Abstract
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.