Research On Process And Kinetic Model Of Mold In Corn By Microwave Treatment

Corn is one of the major food crops in China. The output of corn is morethan rice and it becomes the highest yield of the crops from2012. Most wereinfected by mold before obtaining. During storage period, it is easier to get warmand mildewy than others and millions of corns are damaged because of itsnutrient-rich, uneven maturity and high water content. The quality is damaged andit losses the edible value. It has important economic and the social significance tothe safe storage of corn. Because of the security, effectiveness and easy to controlof microwave sterilization, it has been widely used in a variety of foodssterilization. To extend the storage time and to reduce the quality loss of corn, thetechnological conditions of microwave killing mold was studied; the inactivationmodel of mold in corn by microwave treatment was fitting; the growth of moldwas studied after microwave treatment and growth model was established; inaddition, the mechanism of microwave killing mold was studied.1.60single colonies were isolated from corn, the highest detection rate wasAspergillus, the second was Penicillium. Identified four kinds of molds in corn:Aspergillus funigatus, Aspergillus niger, Penicillium chrysogenum andPenicillium citrinum.2. To determine the microwave dose and microwave power for sterilization.Response surface method was utilized to build optimized method to kill corn A.funigatus, the corresponding regression model was established. The best conditionthat microwave kill A. funigatus was: microwave power539W, microwave dose2.5W/g. Influence factors of significance as follows: microwave power,microwave dose. Through three validation experiments, A. funigatus sporesreduced logarithmic cycles was1.0496±0.005, and the fatality rate was (91.08±1.23)%, which accord with the theoretical value. Examine the inactivation effectof other molds: A. niger, P. chrysogenum and P. citrinum, the fatality rate were95.00%、95.29%and95.38%, the values all over90%.3. Four kinds of molds were fitted by the method of inactivation model of microwave treatment. The value of R2in Weibull model respectively were0.9971、0.9903、0.9927and0.9875for A. niger, P. chrysogenum and P. citrinumand in linear model were0.970.、0.9192、0.9459and0.9393. The value of R2inWeibull model was all higher than in linear model. The result shows: Weibullmodel was better than the linear model to fit the inactivation model of moldspores by microwave treatment.4. To further clarify the effect of microwave treatment to corn mold, threefactors three levels of response surface method was applied to processoptimization of killing A. niger by microwave irradiation. The best condition ofsterilization was microwave power119w, microwave time6min, the loadingcapacity50g. By three validation experiments, A. niger spore reduce logarithmiccycles was1.3769±0.107, the crack ratio was0. Tested and predicted valueswere simila basically. Moisture content of corn was reduced to (23.97±1.21)%from (28.11±0.68)%.5. Application of water bath and microwave to treat four kinds of moldspores, by measuring the growth and fitting the growth curve model to predict theeffect of two kinds of treatment. The results show: the water bath heating andmicrowave treatment all can kill the mold spores, but the mold spores were notcompletely dead. The living molds still follow the Logistic growth model. Theyhave demurrage, logarithmic phase and stable phase. But the growth momentumwas insufficient, lag phase increased and population intake capacity declined. Theresults also show: lag phase of molds by microwave effect was longer than bywater bath and population intake capacity was lower than the water bath.6. By detecting absorbance value of the protein and DNA and electrolyteleakage of the four kinds of spores, which were treated by microwave and waterbath. In the same condition, the values of the protein and DNA and electrolyteleakage of the four kinds of spores by microwave treatment were higher than bywater bath.The result shows that the damage degree to the cell membrane bymicrowave treatment was greater than by the water bath. And the non-thermaleffect exists in the process of microwave sterilization7. Before and after microwave treatment, observing the morphology of A.niger spore by atomic force microscope. The result shows that: there were manydifferences between mold spore morphology before and after the microwavetreatment. The form of spores was full and the suface was relatively smoothbefore microwave treatment, but after microwave treatment spores were shrinked. After microwave treatment, the solution of spore cells overflow, the result provesthat microwave treatment has destructive effect to cell membrane.