| A large number of rice was damaged by pest or mildew during storage every year. Although chemical fumigation methods could achieve certain effect, they could result in some environmental problems, insect resistance and so on. It could’t meet the requirements of healthy, organic food of consumers. Microwave with penetrability, could have good effects on different development stages of pests and mildew. Pulse microwave is a special microwave with speediness, efficient and environmental protection. It shows considerable potential for killing cells and preventing mildew in food with low temperature. In this paper, using rice, pests (rice weevil) mould (Aspergillus parasiticus) as raw materials, the effects of pulsed microwave on rice quality was investigated, and compared to the effect of conventional microwave treatment, to provide a suitable processing technology for insect disinfestations and mildew-proof. Here, we also studied the effect of pulsed microwave on physiological and biochemical characteristics of Aspergillus parasiticus and rice weevil to provide a theoretical basis for pulsed microwave control of mildew in rice and other food products. The results were as follows.1. The process of the prevention of rice storage pulse microwave. Using rice, rice weevil and Aspergillus parasiticus as raw materials, the effects of rice quality, rice weevil and Aspergillus parasiticus lethality were investigated. The results show that after pulsed microwave irradiation, the rice temperature increased significantly and the broken rice rate has increased (0.7%-3.4%), the overall sensory changed. The rice moisture content decreased slightly and free fatty acid content elevated. Pulse microwave can significant effect pest lethal. The optimal dose of pulsed microwave technology for the 7.5 w/g, pulse width of 300 ms, interval time of 50 ms, the total time of 30 s. At this time insect mortality was 100% and the mortality of Aspergillus parasiticus was 83.2%. The rice quality was good.2. The effect of pulse microwave on rice quality:Using rice as raw materials, to compare the difference between pulse microwave and high does ordinary microwave (H), low does ordinary microwave. Effects of rice quality after microwave treated were investigated. After pulsed microwave treated, rice temperature, crack percentage, broken rice were lower than normal microwave, but iodine blue value increased slightly. Content of volatile flavor compounds decreased, and some new generation of volatile substances were produced after microwave. The pulse microwave produced less volatile substances than ordinary microwave. The rice treated by microwave closed to the untreated samples, which extrapolates to that the rice treated by pulse microwave had a relatively small damage. The rice by pulsed microwave processing had a lower consistency coefficient and flow variable index number. During temperatures scan, pulsed microwave rice had higher pasting temperature, G’, G" than ordinary high microwave treatment group.3. Effects of pulse microwave radiation on organisms. The biological effects of rice weevil and A.parasiticus were investigated after pulsed microwave. The result shows that after pulsed microwave treatment, A.parasiticus surface morphology appear shrinkage and curling. Hyphae and spores cell membrane permeability significantly raises, intracellular environment acidification, and intracellular Ca2+ concentration rise. Under certain conditions, mycelia plasma membrane appear electroporation led to its intracellular material dissolution increases suddenly. At electroporation point conditions, high intensity pulse microwave could reduce the growth of A.parasiticus, but low intensity could extend the Logarithmic growth period and increase proliferation.Pulsed microwave treatment could reduce the activity of acetylcholinesterase, alkaline phosphatase of rice weevil, alter the behavior of rice weevil and couse nervous excitement. Whatever, Pulsed microwave treatment could reduce the hatchability of the rice weevil viability. |
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