Theoretical And Applied Study On Microporous Modified Atmosphere Packaging

With the improvement of living standards,more and more consumers prefer quality rice packaging.To keep rice much fresher,packaging materials of rice are demanded a lot.Microporous membranes have become a new choice due to their good permeability,waterproofness,adjustable ventilation rate,lower processing cost etc.The study adopts PA/RCPP packaging films provided by JPNC,chooses rice of Dongqi as the research object,analyzes microporous membrane's permeability mechanism,chooses proper punching parameters for rice microporous packaging.When the relevant performances of 5kg rice packaging bags are compared comprehensively on the market,their thicknesses are 120?160?m generally.The PA/RCPP membrane used in this study is 120?m thick.Based on the analysis of different samples'mechanical property,packaging bags whose tensile strength exceeds 25Mpa can meet the tensile strength of 5kg rice.Based on the permeability analysis,modified atmosphere packaging requires a high level of permeability.Common packaging materials on the market can not meet the requirement of rice respiration intensity.Therefore,some surface micro-treatments,like punching,can be used to adjust its permeability rate,?(PCO2/PO2);based on Fick theory,the permeability mechanism of microporous membranes' modified atmosphere packaging would be studied,the outside-inside gas exchange math model of rice microporous membranes would be set up,Matlab software would be used to predict and stimulate gas components' concentration change rules for some time.Experimental results and predicted curves are compared to correct math model.According to different apertures and hole quantity,the confirmatory experiment is divided into four groups,147?m/30 items(Y1),180?m/20 items(Y2),180?m/30 items(Y3),250?m/20 items(Y4).The results show:when the effective hole length is Lh=Lf+1.1r,the deviations between the four theoretical values and the four real values of O2 concentrations within the packaging are respectively 8.23%,9.81%,9.64%,11.58%.The deviations between the four theoretical values and the four real values of CO2 concentrations within the packaging are respectively 5.54%,6.42%,8.22%,8.49%.When the static sealing system is used to test rice respiratory rates under 28? 38?,48?,Michaelis-Menten equation is adopted to show rice respiratory rate,multiple linear regression method is used to get the parameters of Michaelis-Menten equation by Origin 9.0.Visual Basic software adopts BASIC language for programming.Many factors which have an influence on rice microporous packaging would have the optimal design to predict the most appropriate punching areas under different packaging parameters.The unpunched ordinary packaging would be adopted for contrast test(Z0).Microporous packaging bags whose punching parameters(apertures/hole quantity)are respectively,75?m/6 items(Z1),95?m/4 items(Z2),145?m/2 items(Z3)are used for rice packaging.The change of rice moisture content,fatty acid value,reducing sugar content would be measured under different packaging methods.The experiment results show:during the whole storage process,rice moisture contents increase respectively by 3.16%,2.58%,1.78%,1.9%,rice fatty acid value(mgKOH/100g dry basis)increase respectively by 15.16,14.56,12.59,15.94,rice reducing sugar content increase respectively by 0.2%,0.24%,0.22%,0.3%under different packaging methods.The results show:since gas exchange rate inside and outside ordinary packaging is lower,pre-configured gas ratio can be kept for some time.So all quality indexes change stably in early storage.But over time,microporous packaging can make excess water in the bag volatilized better,control the gas ratio in bag better,improve the rice freshness performance.The study values the permeability mechanism of microporous membranes,confirms the relationship between microporous effective length and real length based on experiments,combines measurement and characterization of rice respiratory rate to set up the outside-inside gas exchange math model of rice microporous membranes'modified atmosphere packaging.The model can reflect gas dynamic changes within microporous packaging to some extent.Then rice microporous packaging design program would be set up.Relevant parameters of rice microporous packaging(surface area,thickness,permeability of membrane,weight of rice,environmental parameters)would be input.Namely,the most appropriate punching areas of rice microporous packaging and the corresponding punching plan would be obtained under the corresponding packaging parameters.Compared with rice quality index of unpunched ordinary packaging,the microporous packaging microporous packaging can make excess water in the bag volatilized better,control the gas ratio in bag better,improve the rice freshness performance.