Developing and validating a model food using gelatin gel for liquid nitrogen spray freezing of Larimichthys crocea: Thermal properties, freezing characteristics, and microstructure

To develop a model food for the large yellow croaker (LYC, Larimichthys crocea) muscle subjected to liquid nitrogen spray freezing (LNSF), the effects of temperature and concentrations of gelatin (5%, 10%, and 15%, w/w), sodium chloride (0%, 3%, 6%, and 9%), and sucrose (0%, 3%, 6%, and 9%) on thermal properties of frozen gelatin gels were investigated. Thermal conductivity (k) and diffusivity (α) significantly decreased (P < 0.05) with increasing gelatin concentration and decreasing sodium chloride content. Adding sucrose significantly decreased k but raised α. Increasing the concentrations of all three components reduced the volumetric heat capacity (C_pV). The gelatin gel with 16 % gelatin and 4 % sucrose was selected as the model food because its thermal properties most closely matched those of LYC muscle. At depths of 5, 15, and 25 mm, the total LNSF freezing durations for gels (164.78, 167.01, and 167.40 min) were similar to those for fish muscles (167.67, 169.47, and 168.93 min), validating that the developed model food effectively simulated the freezing characteristics of real food. The significant decrease in cross-sectional area from 1538.63 to 850.90 μm² and area uniformity index from 2.507 to 1.612 with decreasing freezing temperature from −20 to −100 °C demonstrated that rapid freezing generated uniformly distributed fine ice crystals. This phenomenon indicated that the model food could simulate the quality changes in fish muscle with LNSF freezing temperature. In summary, adjusting the component content of gelatin gels can be used to develop model foods for aquatic products to optimize LNSF freezing protocols.