Radio frequency tempering of frozen pacific sauries (Cololabis saira) under batch and continuous mode: Temperature distribution and energy consumption evaluation

To investigate the influences of modes and operating parameters on the radio frequency (RF) tempering uniformity of a pack of frozen pacific sauries, a 27.12 MHz RF equipment was employed for sauries tempering with different input power and electrode gaps under batch and continuous mode. Nine frozen sauries were placed in the RF chamber and tempered under different input power (200, 400, 800, 1,600 W), electrode gaps (7, 8, 9 cm) under batch and continuous tempering mode. With a target end‐point tempering temperature of −4°C. Results showed 200 W/9 cm resulted in the longest tempering time (16.44, 15.43 min) and 1,600 W/7 cm was the shortest (2.95, 3.54 min) under batch mode tempering, respectively. The processing conditions of 200 W/9 cm and 200 W/7 cm under batch mode, and 200 W/8 cm, 200 W/9 cm, 400 W/9 cm, 800 W/8 cm under continuous mode all produced a final sample surface temperature distribution within the range of −10°C to 20°C, which indicated a reasonable tempering process. The area of the high temperature zone (10°C < T ≤ 20°C) of tempered sauries under 200 W/9 cm decreased from 0.28% to 0.23% when switching from batch to continuous mode. This implies that continuous RF tempering could reduce overheating and improve tempering uniformity of sauries. PRACTICAL APPLICATIONS: Tempering rate, temperature distribution, and energy consumption are the most important concerns to researchers and the industry since tempering temperature and time are highly correlated to fish product quality. Results in this study showed both batch and continuous mode RF tempering could achieve reasonable tempering effect to a pack of frozen sauries. The application of continuous tempering system is more desirable than the batch ones, which can be applied to the tempering industry with higher throughput and connect to the following continuous processing unit operations. This study will broaden the knowledge of food engineers and provide an alternative technology of aquatic product tempering, and the parameters used in this study can assist technologists for the development of commercial equipment.