STUDIES ON HIGH-PRESSURE-FREEZING OF VEGETABLES

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Effect of high-pressure-freezing on texture, pectic composition and histological structure of carrots and Chinese cabbages was investigated using a computer-programd high pressure pilot unit (A) (phi25*H80mm, Max.400MPa, -30ﾟC) and Dr.Chef (B) (phi60*H200mm, 700MPa, -20ﾟC).(A) When raw carrots were frozen at 50MPa, -15ﾟC ; 100MPa, -15ﾟC ; 150MPa, -25ﾟC ; 200MPa, -28ﾟC,they were extremely damaged due to volume expansion by the fromation of ice I.Conversely, carrots pressurized at 100MPa, -10ﾟC (border between liquid phase and ice I) and 200MPa at -20ﾟC (liquid phase) were not damaged, because they were frozen rapidly during reduced pressure, and not damaged even after pressurizing-then-immersing in LN_2. Carrots frozen at 280MPa, -25ﾟC,were also not damaged either, but those at 240MPa, -28ﾟC were injured slightly, although ice III formed. The structure of carrots frozen at 400MPa was comparatively good but worse than those pressurized at 200MPa.(B) Raw or 3 min blanched carrots were pressurized for 45 min at -18ﾟC--20ﾟC and then thawed at 20ﾟC.When carrots were frozen at 100MPa (ice I), firmness decreased and strain increased. Texture of carrots frozen at 200MPa (liquid), 340MPa (ice III), 400MPa (ice V) was good. When pressure rose above 500MPa, the strain increased. Release of pectin and histological damage in carrots frozen at 200,340 and 400MPa were less than carrots frozen at 100 and 700MPa (ice VI). After freezing at 200 and 340MPa, carrots were stored in a freezer (-30ﾟC). Their firmness decreased and strain increased, but their texture and histological structure were better than those frozen at -30ﾟC (0.1MPa) and stored.High-pressure-freezing at 200,340 and 400MPa was found to be effective in improving both the texture and histological structure of frozen carrots and Chinese cabbages.