Influence of the pressure shift freezing and thawing on the microstructure of largemouth bass

The objective of this study was to use a new self-cooling laboratory system for carrying out the pressure shift freezing (PSF) and evaluate the influence of PSF at 150 MPa on the microstructural properties of largemouth bass relative to liquid immersion freezing (LIF) and conventional air freezing (CAF). CAF, LIF and PSF showed average total freezing times of 176 ± 7.4, 65.3 ± 6.8 and 23.2 ± 3.1 min, and the cross sectional area of ice crystals in the muscle were 1002 ± 778, 501 ± 248 and 143 ± 50.6 μm2, respectively, demonstrating a significant reduction in crystal size to be associated with PSF. It was observed that damage caused by the ice crystals during the freezing to the muscle microstructure was irreversible. The thawing and cooking losses of largemouth bass after the freezing were lower for PSF as compared to the other two freezing methods. PSF reduced the damage to myocytes and resulted in lower drip loss due to reduced microstructure disruption due to their small ice crystals, thereby maintaining the muscle tissue to better retain the fluids. Color and texture properties were less affected by PSF. Freezing is the most used preservation method for aquatic products. Rapid freezing results in better texture retention while the slow freezing damages the product texture because of the formation of extracellular large ice crystals developed during the freezing process. Thus, the nature of freezing affects the quality of frozen foods. Successful freezing processes aim at employing rapid freezing conditions which result in the formation of small ice crystals. Pressure shift freezing (PSF) is a novel technique with advantages of high degree of super-cooling, short phase transformation time, and results in very small ice crystals. This study makes use of a laboratory self-cooling system to carryout PSF of largemouth bass. This cooling system overcomes the limitation of previous studies on PSF which are expensive, limited to small size and impractical for commercial exploitations. The cooling system employed in this study can be easily adapted to large-scale production of PSF aquatic products. Test results provide a basis for the commercial exploitation of PSF for largemouth bass and such other aquatic foods for driving the quality advantage.