Effect of Hydrodynamic Conditions and Geometric Aspects on the Permeance of Perforated Packaging Films

Modified atmosphere packaging (MAP) is applied to extend the shelf life of fresh and minimally processed produce. Commonly used films, such as oriented polypropylene (OPP), are too impermeable to gases for successful MAP for products with moderate to high respiration rates, which has led to perforated systems. In order to design the perforation profile to ensure MAP targets for extended shelf life, it is necessary to evaluate which parameters affect the mass transfer through the perforations significantly. Perforations (270 μm, 450 μm and 750 μm diameter) were made in an OPP film under different temperatures and circulating air velocities, considering also different locations for the perforations. The results obtained showed that the perforation diameter is the most important parameter and can even be more significant than the total area of perforation (and therefore the number of perforations). Air velocity around the package and storage temperature were also relevant. Stacking during storage risks blocking perforations and therefore it is recommended to pierce trays on the sides in order to ensure better robustness. The package gas composition itself also affected mass transfer due to the interplay of oxygen flux with other gas fluxes, with particular relevance to the case of water vapour.