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 l evels (100, 150 and 200 MPa). Temperature and pressure profiles were compar ed and the maximum supercooling obtained after pressure release was evaluat ed. A comparison between the freezing steps at atmospheric pressure and tho se of pressure-shift freezing was carried out to compare the time steps dur ing the processes. The degree of supercooling increased with the level of p ressure. For pressure-shift freezing, the size of ice crystals appeared to be more homogeneous in the whole sample and independent of the location. Th e mean representative ice crystal diameter decreased as the pressure level increased. This may be due to the degree of supercooling achieved during pr essure-shift freezing. The ice crystal size for pressure-shift frozen sampl e was smaller than those obtained with classical freezing methods. A regres sion between the supercooling level and the mean ice crystal size was propo sed. (C) 2000 Elsevier Science Ltd. All rights reserved.