Harvested fruits, vegetables and cut flowers are alive and therefore breathe oxygen, respire and give off carbon dioxide. The rate of respiration and consequential heat of respiration varies greatly from produce to produce and varies for a particular produce depending on temperature and the composition of the atmosphere around the produce.

For example, respiration rate increases with increasing temperature, increasing oxygen and the presence of ethylene gas. Respiration rate decreases with increasing carbon dioxide.These changes in respiration rate occur because living produce can sense temperature and surrounding gas composition and via a biofeedback mechanism, alter its respiration rate.

Classic examples of this include:
1.The need to store fresh produce at low temperatures to increase storage life.
2.The very strong ageing and ripening response of fresh produce to ethylene gas.
3.The standard practice of apple storage using controlled atmospheres where oxygen, carbon dioxide and ethylene gas are all controlled for several months.

Modified atmosphere packaging usually refers to the practice of imposing a particular gas composition around dead produce such as meats, cheese & bakery products.

The basic concept of "Inter-active Packaging" uses the ability of fresh produce to adjust its' respiration rate via this biofeedback mechanism. In a sense, the produce does the work so as to ramp its metabolism down from a high rate at packing to a much lower, steady rate in storage.

Whilst the application of "Inter-active Packaging" is simple, the underlying variables and mechanisms are complex. Rather than predict an outcome and force an atmosphere around the produce via a feed forward mechanism (as in Modified Atmosphere Packaging), "Inter-active Packaging" allows the produce to sort itself out via its own biofeedback mechanisms.

Normal PE, PP and PS packaging have permeability's that are too low to allow the produce to reduce its metabolism before all the oxygen surrounding the produce is consumed and the air space becomes anaerobic, leading to death of the produce. "Inter-active Packaging" provides higher gas permeability's so as to allow greater inflow of oxygen and outflow of carbon dioxide from the package surrounding the produce, thereby allowing the produce enough flexibility to modify its surrounding air so as to survive in a state of reduced metabolic activity (suspended animation).

As discussed above, there are many factors that influence the metabolism of a particular produce and these factors vary over time in a dynamic manner. Whilst it is theoretically possible to design a particular interactive film for a particular set of permeability's, this point becomes irrelevant because of the dynamic nature of the interactive process.

Fortunately, the standard smartbag covers most produce over their normal packing and storage temperature ranges with the one formulation. Problems generally only occur when storage protocols are violated (particularly with increased storage temperature which greatly increases produce mechanism).

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