Effective Disinfection of Rough Rice Using Infrared Radiation Heating

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 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 60°C 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.

Effectiveness of pulsed light treatment for degradation and detoxification of aflatoxin B1 and B2 in rough rice and rice bran

“…A. flavus was grown in potato dextrose agar (PDA) (Sigma, St. Louis, MO, USA) at 28 C for 7 days (Kim, Campbell, Mahoney, Chan, & Molyneux, 2004). A conidial suspension of 10 5 cfu/mL was prepared by flooding the culture plates with 0.03% Tween 80 (w/w) (Wang et al, 2014). A volume of 10 ml of the spore suspension was pipetted onto 500 g rough rice in a conical flask, sealed by a double layer aluminum foil, and kept in a 28 C incubator for 14 days until the mold growth was observed.…”

Radiant heat treatments for corn drying and decontamination

“…Wang et al () demonstrated that the energy flux associated with IR heating could result in microbial decontamination in rice with shorter heating duration compared to convective heated air. The authors reported the potential to inactivate A .…”

“…flavus molds on rice by using a catalytic IR emitter powered by natural gas. The results by Wang et al () for rice decontamination were based on batch treatments and may not translated to corn drying applications. Compared to rice, corn is less susceptible to stress‐crack formation, and may endure larger doses of IR energy before sensory qualities are compromised.…”

Simultaneous decontamination and drying of rough rice using combined pulsed light and holding treatment

“…The samples were incubated for 0, 10, 20, 40, 60, 120 and 240 min. The temperature of 60 °C was chosen based on our previous findings, which confirmed that high drying rate, milling quality and effective disinfections and disinfestation could be achieved at a holding temperature of 60 °C …”

“…Much work has been done in our previous research using electromagnetic radiation for rough rice drying. Our reported results demonstrated that rapidly heating rough rice to 60 °C followed by a tempering/holding treatment for several hours can be used as an effective approach to achieve high drying rate and good milling quality . Heretofore, to our best knowledge there are no reports in the literature on decontamination and drying of rough rice using integrated PL and holding treatment.…”