The effect of cooling rates on the ice crystal growth in air-packed salmon fillets during superchilling and superchilled storage

Salmon fillets were superchilled in an impingement freezer using four different treatments, A (heat transfer coefficient 153 W m−2 K−1, air temperature −20 °C), B (227 W m−2 K−1, −20 °C), C (153 W m−2 K−1, −30 °C) and D (227 W m−2 K−1, −30 °C), and stored at −1.7 °C for 28 days. The influence of these treatments on the microstructure of salmon fillets was studied. The equivalent diameter of the intracellular ice crystals formed were 124 ± 14, 110 ± 4, 114 ± 16, and 95 ± 5 μm for the samples subjected to treatments A, B, C and D, respectively, after one day of storage. Smaller size of the ice crystals were observed in fillets superchilled using treatment D compared with other treatments. Significant differences were observed between the size of ice crystals formed during the superchilling process and superchilled storage. The results further indicated that, the growth of the intracellular ice crystal was significant at (P < 0.05) for the entire storage time. However, after temperature equalization (1 day of storage), there was gradually growth of the intracellular ice crystals compared to that observed before temperature equalization (i.e. day 0 and 1). Conversely, spurt growth of the size of ice crystals were observed between 14 and 21 days of storage.