Optimization of Radio-Frequency Heating Conditions to Achieve Uniform Pasteurization of Irregularly Shaped Spices: The Case of Star Anise

Radio-frequency (RF) heating has been proven effective in inactivating foodborne pathogens or fungi in spices. However, non-uniformity heating remains a major obstacle limiting RF treatment application in the commercial pasteurization of irregularly shaped spices. This study evaluated the effects of star anise arrangement, packaging materials, and dual-bag placement on RF heating uniformity after identifying the optimal input power and electrode gap. The optimal conditions were 400 W and an electrode gap of 5 cm. Under these conditions, heating uniformity was significantly improved by a staggered arrangement, using bags with 0.16 mm aluminum foil (plastic/foil composite) and face-to-face placement of two bags; the average heating uniformity index of the stacked packages decreased from 0.30 to 0.135, corresponding to a reduction of approximately 55.0%. These findings provide practical guidance for scalable, eco-friendly RF pasteurization of irregular spice products, emphasizing key considerations in sample arrangement and packaging/bag placement to control heating uniformity.