PRESSURE-SHIFT FREEZING AND ITS INFLUENCE ON TEXTURE, COLOR, MICROSTRUCTURE AND REHYDRATION BEHAVIOR OF POTATO CUBES

Temperature changes during pressure-shift breezing (400 MPa) of potato cubes and its effects on the drip loss (weight and conductivity), tex ture (shear and compression tests), colour (L, a, b values), drying be haviour, rehydration properties (water uptake, texture after rehydrati on) and visible cell damage after thawing (micrographs) were investiga ted and compared with conventional freezing (O.1 MPa, -30 degrees C), subsequent frozen storage (-18 degrees C) or pressure treatment (400 M Pa) at +15 degrees C. Pressure-shift freezing resulted in increased cr ystallization rates compared to conventional freezing at -30 degrees C . Crystallization and cooling to -8 degrees C took 2.5 min during and after pressure release versus 17 min at atmospheric pressure. Drip los s was reduced from 12.0 to 10.8 g/100 g. Water uptake during 10 min of rehydration (93.9 g/100 g compared to 77.4 g/100 g and incomplete reh ydration) and texture values were improved. Browning after thawing or after fluidized bad drying was reduced (increased a value, lower L val ue), suggesting partial enzyme inactivation during pressure treatment. Differences in colour and texture to the untreated controls were smal ler after pressure-shift freezing than after conventional freezing. Co oling to -30 degrees C after pressure-shift freezing did not significa ntly affect the results, whereas subsequent frozen storage at -18 degr ees C resulted in quality deterioration, as observed after frozen stor age of conventionally frozen samples. The improved preservation of cel l structure was demonstrated using scanning electron microscopy.