Modified Atmosphere Packaging (MAP)

Modified atmosphere packaging (MAP) is a food preservation technique in which the gaseous environment surrounding a food product inside a sealed package is altered from the composition of normal air — approximately 78% nitrogen, 21% oxygen, and 0.04% carbon dioxide — to a gas mixture tailored to slow microbial growth, reduce oxidation, and extend shelf life. The technique is a form of food preservation that does not apply heat or pressure; instead, it manipulates the biochemical and microbiological environment of the packaged food.

MAP is distinct from controlled atmosphere storage (CAS), in which the gas composition is continuously monitored and adjusted throughout bulk cold storage (as in apple warehouses). In MAP, the modified atmosphere is established at the point of packaging and remains static — or shifts passively due to product respiration — throughout distribution and retail.

Historical background

The earliest scientific documentation of atmosphere modification to extend food quality dates to 1821, when the French chemist Jacques Étienne Bérard reported that fruit stored under low-oxygen conditions exhibited delayed ripening and extended shelf life. Practical use of CO₂ in bulk ship holds to preserve meat during refrigerated ocean transport began in the 1930s.

Large-scale commercial MAP for retail products developed during the 1970s and 1980s alongside advances in flexible barrier film technology and form-fill-seal packaging machinery. By the 1990s, MAP had become a standard preservation method across fresh meat, fish, bakery, and ready meal categories in European and North American retail.

Active gases and their roles

MAP uses three primary gases, singly or in combination:

Oxygen (O₂)

Oxygen is paradoxical in MAP: it is the primary driver of aerobic microbial growth and oxidative rancidity, yet it is deliberately included in high concentrations in some applications.

• High-O₂ MAP for red meat (70–80% O₂): Myoglobin in fresh red meat requires oxygen to remain in its oxygenated form (oxymyoglobin), which is the bright red colour consumers associate with fresh meat. Without oxygen, myoglobin converts to metmyoglobin (brown). High-O₂ MAP maintains the oxymyoglobin state and thereby the red colour throughout the retail display period.
• Low-O₂ or zero-O₂ MAP: For many other products — fish, cooked meats, cheese, bakery, snack foods — oxygen is excluded entirely to suppress aerobic spoilage and oxidation.
• Low-O₂ MAP for fresh produce (2–5% O₂): Respiring fruits and vegetables require some oxygen to sustain aerobic metabolism. Reducing oxygen below 2% can trigger anaerobic fermentation, producing off-flavours; levels of 2–5% slow respiration and senescence while avoiding fermentation.

Carbon dioxide (CO₂)

Carbon dioxide is the primary antimicrobial gas in MAP. Its mechanism of action involves dissolution in the aqueous phase of food to form carbonic acid, which lowers intracellular pH in bacteria, inhibits bacterial enzymes, and disrupts membrane permeability. CO₂ is most effective against aerobic spoilage organisms including Pseudomonas spp., Brochothrix thermosphacta, and many moulds.

Key constraints on CO₂ use:

• CO₂ is highly soluble in fat and water; it dissolves into the food during storage, which reduces package headspace and can cause flexible packs to collapse inward (a phenomenon sometimes misread by consumers as product spoilage). Nitrogen is commonly added as a filler gas to prevent this.
• Concentrations above 10% are phytotoxic to most fruits and vegetables, causing tissue damage, accelerated browning, and off-flavours.
• Very high CO₂ (60–100%) is appropriate for fish, which tolerates higher concentrations and benefits from strong antimicrobial action against the Gram-negative spoilage flora typical of fish.

Nitrogen (N₂)

Nitrogen is an inert filler gas used primarily to maintain package integrity. It does not react with food constituents or microorganisms. Its role is to:

• Replace oxygen in the headspace without the phytotoxicity or absorption issues of CO₂
• Prevent package collapse when CO₂ dissolves into the product
• Displace oxygen in applications such as coffee, nuts, and snack foods where oxidative rancidity is the primary quality concern

In fresh pasta and some dried products, nitrogen alone (100% N₂) is sufficient when oxidation and aerobic microbial growth are the only concerns.

Standard gas compositions by product category

Gas compositions are not universal; they are optimised for each product’s microbiology, biochemistry, and consumer expectations:

Packaging materials

The effectiveness of MAP depends entirely on the barrier properties of the packaging material. Film permeability to O₂, CO₂, and water vapour determines how long the modified atmosphere is maintained.

Barrier films

High-barrier films are required for most MAP applications to prevent gas exchange with the external atmosphere:

• Ethylene vinyl alcohol (EVOH): excellent O₂ barrier; widely used in multi-layer laminates
• Polyvinylidene chloride (PVDC): high barrier to O₂, CO₂, and water vapour
• Polyamide (nylon): good O₂ barrier, puncture-resistant; used in meat and fish applications
• PET (polyethylene terephthalate): moderate barrier, commonly used as outer layer in laminate structures

Most commercial MAP films are multi-layer co-extrusions or laminates combining a gas barrier layer, a structural layer, and a heat-sealable inner layer.

Permeable films for fresh produce

Fresh fruits and vegetables continue to respire after harvest, consuming O₂ and producing CO₂. If sealed in an impermeable film, O₂ is rapidly depleted and CO₂ accumulates to damaging levels. Permeable micro-perforated films or films with controlled gas transmission rates allow passive equilibrium to be reached between the product’s respiration rate and the permeability of the film — this is the basis of equilibrium modified atmosphere (EMA) packaging.

Selecting the correct film permeability requires matching the film’s O₂ transmission rate (OTR) to the respiration rate of the specific product at the intended storage temperature. Companies such as Perfotec (Netherlands) specialise in film perforation systems and software to calculate the optimal OTR for specific produce types and pack formats.

Rigid trays

Thermoformed rigid or semi-rigid trays sealed with a barrier lidding film are commonly used for meat, fish, and ready meals. Thermoforming allows in-line packaging on form-fill-seal machines. Tray materials include PP (polypropylene), PET, and CPET (crystallisable PET, for ovenable trays).

Equipment

Three main equipment categories are used for MAP:

Form-fill-seal (FFS) machines

• Horizontal FFS (flow-wrap): a roll of film is formed into a tube around the product, sealed at the bottom and ends; the gas flush occurs before the final seal. Used for small packs of bakery, snack products, and fresh produce.
• Vertical FFS: product is dropped vertically into the formed film tube; used for powders, small items, and loose salads.
• Thermoform-fill-seal: the lower film is thermoformed into trays in-line, filled with product, gas-flushed, and sealed with lidding film. Used for meat, fish, and ready meals.

Chamber machines

Batch machines in which the entire package is placed inside a chamber, the chamber is evacuated, the modified atmosphere gas is injected, and the package is sealed while the atmosphere is in the chamber. Higher precision than snorkel flushing; used for premium applications.

Snorkel machines

A nozzle (snorkel) is inserted into the opening of a pre-formed bag to flush gas before heat-sealing. Simpler and less capital-intensive than chamber or FFS systems; used for artisan and small-scale production.

Shelf life extension

MAP extends refrigerated shelf life by suppressing the microbial and biochemical deterioration mechanisms that limit fresh food quality:

Shelf life figures depend on raw material quality, processing hygiene, storage temperature, and gas composition — these ranges are indicative, not absolute.

Limitations and food safety considerations

MAP does not sterilise

MAP reduces the rate of microbial growth but does not inactivate microorganisms. Products remain perishable and require unbroken cold chain throughout distribution, retail, and consumer storage. A package that is opened, resealed, or stored at elevated temperature loses its protective atmosphere rapidly.

Anaerobic conditions and pathogens

Excluding oxygen suppresses aerobic spoilage organisms — which normally produce visible or olfactory signs of spoilage — while potentially allowing anaerobic and facultative anaerobic pathogens to survive without producing obvious signs of deterioration. Of particular concern:

• Clostridium botulinum: capable of growth and toxin production under anaerobic conditions at temperatures above 3°C (non-proteolytic type B, E, F) or 10°C (proteolytic type A, B). MAP fish and ready meals in the temperature range 3–8°C represent a potential risk if temperature control is inadequate.
• Listeria monocytogenes: psychrotrophic, capable of growth at refrigerator temperatures (1–4°C), facultative anaerobe. MAP does not reliably inhibit Listeria at refrigerator temperatures.

For this reason, MAP is almost always used in combination with refrigeration and often with other hurdles such as mild acidification, reduced water activity, or post-packaging heat treatment. The combination of MAP with pH control (acid foods, pH < 4.6) significantly reduces botulism risk.

Colour misinterpretation (red meat)

High-O₂ MAP of red meat creates a bright red surface colour that consumers associate with freshness. However, once the package is opened, the interior of the meat (which was never exposed to high O₂) may appear brown (metmyoglobin) — a normal biochemical response to low oxygen in the pack interior, not an indicator of spoilage. This can cause consumer confusion and food waste.

CO₂-induced package collapse

As CO₂ dissolves into the food product during chilled storage, headspace volume decreases and flexible packs may appear vacuum-packed or deflated. Consumers sometimes interpret collapsed packaging as a sign of spoilage or tampering. Sufficient nitrogen in the gas blend mitigates this.

Relation to other preservation methods

MAP is rarely the sole preservation method; it is most effective when combined with:

• Refrigeration: mandatory for MAP fresh products; temperature is the primary control for microbial growth rate
• High pressure processing (HPP): post-packaging HPP is sometimes applied to MAP products to achieve pasteurisation-equivalent microbial reduction without heat; the combination extends shelf life further while preserving fresh quality
• Vacuum skin packaging (VSP): a related technique in which film is drawn tightly over the product surface under vacuum, without gas substitution; maintains product form and extends shelf life for premium red meat
• Active packaging: incorporation of O₂ scavengers, CO₂ emitters, or ethylene absorbers within the packaging material to actively maintain the target atmosphere throughout distribution

MAP is one of several overlapping preservation technologies described under hurdle technology — the principle that multiple moderate preservation hurdles in combination achieve safety and shelf life targets that no single method can reach alone.

Regulatory framework

In the European Union, gases used in MAP are classified as food additives under Regulation (EC) No 1333/2008. Oxygen (E 948), carbon dioxide (E 290), and nitrogen (E 941) are approved for use in food packaging without specific dose limits (quantum satis). Gas mixtures must be food-grade; specifications are defined in Commission Regulation (EU) No 231/2012.

In the United States, MAP gases used in direct food contact packaging are regulated by the FDA under GRAS (Generally Recognised As Safe) status. Modified atmosphere packaging for specific high-risk categories — particularly seafood and ready-to-eat products — falls within HACCP requirements under FDA regulations (21 CFR Part 123 for fish; 21 CFR Part 120 for juice). The USDA regulates MAP of meat and poultry products.

Labelling requirements in both jurisdictions generally do not require disclosure of MAP on-pack unless the specific gas composition is considered material to the consumer (for example, CO₂ in carbonated beverages is declared). In the EU, packed-in-protective-atmosphere labelling is required for many MAP products under Regulation (EU) No 1169/2011 (Food Information to Consumers).

Advantages and limitations

Advantages

• Extends refrigerated shelf life without heat, pressure, or chemical additives
• Preserves fresh sensory characteristics (colour, texture, flavour, aroma)
• Compatible with a wide range of food categories (meat, fish, produce, dairy, bakery, ready meals)
• Enables longer distribution chains and reduced food waste in the supply chain
• Can be combined with other preservation hurdles for enhanced efficacy
• Permeable film MAP (EMA) is tailored to respiring fresh produce without causing anaerobiosis

Limitations

• Does not inactivate microorganisms; cold chain is mandatory throughout
• Anaerobic conditions may allow growth of C. botulinum and L. monocytogenes without organoleptic warning signs
• Package integrity is critical; any seal failure invalidates the modified atmosphere
• CO₂ dissolution causes apparent pack collapse that may confuse consumers
• High-O₂ MAP accelerates lipid oxidation despite maintaining red colour
• Requires investment in gas supply infrastructure, specialised packaging equipment, and high-barrier films
• Gas composition must be optimised individually for each product; incorrect formulation can accelerate spoilage or cause tissue damage in produce