Pressure‐shift freezing and its influence on texture, colour, microstructure and rehydration behaviour of potato cubes

Temperature changes during pressure‐shift freezing (400 MPa) of potato cubes and its effects on the drip loss (weight and conductivity), texture (shear and compression tests), colour (L, a, b values), drying behaviour, rehydration properties (water uptake, texture after rehydration) and visible cell damage after thawing (micrographs) were investigated and compared with conventional freezing (0.1 MPa, ‐30 °C), subsequent frozen storage (‐18 °C) or pressure treatment (400 MPa) at +15 :C. Pressure‐shift freezing resulted in increased crystallization rates compared to conventional freezing at ‐30 °C. Crystallization and cooling to −8 =C took 2.5 min during and after pressure release versus 17 min at atmospheric pressure. Drip loss was reduced from 12.0 to 10.8g/100g. Water uptake during 10 min of rehydration (93.9g/100g compared to 77.4g/100g and incomplete rehydration) and texture values were improved. Browning after thawing or after fluidized bed drying was reduced (increased a value, lower L value), suggesting partial enzyme inactivation during pressure treatment. Differences in colour and texture to the untreated controls were smaller after pressure‐shift freezing than after conventional freezing. Cooling to −30 °C after pressure‐shift freezing did not significantly affect the results, whereas subsequent frozen storage at −18 °C resulted in quality deterioration, as observed after frozen storage of conventionally frozen samples. The improved preservation of cell structure was demonstrated using scanning electron microscopy.