High Pressure Bioscience. Texture and Structure of High-Pressure-Frozen Foods.

To determine the effect of high-pressure-freezing on quality, carrots and tofu (soybean curd) were frozen at 100 MPa (ice I), 200 MPa (liquid phase), 340 MPa (ice III), 400, 500, 600 MPa (ice V) or 700 MPa (ice VI) at ca. -20 °C then thawed at atmospheric pressure. The texture and structure of these foods frozen at 200 ∼ 400 MPa improved in comparison to foods frozen at 0. 1 MPa (frozen in freezers at -20 °C, -30 °C or -80 °C) or 100, 600 and 700 MPa. However, ice crystals were observed even in tofu frozen at 200 MPa ∼ 400 MPa. Therefore, tofu was also thawed at a high pressure and then the pressure was reduced. Texture and structure (pore size) of tofu frozen at 200∼400 MPa were the same as for unfrozen tofu. This indicated that phase transitions (ice VI → ice V → ice III → liquid → ice I) occurred during reduction of pressure at 20°C, during freezer storage or while thawing at 0. 1 MPa Thus, high-pressure freezing-thawing at 200∼400 MPa was effective in improving the quality of frozen foods.