Abstract: The effects of immersion freezing and air freezing at different temperatures (-18 and -38 ℃) on the quality of braised beef with potato were studied by physicochemical measurements, microstructural observation and sensory evaluation. The results showed that freezing at -38 ℃ maintained better quality of braised beef with potato compared with freezing at -18 ℃, and immersion freezing was significantly superior to air freezing. The freezing time of beef and potato in the dish under -38 ℃ immersion freezing was shortened by 96.02% and 97.34%, respectively, compared with air freezing at -18 ℃, and the time required to pass through the maximum ice crystal formation zone for beef and potato was 9.67 and 10.92 min, respectively, suggesting improved freezing rate of the dish. Under this condition, the L*, a* and b* values of beef and potato were closer to those of the unfrozen dish; the hardness and elasticity of beef were significantly higher than those of the other frozen treatment groups (P < 0.05), and the shear force was 25.35 N, which was closer to that of the unfrozen sample (26.70 N), indicating good toughness of beef; the hardness of potato was 341.95 g, which was significantly higher than that of (P < 0.05) air-frozen samples, indicating good texture. Scanning electron microscopy (SEM) showed that beef muscle fibers were not broken after immersion freezing at -38 ℃, the gap between muscle fiber bundles was the smallest, arranged in an orderly manner; the cell contour of potato was clear and compact. The overall sensory score of the immersion-frozen sample was higher than that of the air-frozen one, and the sensory scores of beef and potato in the dish after -38 ℃ immersion freezing were 88.80 and 86.80 points, respectively, indicating higher acceptability. These findings provide a theoretical basis for the development of freezing preservation technologies for industrialized Chinese dishes.

Key words: braised beef with potatoes; air freezing; immersion freezing; dish quality