Active Packaging

Active packaging can use oxygen scavengers, carbon dioxide scavengers or emitters, chemically treated films, temperature-controlled packages, or time-and-tempera-ture controlled packages (14). To insure early attainment and maintenance of continuous zero-oxygen concentrations in MAP, oxygen absorbers or scavengers can be added to the package to actively remove residual oxygen and oxygen that permeates the packaging film. The most common oxygen scavengers are reduced-iron powders mixed with acids, salts, or both to oxidize in the presence of oxygen. Most scavengers need to be activated by some wetted humectant (13). When a wetted humectant was added to the scavenger and placed in an aerobic atmosphere, oxygen scavenging occurred at near maximum rate (15). A scavenger used in an ultra-low-oxygen system can quickly lower oxygen levels below limits of detection.

AgelessĀ® (Mitsubishi, Japan), a scavenger widely used by the food industry, has iron powder in a small packet that is highly permeable to oxygen. According to Nakamura and Hoshino (16), 1 g of iron can react with 0.0136 mol of oxygen, producing ferrous oxide. One gram or about 0.7 L of oxygen reacts with about 300 cm3 of oxygen scavenger at standard pressure and temperature. Packets are available in sizes ranging from 20 to 2,000 cm3 in oxygen-scavenging capacity. To remain within the scavenging ability of an oxygen scavenger, the barrier film permeability must be <20 cm3/cm2/24 hours, and the advantage of minimal oxygen to be scavenged is important.

An active packaging system (Cryovac OS 1000) released in 1998 (17) uses a polymeric oxygen-scavenging system that absorbs oxygen within the MAP package, and the polymer also serves as an oxygen barrier. The proprietary oxygen-scavenging layer consists of three primary components: an oxidizable polymer, a photoinitiator (PI), and a catalyst. The oxidizable polymer is the component responsible for binding the oxygen molecules. The PI absorbs the UV light and provides the energy to start the reaction. The catalyst helps to increase the rate of the scavenging reaction. The advantage of this system is that it is activated by UV light quickly after the package is sealed and does not require injection of an activating fluid.

An earlier stumbling block of sachet-type scavengers was a desire, especially by marketing people, not to have this "foreign material" in the final retail package. Some newer applications avoid this problem by attaching the iron-filled sachet to the outer barrier dome or bag, so it is disposed of and never appears with the final retail package. Most scavengers work more slowly at the low temperature required for chilled meat. This presents a problem as rapid scavenging of oxygen is a must for ultra-low-oxygen applications if rapid blooming is anticipated upon later exposure to air.

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