well as for ice V in the domain of ice III. The degree of supercooling is clearly higher for ice III than for ice I and the distribution of the points obtained led to the definition of ¿areas of nucleation¿ as a better term than ¿nucleation lines¿. The existence of phase transition and nucleation points of both ice I and ice V into the domain of ice III led to the definition of ¿metastable phases¿. The water phase during the time at which the sample temperature remains below the phase transition point without nucleation must be also considered as a liquid metastable phase.

The existence of these metastable phases opened new processing opportunities, especially for pressure-shift freezing and pressure-induced thawing, to optimise the thermal gradients (therefore increasing the amount of instantaneously frozen ice during pressure-shift freezing and reducing the processing time for pressure-induced thawing). Freezing, thawing, phase transition times have been defined. A bench-mark test in the equipment of three different laboratories was performed: a HPLT laboratory vessel placed in Berlin (TUBER), a HP pilot plant placed in Madrid (CSIC-1), a HP laboratory vessel also placed in Madrid (CSIC-2) and a HP vessel placed in Nantes (ENITIAA). Two different processes were carried out, PSF at 200 MPa and PIT at 200 MPa and the processing times were recorded.

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