STUDIES ON HIGH-PRESSURE-FREEZING OF VEGETABLES

采用计算机编程高压试验装置(a) （phi25*H80mm, Max.400MPa, -30 C）和Dr.Chef (B) (phi60*H200mm, 700MPa, -20 C)，研究了高压冷冻对胡萝卜和大白菜质地、果胶成分和组织结构的影响。(A)生胡萝卜在50MPa， -15℃冷冻时；100MPa, -15℃；150MPa, -25℃；而在100MPa、-10 C（液相与冰的边界）和200MPa C（液相）下，由于胡萝卜在减压过程中迅速冻结，即使先加压再浸泡在LN_2中也没有损坏，因此胡萝卜在减压过程中没有受到损坏。在280MPa， -25 C下冷冻的胡萝卜也没有损伤，但在240MPa， -28 C下冷冻的胡萝卜有轻微损伤，但形成了冰III。在400MPa下冷冻的胡萝卜结构较好，但比在200MPa下加压的胡萝卜结构差。(B)生胡萝卜或焯过3分钟的胡萝卜在-18 -20 C下加压45分钟，然后在20 C下解冻。当胡萝卜在100MPa（冰I）下冷冻时，硬度下降，应变增加。在200MPa（液体）、340MPa（冰III）、400MPa（冰V）下冷冻的胡萝卜质地较好。当压力大于500MPa时，应变增大。200mpa、340 mpa和400MPa冷冻胡萝卜的果胶释放量和组织损伤均小于100 mpa和700MPa（冰VI）冷冻胡萝卜。在200和340MPa下冷冻后，将胡萝卜储存在-30ºC的冰箱中。其硬度降低，应变增大，但织构和组织结构优于在-30℃（0.1MPa）下冷冻后保存。研究发现，200,340和400MPa的高压冷冻能有效改善冷冻胡萝卜和大白菜的质地和组织结构。

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.