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Title: IMPROVING HEATING UNIFORMITY OF FRESH FRUITS IN RADIO FREQUENCY TREATMENTS FOR PEST CONTROL

Author
item BIRLA, S. - WASH. STATE UNIV.
item WANG, S. - WASH. STATE UNIV.
item TANG, J. - WASH. STATE UNIV.
item Hallman, Guy

Submitted to: Postharvest Biology and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/23/2004
Publication Date: 7/14/2004
Citation: Birla, S.L., Wang, S., Tang, J., Hallman, G.J. 2004. Improving heating uniformity of fresh fruits in radio frequency treatments for pest control. Postharvest Biology and Technology. 33:205-217.

Interpretive Summary: One of the big problems in using radiofrequency (RF) energy to heat fruits for disinfestation purposes has been heating uniformity. The variation has been such that some fruits are scalded while others are not heated sufficiently to kill insects. A fruit mover was developed to improve RF heating uniformity of larger fruits, such as oranges and apples. This fruit mover rotates and moves fruits in water subjected to RF heating. Parameters for moving and rotating fruits in the mover were selected based on consideration of vortex formation, foaming, damage to the fruits, and proportion of the volume occupied by fruits in water. RF heating uniformity of oranges and apples in the mover was assessed using infra-red imaging and direct temperature measurement with fiber-optic sensors and thermocouples. The results showed that, with rotation and movement of fruits, temperature uniformity in oranges and apples was greatly improved with less than 2.8°C and 3.1°C standard deviations, respectively, after an average temperature rise of about 30°C in 7.8 minutes.

Technical Abstract: Non-uniform heating of fresh fruits caused by variations in radio frequency (RF) fields is a major obstacle in developing postharvest insect control treatments based on RF energy. A fruit mover was developed to evaluate possibilities to improve RF heating uniformity of large fruits, such as oranges and apples, in a 12 kW batch type RF system. This fruit mover provided a means to rotate and move fruits in water when subjected to RF heating. Parameters for moving and rotating of fruits in the developed mover were selected based on consideration of vortex formation, foaming, damage to the fruits, and volume occupied by fruits in water. RF heating uniformity of oranges and apples in the mover was assessed using an infra-red imaging technique and a direct temperature measurement with fiber-optic sensors and thermocouples. The results showed that, with rotation and movement of fruits, temperature uniformity in oranges and apples was greatly improved with less than 2.8°C and 3.1°C standard deviations, respectively, after an average temperature rise of about 30°C in 7.8 min. The fruit mover can be used to develop a treatment protocol for disinfesting fresh fruits and to simulate industrial scale and continuous treatment systems.