Determination of film requirements and respiratory behaviour of fresh produce in modified atmosphere packaging

A simple technique was developed for determining the respiration rate of produce stored in modified atmosphere packaging (MAP) over the entire storage period including the initial time when the produce responds to the modified atmosphere. It is based on a material balance equation that relates the package film permeability and produce metabolism to the in-package gas concentrations. The equation is particularly useful for determining basic metabolic processes of produce such as respiration and ethylene biosynthesis in actual modified atmosphere packages, even when steady state conditions do not exist. Alternatively, when the respiration rate is known, the film permeability required for MAP can be determined. The work reported here shows there is significant difference between permeability values measured by the ASTM Dow cell method and the mixed gas cell method. It was found that the film permeability must be measured by a mixed gas cell method for the technique to give realistic predictions. When film permeability is determined using this method at the conditions under which the produce is to be stored, it can be used directly in the equation without any need for corrections. The material balance and permeability measurement were tested by determining the metabolic activity of broccoli (cv. 'Marathon') stored under MAP (6% CO₂, 1.5% O₂) at 1.5 °C. The steady state oxygen consumption, carbon dioxide production and ethylene biosynthesis were 8.8 ml kg^-1 h^-1, 9.0 ml kg^-1 h^-1 and 0.04 μl kg^-1 h^-1, respectively. These measurements agree with published and measured values.