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Keywords:

  • carrot;
  • high pressure;
  • freezing;
  • ice;
  • microscope

ABSTRACT

Histological changes in carrots frozen using a computer-programmed high pressure pilot unit for food processing were examined by light microscope. When raw carrots were frozen at 50 MPa, – 15°C; 100 MPa, –15°C; 150 MPa, –25°C; 200 MPa, –28°C, they were extremely damaged due to volume expansion by the formation of ice I. Conversely, carrots pressurized at 100 MPa, – 10°C (between liquid phase and ice I) and 200 MPa at –20°C (liquid phase) were not damaged because they were frozen rapidly during pressure reduction. They were not damaged even after pressurizing-then-immersing in LN2. Carrots frozen at 240 MPa, –28°C and at 280 MPa, –25°C, were also not damaged, although ice III formed. The structure of carrots frozen at 400 MPa, –20°C (ice V) was comparatively intact. When carrots were preheated at 60°C for 30 min and frozen at 100 MPa, –15°C or at 400 MPa, –20°C, damage was reduced further.