Influence of Pressure-assisted Freezing on the Structure, Hydration and Mechanical Properties of a Protein Gel

摘要

Due to renewed interest in high pressure technology (2), the phase diagram of water under pressure (1) has been reexamined in view of potential food applications (4,8). Since water remains liquid until -22 deg C at a pressure of 207,5 MPa, pressure-shift freezing, pressure-assisted thawing and non frozen storage under pressure are all possible in the 0 to -22 deg C rang. For pressure-shift freezing, a biological sample is cooled under pressure to a temperature just above the melting temperature of ice at this pressure. Upon sudden pressure release, supercooling of water present in the sample enhances heterogeneous ice nucleation (12), inducing the formation of a large number of small stable ice nuclei. These give rise, after crystal growth, to a large number of small ice crystals, thus avoiding the damage to tissue and cell structures caused by large crystals with resulting drip and altered texture after thawing. Pressure-shift freezing may also lead to a uniform size distribution of ice crystals throughout the sample, since the initial supercooling is quasi-uniform throughout sample depth. To maintain these advantages, however, the latent heat of crystallization should be removed quickly, and this requires a low temperature or a stirred cooling medium and/or a small sample size. Low temperature frozen storage would be mandatory, to avoid ice recrystallization.