Developing a spouted bed for combined radio frequency-hot air treatments to improve the heating uniformity in high-moisture carrot cubes

Abstract

Uneven and thermal runaway heating is the biggest obstacle to industrial applications of radio frequency (RF) technology, while the existing research mainly focuses on the RF heating uniformity of low-moisture foods with fewer reports about the useful solutions to avoid heterogeneous heating of high-moisture foods. Thus, the combined RF-hot air treatment in a newly designed spouted bed (RFHASB) was developed in this study to improve the RF heating uniformity of fresh carrot cubes selected as the high-moisture model sample. This RFHASB was used to evaluate effects of four processing parameters (cone angle, nozzle diameter, inlet air speed and electrode gap) on the RF heating rate and uniformity of carrot cubes with comparison of those between the RFHASB and the hot air treatment alone in the spouted bed (HASB). The results showed that the RFHASB effectively alleviated the non-uniform heating in the treated high-moisture carrot cubes through mixing and stirring particles. Both heating rate and uniformity index in RFHASB increased with decreasing cone angles and electrode gaps but decreased when nozzle diameters and inlet air speeds were reduced. The RFHASB had better heating performances than the HASB. These findings may provide the theoretical basis for the effective drying of high-moisture fresh fruits and vegetables in RFHASB.