Effective Inactivation And Degradation Of Aspergillus Flavus And Aflatoxins In Rough Rice Using Pulsed Light, Ultraviolet And Infrared Radiation

Fungi and their mycotoxins produced in grains are the main factors that cause the reduction of output and affection of human health. Rice as the most important food in China is facing the most serious problem on pollution of Aspergillus flavus and aflatoxins. Therefore, new methods of simultaneous decontamination and detoxication were developed. The mechanisms of inactivation of pulsed light (PL) and ultraviolet radiation technology were studied. The reaction kinetics characteristics of PL and ultraviolet radiation were investigated. The PL sterilization process was optimized. Infrared radiation disinfection process on freshly harvest rice and stored rice were studied. PL degradation effects of aflatoxin and degradation kinetics in different medium and biological toxicity and genetic toxicity of degradation products were determined.The study of the inactivation mechanism of PL and ultraviolet radiation on Aspergillus flavus spores showed that, PL radiation destroied spore cell wall structure and led to cell wall perforation and shrinkage by producing the high-energy photochemical and photothermal effects, which caused the the leakage of cytoplasm and cell death. Ultraviolet radiation has non-visible damage on the cell wall. The spore collapse was due to the ultraviolet radiation directly effect on the material intracellular.By setting the radiation fluence as a variable, the sterilization effect of pulsed light and ultraviolet radiation were studied. The inactivation curves well fitted the Weibull+Tail model and Weibull model. After comparing the unit energy consumption and inactivation rate, the obtained results showed that, ultraviolet has higher unit energy consumption and PL has higher inactivation rate. It needed7min for ultraviolet to inactive105cfu/g spores and for the same inactivation populations, PL only need30s.The combined PL and holding processing can greatly improve the inactivation effect and simutanious drying of rice. The reduction could achieved5.2log cfu/g, the drying rate could reached up to4.4%per minute. After drying, moisture can be reduced by4.1percentage points. And after checking the quality indexes, no negative effects were showed on rice milling quality.The freshly harvest rice with different initial moisture content (IMC) could be treated by infrared radiation heating to60℃and holding at same temperature for different time to achieve sterilization and drying effect. For the rice with IMC higher than21.1%, the optimal conditions was infrared radiation to60℃, holding for120min, Aspergillus flavus spores could reduce8.3log cfu/g. The MC plays a vital role in sterilization, the higher MC lead to higher sterilization effect. Therefore, wetting the surface of dried rice and followed by infrared heating, could significantly improve the disinfection effect. The optimal conditions for sterilization of stored rice was wetting husk to obtain the whole MC of19.4%and treated by infrared radiation at60℃and followed by20min of holding and natural cooling. Aspergillus flavus spores can be reduced by7.4log cfu/g and final moisture content of13.8%. The rice can be safe storage directly.PL has strong degradation effect on aflatoxin B1(AFB1) and aflatoxin B2(AFB2). HPLC analysis showed, after exposed for10s of PL, at fluence of28.52J/cm2, the aflatoxin B1and B2at high concentration (500ppb) could be reduced by96.6%and91.7%respectively. The degradation dynamics was well fitted the second order kinetic model. The biological toxicity and genotoxicity of the degradation products were measured by using Artemia nauplii and Ames test methods. The results showed the toxicities were completely eliminate after the PL treatment.PL has good degradation effects on different medium. For rough rice treated at the fluence of84.35J/cm2, AFB1and AFB2were decreased by75.0%and39.2%, respectively. For rice bran treated at the fluence of16.1J/cm, AFB1and AFB2were decreased by90.3%and86.7%, respectively. The PL degradation kinetics fitted the second order reaction. The degradation rate has positive relationship with the initial aflatoxin concentration and radiation intensity.Research showed that, ultraviolet, pulsed light and infrared radiation could greatly inactive on rice Aspergillus flavus. PL could reduce of aflatoxin toxin as well. Ultraviolet, infrared radiation technology and especially the high energy PL radiation technology are a group of light technologies which can be applied to improve the food safety, environmental friendly, energy efficiency technologies on rice.