Effects of cooling step and static magnetic field on the freezing characteristics of apple

Many technological approaches have been explored to improve the quality of frozen food. The present study aimed to investigate the influence of cooling steps and magnetic field on the freezing characteristics of apple tissue. The apple samples were cut into (24 mm × 24 mm × 24 mm) cubes and subjected to freezing under different cooling steps and magnetic field intensities (41.35 mT, 68.81 mT, 90.3 mT, 105.33 mT). The variations in temperature during freezing, as well as weight loss, tissue hardness, and microscopic structure after freezing and thawing of apple samples, were recorded. The results showed that phase transition first occurs in regions with a large temperature gradient. Both the cooling rate and temperature uniformity of the sample should therefore be considered synthetically when optimizing the freezing effect. Moreover, the magnetic field elevated the phase transition temperature of apple tissues and prolonged the freezing duration, thereby exacerbating structural damage to cellular architecture during cryopreservation. These findings provide valuable references for the corresponding theoretical research and device design of magnetic field-assisted cryogenic extraction.