Design of modified atmosphere packaging systems for fresh produce

Methods and procedures were developed for predicting, testing, and optimizing modified atmosphere packaging (MAP) designs for fresh produce. Appropriateness of a MAP design for a commodity can be evaluated rapidly by predicting the in-package steady state O$\sb2$ concentrations with prediction equations. Input variables needed for the development of prediction equations are: (1) film permeability to O$\sb2$ (Po$\sb2$), (2) commodity O$\sb2$ consumption rates for different O$\sb2$ concentrations (RRo$\sb2$), (3) film surface area (A), and (4) produce weight in package (W$\sb{\rm p}$). A steady state method was developed for rapid and accurate measurements of Po$\sb2$. Repeated measurements of the Po$\sb2$ for two different polyethylene + ethyl-vinyl acetate additive (PEVA) films used in this study yielded coefficients of variation less than 3%. RRo$\sb2$ was derived from quadratic regression equations fitted to the O$\sb2$ depletion data. The final predictive equations were used to predict steady state O$\sb2$ concentrations in various designs of MAP for tomato (Lycopersicon esculentum Mill. \u27Heinz 1370\u27), cabbage (Brassica oleracea L. capitata \u27Express\u27), and muskmelon (Cucumis melo L. var. reticulatus Naud. \u27Mission\u27). Predicted steady state O$\sb2$ concentrations in MAP of tomato (Po$\sb2$ = 0.0426 and 0.0620 ml.cm$\sp{-2}$.hr$\sp{-1}$.atm$\sp{-1}$, A = 700 to 1350 cm$\sp2$, W$\sb{\rm p}$ = 85 to 1400 g) and in MAP of cabbage (Po$\sb2$ = 0.03 ml.cm$\sp{-2}$.hr$\sp{-1}$.atm$\sp{-1}$, A = 3600 cm$\sp2$, W$\sb{\rm p}$ = 1500 to 4500 g) were in most cases within 10% of those measured experimentally. For muskmelon, predicted steady state O$\sb2$ concentration were 2% to 3% higher than those achieved experimentally. Procedures were refined by developing the RRo$\sb2$ from a steady state experiment. This refinement significantly improved prediction results as indicated by a reduction of % error of predicted from experimental from 46% to 20%. A rapid method for testing predictions or packaging designs is to use a technique of active modification of atmospheres. The desired O$\sb2$ concentration within packages and commodity tissues was established in less than 20 minutes, and subsequent maintenance or deviation of the actively established O$\sb2$ concentration from a target O$\sb2$ concentration can then be used to evaluate the package design or the accuracy of predictions. This research indicated that an appropriate design of MAP for a commodity can be achieved efficiently by predictions of steady state O$\sb2$ concentrations for a wide range of packaging variables. Rapid confirmations or refinements of packaging designs can be achieved with a small scale active modification technique