ARS | Publication request: Evaluating the storage environment in hypobaric chambers used for disinfesting fresh fruits

Submitted to: Biosystems Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 8, 2011
Publication Date: January 11, 2012
Repository URL: http://handle.nal.usda.gov/10113/55012
Citation: Jiao, S., Johnson, J.A., Fellman, J.K., Mattinson, D.S., Tang, J., Davenport, T., Wang, S. 2012. Evaluating the storage environment in hypobaric chambers used for disinfesting fresh fruits. Biosystems Engineering. 111(3):271-279.

Interpretive Summary: Export of fresh fruits such as apples or cherries to Japan requires quarantine treatments targeting codling moth. Normally these treatments use the environmentally damaging fumigant methyl bromide. Low pressure (LP) treatments, applied in hypobaric chambers at low temperatures, have the potential to replace fumigants for postharvest disinfestation of fresh fruits. Most LP systems targeting fresh fruits and vegetables utilize a method to maintain high humidities, thus water loss, commodity respiration, and production of the ripening hormone ethylene are reduced under LP conditions to prevent wilting and fruit ripening during storage. Critical to the success of these treatments is maintaining the stability of pressure, temperature and relative humidity within the chambers. A validated computer simulation model was used to determine the thickness of insulation foam needed to cover the hypobaric chamber walls in order to stabilize the air temperature within the chambers. The stability of pressure, temperature and relative humidity levels in the LP system was evaluated together with various O2 concentrations, evacuation, venting and leakage rates. Results showed that the added foam covering the chambers maintained the temperature variation of the hypobaric chamber wall to within ±0.2°C and inside air to within ±0.1°C. The regulating system kept pressure to within ±1% of the set point, and maintained relative humidity at nearly saturated levels (>98%) under various air exchange rates and pressures, with a chamber leakage rate of 0.07 mm Hg/h and LP system leakage rate of 3.6 mm Hg/h. Since the hypobaric chamber displayed adequate performance characteristics, further studies will be conducted to evaluate LP treatment efficacy for fresh fruits.

Technical Abstract: Low pressure (LP) treatment has potential as an alternative non-chemical postharvest disinfestation method for fresh fruits. A validated computer simulation model was used to determine the thickness of insulation foam needed to cover the hypobaric chamber walls in order to stabilize the air temperature within the hypobaric chambers that were housed in a cold storage room with fluctuating air temperatures. The stability of pressure, temperature and relative humidity levels in the LP system was evaluated together with various O2 concentrations, evacuation, venting and leakage rates. Results showed that the added foam covering the chambers maintained the temperature variation of the hypobaric chamber wall to within ±0.2°C and inside air to within ±0.1°C. The regulating system kept pressure to within ±1% of the set point, and maintained relative humidity at nearly saturated levels (>98%) under various air exchange rates and pressures, with a chamber leakage rate of 0.07 mm Hg/h and LP system leakage rate of 3.6 mm Hg/h. Given that the hypobaric chamber displayed adequate performance characteristics, further studies will be conducted to evaluate LP treatment efficacy for fresh fruits.