**3. Effect of HHP on technological properties of tofu**

Tofu with 0, 2.5 or 5% trehalose was pressurized at 100–686 MPa and approximately -20 °C for 60 min to determine changes in temperature and sensory evaluation of high-pressurefrozen tofu as affected by trehalose.

Fig. 3. Cryo-scanning electron micrographs of tofu frozen at high pressure. Tofu was pressurized at 100–686 MPa and approximately −20 °C for 60 min. After decompression, it was left in the pressure medium for 30 min then thawed at 20 °C. Control: unfrozen tofu (From Fuchigami et al., 2002).

subjected to pressures of 0.1, 200, 400, and 600 MPa for 20 min. Under these conditions, lipoxygenase in citrate-phosphate buffer lost more than 80% of its activity at alkaline pH, whereas it was completely inactivated at acidic conditions and pressure treatment of 400 and 600 MPa (Tangwongchai et al., 2000). In Tris buffer, lipoxygenase activity was significantly inactivated at pH 9.0 and 400 MPa and lost all activity at 600 MPa and all pH values. Similar results were observed by Seyderhelm et al. (1996) who reported that lipoxygenase in Tris buffer pH 7.0 was completely inactivated at 600 MPa and temperatures

Tofu with 0, 2.5 or 5% trehalose was pressurized at 100–686 MPa and approximately -20 °C for 60 min to determine changes in temperature and sensory evaluation of high-pressure-

Fig. 3. Cryo-scanning electron micrographs of tofu frozen at high pressure. Tofu was pressurized at 100–686 MPa and approximately −20 °C for 60 min. After decompression, it was left in the pressure medium for 30 min then thawed at 20 °C. Control: unfrozen tofu

45 and 50 °C for 10 min and 5–10 min, respectively.

frozen tofu as affected by trehalose.

(From Fuchigami et al., 2002).

**3. Effect of HHP on technological properties of tofu** 

Tofu froze during pressurization at 100 or 686 MPa; conversely, tofu did not freeze between 200 and 600 MPa and -20 °C, but it froze rapidly when the pressure was released. It was found that tofu frozen at 0.1, 100 or 686 MPa had larger ice crystals and was firmer (less like unfrozen tofu) than tofu frozen at 200–600 MPa. In the sensory evaluation, results showed that mouth feel (texture. of tofu frozen at 400 MPa) was more like the control when 2.5% trehalose was added (Fuchigami et al., 2002).

The micro structure of the tofu gel network high pressure frozen at 686 MPa was compared with untreated tofu (Fig. 3). Tofu (0% trehalose) frozen at 0.1–500 MPa maintained a comparatively coarse network (data not shown), but tofu gel frozen at 686 MPa was compressed. Compression of the protein gel network might have occurred above 600–686 MPa; however, the gel network in tofu frozen at 686 MPa became coarse with the addition of trehalose. This indicates that trehalose with high-pressure-freezing appears to protect against compression (effects of concentration of protein and coagulants on frozen tofu) (Fuchigami et al., 2002).
