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  • Author or Editor: Sannai Gong x
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Procedures for predicting optimum packaging conditions of modified atmosphere packages (MAP) of tomato (`Heinz 1370') were developed. The relationship between O2 consumption rate and O2 concn (RRo2) was determined using O2 depletion data collected by enclosing tomatoes in jars and sampling head space O2 concn over time. The fitted function was then used in conjunction with other input variables: (1) film permeability to O2 (PO2), (2) film surface area (A), and (3) fruit weight in packages (Wp) to develop the final predictive equation based on Fick's law of gas diffusion. Predictive power of the equation was tested by comparing the steady state O2 concn achieved experimentally with those predicted for a wide range of packaging conditions. Packaging conditions included film surface area, weight of fruit in packages, and O2 permeability of the film (0.0426 and 0.0620 ml/kg hr). Prediction curves showing steady state O2 concn vs. packaging ratio (A/Wp) closely resembled the best fit curves of data. The effect of temperature on steady state O2 concn in MA bags was also examined. Increasing temperature from 20°C to 28±2°C had little effect but decreasing temperature to 10°C led to higher in-package O2 concn. Results indicate that predictive equations can be used to select appropriate films and optimize packaging ratios to achieve desired steady state O2 concn for MAP of tomatoes.

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A rapid steady state method for measurement of gas permeability of polymeric films was developed. Films were sealed between two equal volume chambers with pure O2 and pure N2 flowing through opposite sides. Oxygen concentration in the N2 cell was measured over time until steady state was reached. The method was used to determine oxygen permeability of two different films. Results from four replications on each film indicated excellent repeatability with coefficients of variation less than 3%. The time required to reach steady state oxygen concentration was dependent upon film type, flow rate, and temperature. The higher the N2 flow rate the shorter the time to reach steady state O2 concentrations. The slowest measurement at the lowest flow rate of 27 ml/min took less than 3 hours to collect the data necessary to achieve steady state. Increasing temperature from 10°C to 20°C resulted in an approximately 40% increase in O2 permeability for both films tested. The technique will be a valuable tool for measuring permeabilities of new films and the same film at different temperatures, and for selecting the appropriate material for modified atmosphere packaging of fresh produce.

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It frequently takes days to weeks for testing films to determine if desired steady state concn of gases are reached when atmospheres are passively modified through commodity respiration. Our objective was to develop a rapid method to test the appropriateness of packaging films and designs using active modification of the atmosphere. Repeated exposures of commodities to partial vacuum were followed by infusion of N2 to 1 atm. Three to five minutes were allowed following each N2 infusion. Initial O2 concn achieved in packages (polyethyl vinyl acetate) depended upon the extent of the vacuum and the number of exposures. Within packages of tomatoes, O2 concn of 8.3 ± 0.5% and 5.0 ± 1.0% were measured following exposure to 460 and 360 mm Hg vacuum, respectively. Three exposures of cabbage and muskmelon packages to 460 mm Hg resulted in O2 concn of 5.1 ± 1.4% and 5.0 ± 1.4%, respectively. Maintenance or deviation from actively established atmospheres was determined within hours.

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Mathematical procedures for predicting steady-state O2 concentrations for a range of packaging conditions for modified-atmosphere packages (MAP) of `Heinz 1370' tomato (Lycopersicon esculentum) were developed and tested. The relationship between O2 consumption rate and O2 concentration was determined using O2 depletion data collected by enclosing tomatoes in jars and sampling head space O2 concentration over time. The fitted function was then used in conjunction with the input variables film permeability to O2 (PO2), film surface area (A), and fruit weight in packages (Wp) to develop an equation to predict steady-state O2 concentrations for different packaging ratios (A/Wp) and film permeabilities. Prediction curves showing steady-state O2 concentration for packaging ratios in the range of 1 to 12 closely resembled best-fit curves of experimental data. Increasing temperature from 20 to 28C had little effect on in-package O2 concentration, but decreasing temperature from 28 to 10C led to higher in-package O2 concentrations. The predictive equation developed can be used to select appropriate films and optimize packaging ratios to achieve desired steady-state O2 concentrations for MAP of tomatoes.

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It frequently takes days or weeks to determine if desired steady state concentrations of gases are reached in modified atmosphere packages of produce when atmospheres are modified by commodity respiration. We present a rapid method for testing packaging films and designs with active modification of atmospheres by vacuum and N2 infusion. Reduction of O2 concentration in produce packages and commodity tissues was completed within minutes by using several cycles of vacuum and N2 infusion treatments. Produce packages were placed in a desiccator and subjected to repeated partial vacuums, each followed by infusion of N2 to one atmosphere. Resulting O2 concentrations in packages (polyethylene + ethyl-vinyl acetate additive) were dependent on the extent of vacuum and the number of evacuations. Within packages of tomatoes, O2 concentrations of 8.3% ± 0.5% and 5.0% ± 1.0% were measured following two evacuations at 460 and 360 mm Hg, respectively. Three evacuations of cabbage and muskmelon packages at 460 mm Hg resulted in O2 concentrations of 5.1% ± 1.4% and 5.0% ± 1.4%, respectively. Maintenance or deviation from actively established atmospheres by the film was determined within hours.

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