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What is Modified Atmosphere Processing?

Modified atmosphere packaging (MAP) and controlled atmosphere (CA) storage modify the composition of air surrounding stored or packaged food or other perishable products. MAP and CA can slow chemical changes and microbial growth to maximize freshness without boiling, freezing, chemicals, irradiation or dehydration. 

Table of Contents

  1. What is Modified Atmospheric Packaging?
  2. Early Controlled Atmosphere Research
  3. Benefits of MAP
  4. Disadvantages of MAP
  5. Utilizing Modified Atmosphere Packaging
  6. Gases Used in Modified Atmosphere Packaging
  7. Recommended Gas Mixtures for MAP
  8. Sensors used in Modified Atmosphere Packaging

What is Modified Atmospheric Packaging?

At its simplest, MAP is the replacement of the air in a food package with a controlled mixture of gases. The normal composition of air is 21% oxygen, 78% nitrogen, 0.04% carbon dioxide and other trace gases. The atmosphere within the package is modified by reducing the oxygen content while increasing the levels of nitrogen or carbon dioxide. This has been shown to significantly extend the shelf-life of perishable foods at less than freezing temperatures.

Controlled atmosphere (CA) storage is similar to MAP in that it uses a controlled mixture of gases. However, CA is generally used to describe mixtures of gases in bulk storage bins, refrigerators, containers or silos.

Early Controlled Atmosphere Research

Ancient Chinese writings report transporting fruits in sealed clay pots with fresh leaves and grass to generate a low-oxygen and high CO2 atmosphere. Some scholars have argued that the pharaoh’s storage of grain described in the Old Testament is an example of CA storage of grain. However, one of the first published demonstrations of CA was in 1821, when Jacques Berard in France showed that fruit placed in sealed containers without oxygen did not ripen.

Although there were similar experiments over the next 100 years, in 1917 Franklin Kidd and Cyril West in Cambridge, England set to work extensively researching the use of “gas storage” at the behest of the British Government with the goal of preserving fresh food during the First World War. After visiting Kidd and West, in 1938 Robert Smock from Cornell University set to work improving the storage life of the newly popular McIntosh variety of apples in the United States. Smock coined the term “controlled atmosphere storage” as he felt it better described the technology that the term “gas storage” used by Kidd and West.

Smock continued to experiment with various gas levels for different fruits and vegetables. He published dozens of papers throughout his lifetime, and along with Kidd and West their research has formed the foundation of CA storage techniques used today.

In addition to fruits and vegetables, MAP and CA is used in the meat and poultry industries, for baked goods, pasta, dairy products, dried foods and for drug packaging.

Benefits of MAP

The shelf-life of fresh and dried packaged foods is limited by the growth of micro-organisms over time. However, even before food becomes dangerous for consumption, changes in odor, flavor and color will make the food less attractive for sale. The principal benefit of MAP is longer shelf life. The shelf life of the packaged products can be extended by 50–200% by using MAP.

For example, lowering the oxygen concentration below 8% has been shown to have a significant effect on fruit ripening, while adding carbon dioxide above 1% can improve results. These benefits occur even at higher temperatures, which reduce the requirement for chilling fruits such as tomatoes, melons and bananas which are sensitive to freezing.

Because of the longer shelf life, fresh produce stored in modified atmosphere packaging has the additional advantage of less product waste. Longer shelf life improves profitability. In addition, food can be transported longer distances, allowing consumers to enjoy products that may not be available locally or in season.

This article from the Guardian “Just how old are the 'fresh' fruit & vegetables we eat?” gives an interesting description of the use of CA storage and MAP of many common fruits and vegetables we eat.

Disadvantages of MAP

The primary disadvantages of MAP are cost and complexity. The equipment required to accurately modify the gases inside sealed packages or to create sealed storage areas for CA requires a significant investment. The extended shelf-life must be weighed against the cost.

Another potential disadvantage of MAP is the reaction of the packaging film to increased temperatures. Undesirable consequences of incompatible film and/or high temperatures may be anaerobic respiration with the accumulation of acetaldehyde, ethanol, ethyl acetate, or lactic acid contributing to the development of bad odors or flavors. In addition, different kinds of packaging films have different gas permeability. Therefore, the proper film must be matched with the product being stored.

Utilizing Modified Atmosphere Packaging

There are many steps in transporting food from farms to the table. In general, the sooner MAP or CA is accomplished, the greater the benefit. There are three places it is utilized.

Bulk-storage after harvest - In the case of apples, bulk containers are loaded into cold storage rooms where the fruit’s respiration rate is slowed. Fruit for imminent consumption is chilled, while fruit for longer term consumption is placed in controlled atmosphere (CA) storage with oxygen levels lowered from 21% to 1.2%, putting the apples to sleep for 6-12 months.

During transport. In cases where the produce has to travel long distances, it can be loaded into sealed bulk containers where the oxygen level is lowered for long-distance transport. When combined with cooling, this makes it possible to transport fresh produce worldwide in cargo container ships.

During packaging. During food packaging, the package (bag, bottle, carton, etc.) has any remaining air space in the package replaced using a jet of modified air of a known concentration. At the moment the normal oxygenated air is purged, the package is sealed. In a high-speed production environment, this fill, purge and seal cycle can happen hundreds of times per minute.

In bottling beer for example, a drop of liquid CO2 or nitrogen is added to the bottle/can just before capping. As the gas expands, it pushes out the air and oxygen in the head space.  Once sealed, the vessel becomes pressurized by the carbonated liquid in the bottle or can thus allowing the ever familiar "psst" sound when you open your beverage.

Gases Used in Modified Atmosphere Packaging

MAP applications use a combination of nitrogen, carbon dioxide and carbon monoxide to replace oxygen, or in the case of fruits and vegetables, to reduce the amount of ethylene (C2H4) given off by the produce. Oxygen encourages the growth of aerobic spoilage microorganisms. Ethylene is a growth-stimulating hormone produced by fruits and vegetables during storage. Ethylene build-up speeds up respiration rates and reduces shelf-life.

  • Oxygen is the most important gas to be reduced in MAP. In general, the lower the oxygen level, the longer the shelf-life of the product. Oxygen levels approaching 0% are common. The exception is fruit and vegetable storage where oxygen is required for respiration, and in meat packaging where oxygen is required to retain the color of red meat.
  • Carbon dioxide is useful at controlling bacterial growth. For products like hard cheese, bakery products and carbonated beverages the CO2 level can approach 100%.
  • Nitrogen is a commonly used to displace oxygen in MAP because it of its low solubility in in water and fat. It is also used in products like potato chip packages to prevent package collapse.
  • Carbon monoxide is effective in maintaining the red color in fresh meat, and reduces the browning of lettuce in bagged salads. CO storage is not used in many countries. However, it is used in up to 70% of packaged meats in the US. The FDA has concluded it is safe at levels up to 0.4%
  • Other gases. Depending on the product, microbial growth can also be inhibited with trace amounts of nitrous oxide (N2O), argon (Ar) and hydrogen (H2).

Recommended Gas Mixtures for MAP

Product % Oxygen % CO2  % Nitrogen
Red meat 60-85 15-40 -
Red meat US * - 30 70
Cooked meat - 20-35 65-80
Poultry - 25 75
Hard cheese - 100 -
Soft cheese - 30 70
Bread - 60-70 30-40
Fruits & vegetables 1-5 2-15 80-95
Dried foods, chips, etc. - - 100
Beer, carbonated beverages - - 100

* In the US red meat is commonly packaged with 0.4% carbon monoxide gas.

Sensors used in Modified Atmosphere Packaging

To test the effectiveness of the modified atmosphere, manufacturers will either continuously test the oxygen content in real time during package sealing, will select every X package off the production line for statistical analysis, or both.

sample testing

The TecPen Handheld 0-5% Oxygen Sensor is designed to provide accurate measurements of oxygen content in all closed and pierce-able food packaging containers.

For spot testing of CO2 levels, we offer CO2 sampling data loggers that can measure from 5% up to 100% CO2.

Manufacturers who want to create MAP solutions like head-space monitoring of beverages have used our oxygen sensors as well as our CO2 sensors. For ultra-high speed applications, we have designed ring-arrays of CO2 sensors for OEM manufacturers capable of making 10 measurements per second.

Resources

Thompson, A. Prange, R. (2019). Controlled Atmosphere Storage of Fruit and Vegetables, 3rd Edition. CABI Press.

Kader, A. Zagory, D. Kerbel, E. (1989). Critical Reviews in Food Science and Nutrition, Vol.28, Issue 1

Parry, R.T. (2012). Principles and Applications of Modified Atmosphere Packaging of Foods. Springer Science & Business Media.

Bodbodak, S. Moshfeghifar, M. (2016). Advances in modified atmosphere packaging of fruits and vegetables. Eco-Friendly Technology for Postharvest Produce Quality, pp. 127-183. Academic Press.

Modified Atmosphere Packaging. Wikipedia.org


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