Submitted to: Biosystems Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/23/2015
Publication Date: 7/1/2015
Citation: Li, W., Wang, K., Chen, L., Johnson, J.A., Wang, S. 2015. Performance of controlled atmosphere/heating block systems for assessing insect thermotolerance. Biosystems Engineering. 135:1-9. doi: 10.1016/j.biosystemseng.2015.01.006. Interpretive Summary: Increasing concern over the use of fumigants that may be harmful to the environment or human health make it necessary to develop alternative non-chemical treatment for postharvest disinfestation of stored products. Combining the rapid heating provided by radio frequency energy with low oxygen and high carbon dioxide environments could result in practical disinfestation treatments without adversely affecting product quality. A laboratory system for determining treatment protocols was developed, using a computer controlled heat block system to which various gases could be added. Stability of block temperatures, gas concentrations and heating rates are important system performance characteristics that may affect insect mortality. This study evaluated the effect of different gas temperatures and flow rate on system heating rates and temperature uniformity, the effect of different gas channel designs, the gas tightness of the system and stability of gas concentrations. Results showed that the laboratory system had a relatively constant leakage rate and kept variations in gas concentration to within 0.2% or less, resulting in relatively stable gas concentrations. A gas channel design that resulted in the added gas being heated to treatment temperatures before entering the treatment chamber did not affect temperature uniformity, regardless of heating rates. Temperature data from the treatment chamber showed that final temperatures and heating rates could reach targeted values even under a relatively high gas flow rate. The recorded performance of the CA-HBS suggests that it would be useful in assessing insect mortality response to high temperature controlled atmosphere treatments, as well as improving treatment efficiency and reducing treatment costs.
Technical Abstract: Heated controlled atmosphere (CA) treatments have potential as alternatives to chemical fumigation for disinfesting postharvest stored products. To determine accurately the minimal thermal requirements to kill target insects over a wide range of temperatures and CA conditions, it is desirable to develop a model system to assess quickly the target insect thermotolerance. This study evaluated the gas tightness of the new controlled atmosphere/heating block system (CA-HBS) and the stability of gas concentrations, and determined temperature variations in the treatment chamber with and without added gas and under different gas channel designs and heating rates. The results showed that the new CA-HBS had a relatively constant leakage rate and kept O2 and CO2 concentration variations to within +/-0.067% and +/-0.167% at three set points (1% O2 / 15% CO2, 2% O2 / 17% CO2, and 2% O2/ 20% CO2), resulting in relatively stable gas compositions. With the long gas channel design, temperature variations in the treatment chamber were not influenced by the addition of gas or by heating rates. The performance of the CA-HBS indicated that this model system could be used for rapid assessment of pest thermotolerance.