|WANG, BEI - Jiangsu University|
|KHIR, RAGAB - University Of California|
|EL-MASHAD, HAMED - University Of California|
|ATUNGULU, GRIFFITHS - University Of Arkansas|
|MA, HAILE - Jiangsu University|
|QU, WENUAN - Jiangsu University|
|WU, BENGANG - Jiangsu University|
Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/11/2014
Publication Date: 8/11/2014
Citation: Wang, B., Khir, R., Pan, Z., El-Mashad, H., Atungulu, G.G., Ma, H., McHugh, T.H., Qu, W., Wu, B. 2014. Effective disinfection of rough rice using infrared radiation heating. Journal of Food Protection. 77(9):1538-1548.
Interpretive Summary: Aspergillus flavus is a common and typical pathogen that grows on rough rice under insufficient drying and inappropriate storage conditions. It produces aflatoxins that can cause acute and chronic toxicity in human. The objective of this study was to investigate the effect of infrared (IR) heating and tempering treatments on disinfection of Aspergillus flavus in freshly harvested rough rice and storage rice. Both fresh and rewetted storage rice were inoculated with Aspergillus flavus spore and treated with infrared heating, followed by tempering at various time lengths. The tempering time needed to achieve a 5-log reduction of A. flavus in rice of different initial moisture contents was estimated by the log-linear plus tail model. The recommended conditions of simultaneous disinfection and drying for fresh rice was IR heating to 60ºC followed by tempering for 120 min and natural cooling. For the rewetted dry rice with an initial moisture content of 19.4%, the recommended condition for disinfection and drying required only 20 min of tempering, revealing that high relative humidity of the tempering environment had a positive effect on the disinfection of A. flavus spores.
Technical Abstract: The objective of this study was to investigate the effect of infrared (IR) heating and tempering treatments on disinfection of Aspergillus flavus in freshly harvested rough rice and storage rice. Rice samples with initial moisture contents (IMCs) of 14.1 to 27.0% (wet basis) were infected with A. flavus spores before the tests. The infected samples were heated by IR radiation to 60°C in less than 1 min, and then samples were tempered at 60°C for 5, 10, 20, 30, 60, or 120 min. High heating rates and corresponding high levels of moisture removal were achieved using IR heating. The highest total moisture removal was 5.3% for the fresh rice with an IMC of 27.0% after IR heating and then 120 min of tempering. IR heating followed by tempering for 120 min resulted in 2.5- and 8.3-log reductions of A. flavus spores in rough rice with the lowest and highest IMCs, respectively. To study the effect on disinfection of rewetting dried storage rice, the surface of the dry rice was rewetted to achieve IMCs of 14.7 to 19.4% (wet basis). The rewetting process for the dry rice had a significant effect on the effectiveness of disinfection. IR heating followed by tempering for 60 min resulted in 7.2-log reductions in A. flavus on rewetted rough rice. The log-linear plus tail model was applied to estimate the tempering time needed to achieve a 5-log reduction of A. flavus in rice of different IMCs. At least 30 and 20 min of tempering were needed for fresh rice and rewetted rice, respectively, with the highest IMCs. The recommended conditions of simultaneous disinfection and drying for fresh rice was IR heating to 60ºC followed by tempering for 120 min and natural cooling, resulting in a final MC of 16.5 to 22.0%, depending on the IMC. For the rewetted dry rice with an IMC of 19.4%, the recommended condition for disinfection and drying involved only 20 min of tempering. The final MC of the sample was 13.8%, which is a safe MC for storage rice.