Experimental comparison of microwave and radio frequency tempering of frozen block of shrimp

In this study, microwave and radio frequency tempering of frozen shrimp were compared experimentally in terms of tempering rate and uniformity. To do this, a block of frozen shrimp (1.75 kg) was tempered from an initial temperature of -22 degrees C to between -5 and -3 degrees C both in a microwave system (915 MHz) and a radio frequency oven (27.12 MHz). Temperatures at four different internal locations were recorded during tempering experiments by using a signal conditioner and fiber optic probes. Surface temperature was also measured using an infrared camera immediately after tempering. Time needed for temperature increase from the initial to between - 5 and - 3 degrees C at all four locations where the fiber optics were inserted was about 10 and 4 min for power settings of 500 W and 1 kW respectively when microwave tempering was performed. In case of radio frequency tempering, it took 11 and 7 min to reach between - 5 and - 3 degrees C at all four locations for electrode gaps of 160 and 150 mm, respectively. Among all treatments, microwave tempering at 500 W yielded the most uniform internal temperature distribution. However, local surface overheating was observed during microwave tempering at both power settings. Radio frequency tempering, in contrast, was found to result in a uniform overall temperature distribution with no local overheating at the surface.