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Prepackaging or retail packaging of certain commodities in specially designed consumer packages has the following advantages:
Deterioration or decay is decreased because the prepackages create a micro-climate with a lower oxygen and a higher carbon dioxide level and a higher relative humidity is reached. Too high a relative humidity, however, can lead to sprouting of roots and tubers and low oxygen levels will decrease respiration to such a level that produce will suffocate and rot.
In general, leafy vegetables require a high relative humidity level to prevent wilting and only a few holes in the package are recommended. Root crops require more holes, or even the use of nets as packaging material because too high relative humidities or too low oxygen levels cause sprouting.
Moulded trays, wrapped with film liners, combine four to six units (citrus, apple, etc.) to one larger unit. The tray will give the produce protection from the bottom side and some protection on the sides. The top will only be properly protected when the larger units are properly stacked.
Most commonly used materials are low-density polypropylene for bagging, regenerated cellulose or cellophane for overwrapping the trays and polyvinyl chloride film for overwrapping trays.
Polyethylene and polypropylene have a low permeability for gases and vapour and it is necessary to make holes in the bags. Other materials have higher permeabilities or permeabilities for only one of the gases or vapour and even between different brands of the same material are differences in permeability. It is recommended to purchase film material suitable for a certain commodity and to test this film material first on a small scale.