Water phase transition under pressure and its application in high pressure thawing of agar gel and fish

• We get the phase transition temperatures of water in salmon and agar gel under high pressure.
• Phase transition temperature of water in salmon is significantly lower than that of pure water.
• The temperature of melting plateau for frozen salmon appears an increasing trend under high pressure.
• HP causes a depression of the ice-melting temperature, significantly accelerated the thawing process.
• We calculate the time of thawing under pressure for frozen agar gel and salmon.

Experiments were carried out with a high-pressure (HP) differential scanning calorimeter (DSC) and a HP unit using frozen agar gel (3%, w/w) and Atlantic salmon (Salmo salar). Small samples (0.54–0.7 g) were prepared for HP DSC tests. Frozen samples of agar gel and salmon muscle in cylinders (47.5 mm diameter, 135 mm length) were subjected to water immersion thawing (WIT) (20 °C) and HP thawing at 100, 150 and 200 MPa with a water temperature of 20 °C. Phase transition temperature of agar gel was close to the phase diagram of pure water. Melting temperature of salmon was significantly lower than phase diagram of pure water probably due to the presence of solutes and cellular structures in fish. HP DSC tests demonstrated a good correlation between temperature (T) and average pressure (P): T = −1.22–0.0946P − 0.000115P2 (R2 = 0.99, n = 10). High pressure caused a depression of the ice-melting temperature resulting in an accelerated thawing process. The reduction of melting plateau time can be predicated by using Plank’s model. For frozen agar gel, the total thawing time was 50.3 ± 2.7, 36.4 ± 2.2 and 30.8 ± 1.8 min, or 73, 53 and 45% of WIT time (68.7 ± 4.3 min) at 100, 150 and 200 MPa, respectively. For frozen fish, the total thawing time was 58.9 ± 2.8, 41.8 ± 4.7, 37.2 ± 2.6 and 33.8 ± 1.9 min for WIT, HPT at above pressures, respectively.