TEXTURE AND STRUCTURE OF HIGH-PRESSURE-FROZEN FOOD GELS.

为了确定高压冷冻对产品质量的影响，将蛋白质凝胶（豆腐凝胶、蛋奶冻凝胶、明胶凝胶）和多糖凝胶（琼脂、魔芋胶、卡拉胶-槐豆胶、凝乳胶和结冷胶）分别在100 MPa（冰I）、200 MPa（液相）、340 MPa（冰III）、400、500、600 MPa（冰V）或700 MPa（冰VI）下冷冻，温度为-20℃。将凝胶还原至常压后，在-30ºC的温度下保存，然后在20ºC的温度下解冻。然后与常压（0.1 MPa）下冷冻凝胶（-20、-30或-80）的织构和结构（冷冻扫描电镜观察）进行比较。在0.1、100、600和700 MPa冷冻条件下，无糖凝胶的质地和结构与原始凝胶有显著差异。另一方面，当所有凝胶（魔芋除外）在200 ~ 400 MPa下冷冻时，冷冻凝胶的质量比在0.1和100 MPa（冰I）下冷冻的凝胶更好。然而，其质量与未冷冻的凝胶不同。随着蔗糖添加量的增加，所有凝胶的外观、质地和结构都有所改善。为了确定减压过程中冰的相变，在相同的高压下解冻高压冷冻凝胶。后来，压力降低了。在200 ~ 500 MPa下冷冻后，凝胶的结构与原始凝胶相同。这表明相变（从冰VI到冰v到冰III到液体到冰I）发生在降低压力（-20 C）或在冷冻库中储存期间。在200-400 MPa和-20℃的高压下，凝胶不冻结（过冷），而在减压后，凝胶快速冻结。由此可见，200-400 MPa的高压冷冻能有效提高冷冻凝胶的质量。

To determine the effect of high-pressure-freezing on quality, gels composed of protein (tofu, egg custard and gelatin gel) and gels of polysaccharides (agar, konjac, carrageenan-locust bean gum, curdlan and gellan gums) were frozen at 100 MPa (ice I), 200 MPa (liquid phase), 340 MPa (ice III), 400, 500, 600 MPa (ice V) or 700 MIPa (ice VI) at ca. -20ﾟC.After reducing to atmospheric pressure, gels were stored at -30ﾟC then thawed at 20ﾟC.Texture and structure (cryo-SEM observation) were then compared with gels frozen (-20ﾟC, -30ﾟC or -80ﾟC) at atmospheric pressure (0.1 MPa). In gels without sucrose, frozen at 0.1, 100, 600 and 700 MPa, texture and structure differed significantly from original gels. On the other hand, when all gels (except konjac) were frozen at 200 - 400 MPa, the quality of frozen gels improved compared to gels frozen at 0.1 and 100 MPa (ice I). However, quality differed from unfrozen gels. With the increase of sucrose, appearance, texture and structure of all gels improved. To determine phase transition of ices during depressurization, high-pressure-frozen gels were thawed at the same high pressure. Aferwards, pressure was reduced. Texture of gels frozen at 200 - 500 MPa was the same as original gels. This suggested that phase transitions (from ice VI to iceV to ice III to liquid to ice I) occurred during reduction of pressure (-20ﾟC), or during storage in a freezer. However, when gels were pressurized at 200-400 MPa and -20ﾟC, the gels did not freeze (supercooling), while after depressurization, the gels froze quickly. Thus, high-pressure-freezing at 200-400 MPa was effective in improving the quality of all frozen gels.