Modified Atmospheric Packaging

The modified atmosphere concept for packaged goods consists of modifying the atmosphere surrounding a food product by vacuum, gas flushing or controlled permeability of the pack thus controlling the biochemical, enzymatic and microbial actions so as to avoid or decrease the main degradation’s that might occur. This allows the preservation of the fresh state of the food product without the temperature or chemical treatments used by competitive preservation techniques, such as canning, freezing, dehydration and other processes.

MAP is the replacement of air in a pack with a single gas or mixture of gases; the proportion of each component is fixed when the mixture is introduced.

The normal composition of air is 21% oxygen, 78% nitrogen and less than 0.1% carbon dioxide. Modification of the atmosphere within the package by reducing the oxygen content while increasing the levels of carbon dioxide and/or nitrogen has been shown to significantly extend the shelf-life of perishable foods at chill temperatures.

Advantages and disadvantages of MAP

Advantages of MAP:

  • Increased shelf-life allowing less frequent loading of retail display shelves;
  • Reduction in retail waste;
  • Improved presentation-clear view of product and all round visibility;
  • Hygienic stack able pack, sealed and free from product drip and odour;
  • Easy separation of sliced products;
  • Little or no need for chemical preservatives;
  • Increased distribution area and reduced transport costs due to less frequent deliveries
  • Centralized packaging and portion control
  • Reduction in production and storage costs due to better utilization of labor, space and equipment

Disadvantages of MAP:

  • Capital cost of gas packaging machinery
  • Cost of gases and packaging materials
  • Cost of analytical equipment to ensure that correct gas mixtures are being used
  • Cost of quality assurance systems to prevent the distribution of leakers, etc
  • increased pack volume which will adversely affect transport costs and retail display space
  • potential growth of food-borne pathogens due to temperature abuse by retailers and consumers
  • benefits of MAP are lost once the pack is opened or leaks

Packaging Materials: There are six main characteristics to consider when selecting packaging material for MAP foods:

  • Resistance to puncture
  • Sealing reliability
  • Anti fogging properties
  • Carbon dioxide permeability
  • Oxygen permeability
  • Water transmission rate

Although an increasing choice of packaging materials is available to the MAP industry, most packs are still constructed from four basic polymers: polyvinyl chloride (PVC), polyethylene terephthalate (PET), polypropylene (PP) and polyethylene (PE).

Machine Systems for MAP:

The first element for optimum gas packaging is appropriate equipment. There are two different techniques to replace the air:

  • Gas flushing: The gas flush technique is normally accomplished on a form fill-seal machine. The replacement of air inside a package is performed by a continuous gas stream. This gas stream dilutes the air in the atmosphere surrounding the food product. The package is then sealed. Since the replacement of air inside the package is accomplished by dilution, there is a limit on the efficiency of this unit. Typical residual oxygen levels in gas flushed packs are 2-5% O2. Therefore, if the food item to be packaged is very oxygen sensitive, the gas flush technique is normally not suitable
  • Compensated vacuum: The compensated vacuum technique removes the air inside by pulling a vacuum on the atmosphere inside the package and then breaking the vacuum with the desired gas mixtures. Since the replacement of the air is accomplished in a two-step process, the speed of operation of the equipment is slower than the gas flush technique. However, since the air is removed by vacuum and not simply diluted, the efficiency of the unit with respect to residual air levels is better. Therefore, if the food product is extremely sensitive to oxygen, a compensated vacuum machine must be used.

Application of MAP to Fruit and Vegetables

There are many advantages of MAP fruit and vegetables, but the most obvious one must be the extension of shelf-life. 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, which may be seen as chlorophyll retention, delayed softening and the prevention of discoloration. The extension of shelf-life is most noticeable with prepared products; this, combined with ease of use for the consumer, makes a MAP pack an attractive form of product presentation. Additionally, MAP packs reduce the quantity of water vapour lost from the produce.

Although fresh fruit and vegetables have been removed from the parent plant and from their normal nutrient supplies, they will continue to respire. Under normal aerobic conditions, the rate of respiration of a product may be determined by either oxygen uptake rate or carbon dioxide production rate. A high respiration rate is usually associated with a short shelf-life. When the rate of packaging film transmission of oxygen and carbon dioxide equals the rate of respiration of the product, an equilibrium concentration of both gases is established.

The equilibrium values attained depend on:

  • The respiration rate of the product
  • Fill weight of product
  • The film surface area which is available for gas exchange

The respiration rate of the product is influenced by:

  • Storage temperature
  • Produce variety
  • Growing area and conditions
  • Injury to the produce