Technology

2016-12-29 14:17:12

The atmosphere in an MA package consists of N2, O2 and CO2. It is the altered ratio of these gases that makes a difference in the prolongation of shelf life.

By reducing the O2-level and increasing the CO2-level, ripening of fruits and vegetables can be delayed, respiration and ethylene production rates can be reduced, softening can be retarded and various compositional changes associated with ripening can be slowed down.

Carbon dioxide inhibits the growth of most aerobic bacteria and molds. Generally speaking, the higher the level of CO2, the longer the achievable shelf life. However, CO2 is readily absorbed by fats and water - therefore, most foods will absorb CO2. Excess levels of CO2 in MAP can cause flavor tainting, drip loss and pack collapse. It is important, therefore, that a balance is struck between the commercially desirable shelf life of a product and the degree to which any negative effects can be tolerated. When CO2 is required to control bacterial and mold growth, a minimum of 20% is recommended.

When packaging meat and fish, the high CO2-levels are effective bacterial and fungal growth inhibitors. In the case of vegetables and fruits, CO2 is not a major factor since CO2-levels above 10% are needed to suppress fungal growth significantly. Unfortunately higher levels than 10% of CO2 are working phytotoxic for fresh produce.

Nitrogen is an inert gas and is used to exclude air and, in particular, oxygen. It is also used as a balance gas (filler gas) to make up the difference in a gas mixture, to prevent the collapse of packs containing high-moisture and fat-containing foods, caused by the tendency of these foods to absorb carbon dioxide from the atmosphere. For modified atmosphere packaging of dried snack products 100% nitrogen is used to prevent oxidative rancidity.

Oxygen causes oxidative deterioration of foods and is required for the growth of aerobic microorganisms.

Generally, oxygen should be excluded but there are often good reasons for it to be present in controlled quantities including:

• Maintain fresh, natural color (In red meats for example)

• To maintain respiration (In fruit and vegetables)

• To inhibit the growth of anaerobic organisms (In some types of fish and in vegetables)

Oxygen is essential when packaging fresh fruits and vegetables as they continue to respire after harvesting. The absence of O2 can lead to anaerobic respiration in the package, which accelerates senescence and spoilage. Too high levels of O2 do not retard respiration significantly and it is around 12% of O2 where the respiration rate starts to decrease. So oxygen is used in low levels (3-5%) for positive effect.

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