Effect of supercooled freezing methods on ice structure observed by X-ray CT.

Because the quality of frozen food depends on the size of ice crystals, many studies have investigated the growth mechanisms of ice crystals in frozen foods. Recently, we developed a novel freezing called the freezing method to better understand the detailed mechanisms for the growth of ice crystals. In this study, X-ray micro tomography was used to investigate the 3D structures of ice crystals in soybean curds that were frozen by the supercooled freezing (Skyscan1172, Bruker microCT, Belgium). The 3D ice crystal structure produced by the conventional freezing was also measured for comparison. In addition, the 3D structure of ice that occurred at different degree of supercooling was also investigated. The results revealed that the conventional freezing formed cylindrical ice crystals and inhomogeneous configurations, whereas a high degree of supercooling created spherical ice crystals and relatively homogenous configurations. Further, a higher degree of supercooling produced more spherical ice crystals at a lower volume rate. Therefore, the supercooled freezing methods produced similar homogenous ice formation in the 3D structure to that previously found during experiments with pressure-shift freezing.