412 The nutrition handbook for food processors 00000o Fig. 19.2 Temperature maps of whey gel during ohmic heating (2, 4, and 8 min). electrodes was 305 mm. A small hole was drilled in one of the stoppers of the Plexiglas vessel to allow the release of pressure build-up during heating. Two flu- orescent fiber-optic temperature sensors were inserted through the holes into the whey gel and the solution at the same cross-sectional location that would be scanned to monitor the temperature for calibration. The absolute accuracy of the fiber-optic measurements was # 0. 2C. The use of these non-metal temperature sensors eliminated MR susceptibility artifacts c The temperature maps shown in Fig. 19.2 were obtained at 2, 4 and 8 minutes ring heating. The spatial resolution and temporal resolution were 0.94 mm and 0.64 sec respectively. PRF shift was linearly and reversibly proportional to the temperature change. The temperature uncertainties determined were about tlC for the whey gel and about t2C for the NaCl solution. The temperature maps show that there existed a gradient in the radial direction. The existence of this gradient is due to the internal heat generation of the ohmic heating process and the radiation heat transfer from particle surface through the vessel wall to the ambient. Therefore, the cold spots of the particle should be the surfaces and412 The nutrition handbook for food processors 40 40 20 100 50 0 0 60 30 70 60 60 70 50 50 40 40 30 30 20 20 20 10 10 0 70 60 50 40 30 20 10 0 70 60 50 40 30 20 10 0 0 0 60 60 80 70 50 40 40 30 20 20 10 0 2 4 8 ° ° ° Fig. 19.2 Temperature maps of whey gel during ohmic heating (2, 4, and 8 min). electrodes was 305 mm. A small hole was drilled in one of the stoppers of the Plexiglas vessel to allow the release of pressure build-up during heating. Two flu￾orescent fiber-optic temperature sensors were inserted through the holes into the whey gel and the solution at the same cross-sectional location that would be scanned to monitor the temperature for calibration. The absolute accuracy of the fiber-optic measurements was ±0.2°C. The use of these non-metal temperature sensors eliminated MR susceptibility artifacts. The temperature maps shown in Fig. 19.2 were obtained at 2, 4 and 8 minutes during heating. The spatial resolution and temporal resolution were 0.94 mm and 0.64 sec respectively. PRF shift was linearly and reversibly proportional to the temperature change. The temperature uncertainties determined were about ±1°C for the whey gel and about ±2°C for the NaCl solution. The temperature maps show that there existed a gradient in the radial direction. The existence of this gradient is due to the internal heat generation of the ohmic heating process and the radiation heat transfer from particle surface through the vessel wall to the ambient. Therefore, the cold spots of the particle should be the surfaces and corners