• postharvest;
  • modified-atmosphere packaging;
  • prediction equations


To investigate free-volume changes in flexible, sealed packages containing respiring fruits and vegetables, a simple method based on the dilution of an injected gas (ethane) in the package was developed. Free-volume decreased steadily at ∼3 cm3/day after an initial transient period in low-density polyethylene packages (29-μm-thick film; 600-cm2 surface area; initial free volume ∼285 cm3) containing 40g of cut broccoli held at 0°C. A general transient model was developed that showed that free-volume changes in flexible packages were a function of differential film O2, CO2, and N2 permeabilities and differential product O2 uptake and CO2 production rates. The model predicted that flushing packages with low permeative gases would decrease free-volume depletion rate, whereas flushing with highly permeative gases, such as CO2, would increase the initial rate considerably.