Studies On Microwave Sterilization Process And Mechanism Of Molds In Rice

Raw rice is one of the major food crops in China, the planting areas of rawrice are about a quarter of the total areas of food crops, the annual output of rawrice are about2/5of the total output of food crops. Raw rice being cleaned,peeled, rolled are equal to127million tons of rice. Rice is vulnerable to infectby environment of fungal during its storing, we lose about1tons rice becauseof molds in our country every year. In today’s world under the serious situationof soaring food prices, reduced inventory, rice safety and storaged problembeing one of the urgent need to solve. Microwave sterilization is one of theemerging sterilization methods in recent years, it was been widely used in foodindustry, because of its fast, efficient, safe, environmental protection and so on.This article first isolated and identified molds from moldy rice, then studied onthe microwave sterilization process and the kinetic models in the process offitting, and from the cell membrane permeability, enzyme activity, cell surfacemorphology being changed of the mechanism of microwave kill mould werestudied.1. Being isolatied and identified predominate molds in rice storing wereAspergillus, Penicillium, Rhizopus, Trichoderma, thirteen strains of molds wereidentified as follows: A flavus, A nidulans, A versicolor, A niger, A oryzae, Austus, A fumigates, P citreo-viride, P islandicu, P purpurogenum, P tardum, Roryzae, T koningii.2. To explore the process on microwave sterilization A flavus from rice.The log-periodic reduction of spores of A flavus was as indicator, effect ofmicrowave power, microwave time, and loads of rice on log-periodic reductionof spores of A flavus were investigated. Based on the single-factor experiments,microwave sterilization process was researched by response surfacemethodology and corresponding regression equation was established. Resultsshowed that optimum sterilization conditions were as follows: microwavepower of231W, microwave time of32s, and loads of rice of34g.3. To explore the killing effect of microwave treatment on molds from rice, response surface methodology was used to optimize process of microwavesterilization A niger from rice. Effects of microwave power, microwave time,and mould suspension volume on log-periodic reduction of spores of A nigerfrom rice were investigated, and corresponding regression equation wasestablished. Results showed that optimum sterilization conditions were asfollows: microwave power of231W, microwave time of4min, and mouldsuspension volume of97mL. Compared with water-bath heating treatment,effect of microwave sterilization was8.5times as much.4. In order to explore microbial kinetic during microwave treatment. Aflavus, A nidulans, P citreo-viride, P islandicum were as the research objects,under these conditions: microwave power of231W、microwave time of4minand mould suspension volume of97mL,SWeibull、Slogistic and Dose-responsefitting models were used to fit the inactivation kinetic of microwave treatmentprogress. Accuracy factor, bias factor, root mean square error and regressioncoefficients were used to compare the goodness-of-fit of fitting models. Resultsshowed that Dose-response model consistently produced better fits toinactivation kinetic of A flavus, A nidulans, P citreo-viride than others, andSWeibull model had better fits to describe inactivation kinetic of P islandicumby microwave treatment than others.5. To explore microwave sterilization mechanism, A flavus, A nidulans, Pcitreo-viride, P islandicum were selected as the research objects, no-treatmentand water-bath heating were as control experiments, including growth amount,permeability of protein, DNA and conductance rate, dehydrogenase activity, ioncontents of molds cells, morphologies of spores and hyphaes were measured.Results showed that microwave sterilization mechanism exists non-thermaleffect.