BEHAVIOR OF WATER AND ICE IN FOOD UNDER HIGH- PRESSURE

为了确定高压冷冻对冷冻凝胶质量的影响，在-18℃~ -20℃下，对由蛋白质组成的凝胶（豆腐凝胶和蛋奶冻凝胶）和由多糖组成的凝胶（琼脂胶、魔芋胶、卡拉胶-槐豆胶、凝乳胶和结冷胶）进行100 ~ 686 MPa的加压。还原至常压后，-30℃保存，20℃解冻。然后与在大气压（0.1 MPa）下（-20℃、-30℃和-80℃）冷冻的凝胶进行织构和结构（低温扫描电镜观察）比较。在0.1、100、600和686 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，除魔芋外，所有凝胶在200 ~ 400 MPa冷冻时，冷冻凝胶的质量都有所提高。随着蔗糖含量的增加，所有凝胶的外观、质地和结构都有所改善。为了确定加压过程中冰的相变，测定了温度。在200 ~ 400 MPa和-20℃的压力下，凝胶不冻结（过冷），但在减压后，凝胶快速冻结。冻融耐受性随凝胶种类的不同而不同。它们被分为三种类型：在冷冻过程中变硬的凝胶（豆腐、魔芋），变软的凝胶（琼脂、卡胶-卡拉胶、未取代结冷胶凝胶）和不改变的凝胶（凝乳、取代形式-结冷胶、ioa -卡拉胶凝胶）。结果表明，在200 ~ 400 MPa的温度下进行移压冷冻可以有效地提高冷冻凝胶的质量。

To determine the effect of high-pressure-freezing on the quality of frozen gels, gels composed of protein (tofu and egg custard gel) and gels of polysaccharides (agar, konjac, carrageenan-locust bean gum, curdlan and gellan gums) were pressurized at 100 〜686 MPa at ca. -18℃ 〜 -20℃. After reducing to atmospheric pressure, gels were stored at -30℃ then thawed at 20℃. Texture and structure (cryo-SEM observation) were then compared with gels frozen (-20℃, -30℃ or -80℃) at atmospheric pressure (0.1 MPa). In gels without sucrose, frozen at 0.1, 100, 600 and 686 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. With an increase of sucrose, the appearance, texture and structure of all gels improved. To determine the phase transition of ices during pressurization, temperatures were determined. When gels were pressurized at 200 〜 400 MPa and -20℃, the gels did not freeze (supercooled), but after depressurization, the gels froze quickly. The freeze-thaw tolerance differed with the kinds of gels being examined. They were classified in three types : gels which became hard during freezing (tofu, konjac), the gels which became soft (agar, kappa-carrageenan, unsubstituted form-gellan gum gels), and the gels which did not change (curdlan, substituted form-gellan gum, iota-carrageenan gels). Finally, pressure-shift-freezing at 200 〜 400 MPa was found to be effective in improving the quality of all frozen gels.