Improvement of radio frequency (RF) heating uniformity on low moisture foods with Polyetherimide (PEI) blocks

Radio frequency (RF) heating is rapid, volumetric, and can penetrate most food packaging material. Thus, it is suited for in-packaged food pasteurization applications. However, the non-uniform heating problem needs to be resolved. In this study, a method of adding Polyetherimide (PEI) cylindrical blocks on top of and at the bottom of peanut butter samples in a cylindrical jar (d=10cm, h=5cm) was evaluated to improve RF heating uniformity. A computer simulation model built with COMSOL Multiphysics® was used for heating pattern prediction, and a new temperature uniformity index was proposed to suitably evaluate pasteurization process heating uniformity. Results showed that a pair of PEI blocks with a diameter of 8cm among all five diameters (2, 4, 6, 8, and 10cm) added to the cold spots of a given peanut butter sample could make the sample reach the best heating uniformity. Furthermore, the best height of PEI blocks with a diameter of 8cm that allows the sample to be heated most uniformly was found to be 1.3cm after sweeping from 0.1 to 2.3cm with a step of 0.1cm. Simulation results also showed that the combination of PEI surrounding and the addition of 8cm diameter PEI blocks could further control the temperature distribution range in peanut butter within 7.1°C when the peanut butter was heated from 23 to 70°C. The newly developed temperature uniformity index provided a more reasonable evaluation on heating uniformity of pasteurization process than the traditional uniformity index.