MODIFIED ATMOSPHERIC PACKAGING

Introduction:

Isn't it interesting to know that Injecting a gas increases the product's shelf life and offers extra protection, which prevents the product from discolouration. Usually, a mixture of nitrogen (N2) and carbon dioxide (CO2) is used. Dioxygen (O2) can also be added to this combination. The use of argon (Ar) has been increasing, as this contains the same properties as nitrogen (N2). It is the practice of modifying the composition of the food packages' internal atmosphere to improve the shelf life of a product. It is a kind of replacement of air in a pack with a single gas or mixture of gases; where each component's proportion is fixed when the mixture is introduced. No further control is exerted over the initial composition. The gas composition is likely to change with time due to the diffusion of gases into and out of the product.

Need for MAP:

Oxygen produces lipid oxidation reactions. It also causes high respiration rates in fruit and vegetables, leading to shortened shelf life. The presence of oxygen encourages the growth of aerobic spoilage microorganism and the potential formation of other unwanted microorganisms may also occur.

By reducing oxygen and replacing it with other gases, we can reduce or delay unwanted reactions. So, to change a package's atmosphere, the oxygen contained within must be reduced or removed. Thus, the MAP process lowers the volume of oxygen contained within the empty space of the packaging containing the product or Oxygen is often replaced with other gases.

Gases used in MAP:

1. Oxygen (O2): Food deteriorates due to physical, chemical and microbiological factors. For these reasons, in modified atmosphere packaging, oxygen is either excluded or the levels set as low as possible. The exceptions occur where oxygen is needed for fruit and vegetable respiration, colour retention as in red meat, or to avoid anaerobic conditions in whitefish. One of the significant functions of O2 in MAP meats is to maintain myoglobin in its oxygenated form, oxymyoglobin. This is the form responsible for the bright red colour, which most consumers associate with fresh red meat In MAP, oxygen levels usually are set as low as possible to reduce oxidative deterioration of foods.

2. Carbon dioxide (CO2): Carbon dioxide has bacteriostatic and fungistatic properties. There have been many theories regarding how CO2 exerts its influence on a bacterial cell. These can be summarized as follows:

a) Alteration of cell membrane function, including effects on nutrient uptake and absorption. b) Direct inhibition of enzymes or decreases in the rate of enzyme reactions. c) Penetration of bacterial membranes, leading to intracellular pH changes. d) Direct changes to the physio-chemical properties of proteins.

3. Nitrogen (N2) : Nitrogen is an inert, tasteless gas, which displays little or no antimicrobial activity on its own. However, because of its low solubility in water and fat, the presence of N2 in a MAP food can prevent pack collapse. In foods such as nuts, removing oxygen to <%1 by nitrogen flushing helps prevent oxidative rancidity of fats. Nitrogen can also indirectly influence the microorganisms in perishable foods by retarding the growth of aerobic spoilage organisms

4. Noble gases : He, Ne, Ar and Xe are the members of this group. Ar is the main gas used in MAP,it can replace nitrogen to fill in wine bottleneck before corking, can prevent growth of the microorganism in foodstuff such as broccoli and lettuce.

Modification techniques:

1. Gas flushing: During a gas flush process, a harmless gas (usually nitrogen) is actively pumped into the bag before sealing to displace ambient oxygen. This is done to decrease the amount of oxygen inside the package, which will in turn decrease the rate of spoilage, as oxygen is one of the top killers of freshness.

2. Barrier films: Plastic films and foils are used to seal the MAP food packaging. Once Nitrogen or other gas flushes the Oxygen out from the package, the barrier film protects the food from further involvement with Oxygen.

3. On-package valves: One-way valves added to the exterior of packaging are another example of MAPallow certain gases to escape from the package without allowing any outside gases in. This is often done to release pressure from off-gassing, which is when products release gases or other compounds. Most often used in the coffee industry

4. Scavenger or desiccant packs: Another example of MAP packaging is adding an oxygen scavenger or desiccant pack to the packaging. These small sachet-type packages often contain a mixture of iron powder and ascorbic acid, and sometimes activated carbon. These ingredients act as catalysts or activators, absorbing ambient moisture and oxygen, thereby removing it from the packaging

Conclusion:

There are many advantages of MAP in fruit and vegetables, but the most obvious one must be shelf life extension. By decreasing the amount of available oxygen to the produce, the respiration rate and the rate of all metabolic processes are correspondingly decreased. This results in delayed ripening and senescence. Challenges in MAP includes the cost of packaging material, storage temperature and specific gas composition for a specific product. Every technology has its own pros and cons, and hence balance has be achieved in such a way that can assure safety and quality.