Theoretical And Experimental Research On Modeling Of Modifled Atmosphere Packaging For Spinacla Oleracea L

Modified atmosphere packaging (MAP) is a well-established technology that can inhibit the respiration rate and metabolic activity of fruits and vegetables, which helps maintain the quality and extend the shelf-life of the perishable produce. In order to provide theoretical support for MAP design of spinach (Spinacia oleracea L.), four parts were studied in this paper:1. The permeability coefficients of LDPE film at5℃,10℃,15℃,20℃and25℃were calculated by injecting gas to the film bags. The influences of temperature on permeability coefficient and permeability coefficient ratio were also analyzed. The results suggested that the permeability coefficient of LDPE film increased with temperature; furthermore, increase in temperature could enhance the permeability coefficient ratio significantly. The relationship between permeability coefficient and temperature was well described by the Arrhenius equation, i.e. a linear relationship between the natural logarithm of permeability coefficient and the reciprocal of thermodynamic temperature.2. The respiratory characteristics of spinach were studied at different experimental temperatures. The headspace composition, in terms of O2and CO2concentrations, in air-tight jars and LDPE film packages of spinach at5℃,10℃,15℃,20℃and25℃were monitored, respectively. The respiration rates of spinach were then calculated respectively by using the calculation equations and a C program for the two methods of measurement. Results showed that the respiration rate of spinach was directly proportional to temperature and O2concentration, but inversely proportional to CO2concentration. The rates of CO2evolution were lower than that of O2consumption, and the inhibition behavior of CO2was uncompetitive with O2during the respiration of spinach. Relationship between temperature and the initial respiration rate of spinach was also found in accordance with the Arrhenius equation.3. The theories and methods related to biostatistics, enzyme kinetics, and chemical kinetics were respectively adopted to develop respiration rate models, obtaining the second-order polynomial equations, Michaelis-Menten equations with uncompetitive mechanism, as well as chemical kinetics equations. The model parameters were estimated by fitting the models to the experimental data by linear or non-linear regression. The performances of the three types of respiration rate models of spinach were validated at3℃and12℃. Results showed that both the maximum respiration rate of Michaelis-Menten equation and the rate constant of chemical kinetics equation were found following the Arrhenius relationship with temperature, respectively. The respiration rate models based on chemical kinetics, which could easily incorporate the effects of temperature, O2concentration and CO2concentration on the respiration rate, were of good prediction accuracy and yielded a satisfactory prediction result to predict the respiration rate of spinach, significantly better than the other two types of models.4. Respiration rate model can be used for designing MAP of fruits and vegetables. Taking the factors such as temperature, gas composition, thickness and area of polymeric film, product weight within package into account, combined with the respiration rate models based on the chemical kinetics, an example of selecting appropriate packaging films for spinach was given to explain the application of respiration rate model.