Freezing and ice crystals formed in a cylindrical food model: part II. Comparison between freezing at atmospheric pressure and pressure-shift freezing

Cylindrical gelatin gels were pressure-shift frozen at different pressure levels (100, 150 and 200 MPa). Temperature and pressure profiles were compared and the maximum supercooling obtained after pressure release was evaluated. A comparison between the freezing steps at atmospheric pressure and those of pressure-shift freezing was carried out to compare the time steps during the processes. The degree of supercooling increased with the level of pressure. For pressure-shift freezing, the size of ice crystals appeared to be more homogeneous in the whole sample and independent of the location. The mean representative ice crystal diameter decreased as the pressure level increased. This may be due to the degree of supercooling achieved during pressure-shift freezing. The ice crystal size for pressure-shift frozen sample was smaller than those obtained with classical freezing methods. A regression between the supercooling level and the mean ice crystal size was proposed. (C) 2000 Elsevier Science Ltd. All rights reserved.