How to Create Modified Atmosphere Conditions for Food Storage

Every time you pick up a bag of pre-washed salad or a tray of fresh chicken from the supermarket, there’s a good chance the air inside that package isn’t regular air at all. It has been carefully modified – either by the produce itself or by machines – to slow down spoilage and keep your food fresh longer. This technology is called Modified Atmosphere (MA) packaging, and it works by adjusting the levels of oxygen, carbon dioxide, and nitrogen inside a sealed package. The two core methods to achieve this are passive MA and active MA, and both rely on a smart selection of packaging films and coatings to regulate gas exchange.

What exactly is a modified atmosphere? 🔗

Normal air contains roughly 78% nitrogen, 21% oxygen, and a tiny fraction of carbon dioxide. This mix is far from ideal for preserving perishable food. Oxygen accelerates spoilage by promoting lipid oxidation, enzymatic browning, and the growth of aerobic microorganisms. Modified atmosphere packaging addresses this by changing the gas composition inside the package – typically lowering oxygen, raising carbon dioxide, and using nitrogen as a filler – to create an environment where food deteriorates much more slowly.

The gas mixture chosen depends on the type of food. For fruits and vegetables, oxygen is usually kept between 3-5% to slow down respiration without causing tissue damage. For red meat, oxygen may actually be raised to around 80% to maintain a bright red colour. Carbon dioxide above 10% can be toxic to plant tissues, so it is carefully controlled in produce packaging. Nitrogen, being inert, primarily serves to prevent the package from collapsing under vacuum-like conditions.

Passive modified atmosphere: letting nature do the work 🔗

Passive MA is the simpler of the two approaches. It relies entirely on the natural respiration of the produce sealed inside the package. When you place fresh fruits or vegetables in a sealed film bag, they continue to respire – consuming oxygen and releasing carbon dioxide. Over time, this biological process gradually shifts the internal atmosphere toward lower O₂ and higher CO₂ levels.

The key to making passive MA work is choosing a packaging film whose gas permeability matches the respiration rate of the specific product. The film must allow oxygen to enter at a rate that offsets the produce’s oxygen consumption, and it must vent carbon dioxide at a rate that prevents toxic build-up. When these two processes reach a balance, an equilibrium atmosphere is established inside the package – and this is the point where shelf life is maximised.

Passive MA is commonly used for fresh-cut salads, leafy greens, whole fruits, and herbs. Its main advantage is simplicity: no specialised gas-flushing equipment is needed. However, it has a significant drawback – reaching the desired equilibrium takes time. During this lag period, the food may be exposed to suboptimal conditions, which can slightly reduce the effectiveness compared to active methods.

Active modified atmosphere: immediate control 🔗

Active MA takes a more hands-on approach. Instead of waiting for produce to naturally alter its own atmosphere, active methods immediately replace the air inside the package with a pre-determined gas mixture. This is done at the point of packaging, so optimal conditions are established from the start.

Gas flushing 🔗

Gas flushing is the most widely used active MA technique. During the packaging process, the air inside the package is displaced by injecting a controlled mixture of nitrogen, carbon dioxide, and sometimes a small amount of oxygen. This rapidly brings the headspace to the target gas composition. Gas flushing is especially popular for products like snack foods, dried fruits, nuts, shredded cheese, and processed meats that need immediate oxygen removal to prevent rancidity.

Vacuum packaging 🔗

Vacuum packaging is another active method. Here, the air is physically drawn out of the package before it is sealed, creating a near-total vacuum. This dramatically reduces the oxygen available for oxidation and microbial growth. Vacuum packaging is the method of choice for fresh and processed meats, hard cheeses, and cured products. The flexible packaging film conforms tightly to the product’s shape, minimising headspace.

Compensated vacuum 🔗

A third approach combines both techniques: the package is first evacuated and then flushed with the desired gas mixture before sealing. This compensated vacuum method ensures that residual oxygen levels are extremely low, making it ideal for highly oxygen-sensitive products.

Snorkel-type machines 🔗

For bulk and large-scale operations, snorkel machines offer another active MA solution. A nozzle (the “snorkel”) is inserted into the package after filling, pulls a vacuum, and then injects the modified atmosphere before the package is sealed. This method is particularly useful for large bags or bulk packs of meat, seafood, and shredded vegetables.

The role of gases in modified atmosphere packaging 🔗

Three gases form the foundation of almost every MA system, each performing a specific function.

Oxygen (O₂) is the most critical gas to control. In most products, it is reduced to slow spoilage. However, for red meat, a high oxygen level (~80%) is maintained to keep the myoglobin pigment in its bright red, oxygenated form. For fresh produce, O₂ is typically kept at 3-5%.

Carbon dioxide (CO₂) is the main antimicrobial gas. It penetrates bacterial cell membranes and lowers intracellular pH, effectively increasing the lag phase and generation time of spoilage organisms. It is particularly effective against Gram-negative bacteria like Pseudomonas species, which are among the most common food spoilers. However, CO₂ must be carefully dosed – above 10% it becomes phytotoxic to most fruits and vegetables.

Nitrogen (N₂) is chemically inert and serves primarily as a filler gas. It prevents package collapse that would otherwise occur if CO₂ were the only replacement gas (since CO₂ is readily absorbed by food and moisture). Nitrogen also displaces oxygen in products like chips and nuts, protecting them from oxidative rancidity.

Packaging films: the gatekeepers of gas exchange 🔗

Whether using passive or active MA, the success of the system depends heavily on the packaging film selected. The film acts as a semi-permeable barrier that controls how fast gases move in and out of the package. Two critical properties govern this: oxygen transmission rate (OTR) and carbon dioxide transmission rate (CO₂TR).

Common film materials 🔗

Several polymeric films are widely used in MA packaging, each offering a different balance of gas permeability, strength, clarity, and cost.

Low-density polyethylene (LDPE) is one of the most common choices for fresh produce packaging. It is soft, flexible, easy to heat-seal, and relatively transparent. LDPE has good moisture barrier properties but relatively high gas permeability, making it suitable for produce with moderate to high respiration rates.

High-density polyethylene (HDPE) has a denser molecular structure than LDPE, which gives it lower gas permeability. This makes it better suited for products that require a tighter oxygen barrier, though it is less flexible.

Polypropylene (PP), including its biaxially oriented form (BOPP), offers good clarity and strength with moderate gas barrier properties. It is often used for produce that needs a lower respiration rate environment.

Polyvinyl chloride (PVC) is a common stretch wrap material used for overwrapping trays of meat, fruits, and vegetables. It provides moderate gas permeability and good cling properties.

Polyvinylidene chloride (PVDC) offers excellent barrier properties against oxygen, water vapour, odours, and flavours. It is often used as a coating layer in multi-layer films for high-barrier applications.

Ethylene vinyl alcohol (EVOH) is one of the best oxygen barrier polymers available and is frequently used in multi-layer structures for oxygen-sensitive products like processed meat and ready meals. However, its barrier properties decrease at high humidity, so it is typically sandwiched between moisture-resistant layers.

Polyethylene terephthalate (PET) provides a moderate oxygen barrier along with good mechanical strength and clarity, making it popular for rigid and semi-rigid MA containers.

How film selection works in practice 🔗

For most fresh produce, the ideal film must be significantly more permeable to CO₂ than to O₂. This is because CO₂ can build up quickly from respiration and needs to escape before reaching phytotoxic levels. The ratio of CO₂ to O₂ permeability (sometimes called the selectivity ratio) is a key factor. Films with a high selectivity ratio allow CO₂ to exit relatively easily while keeping oxygen entry controlled.

Film thickness also plays a role – thinner films have higher gas transmission rates. Temperature affects permeability too; as storage temperature rises, gas transmission rates through the film increase, which is why maintaining a consistent cold chain is critical for MA-packaged products.

Oxygen scavengers and other active packaging components 🔗

Beyond films and gas flushing, several active packaging components can be placed inside the package to fine-tune the atmosphere.

Oxygen scavengers are small sachets – usually containing iron powder – that chemically react with and remove residual oxygen from the headspace. They can bring oxygen levels down to parts-per-million levels, far lower than what gas flushing alone can achieve. These are commonly found in packages of bread, dried snacks, and processed meat.

Carbon dioxide scavengers/absorbers prevent CO₂ from accumulating to harmful levels, which is particularly useful for highly respiring produce. Conversely, CO₂ emitters can release carbon dioxide into the package to boost antimicrobial activity.

Ethylene scavengers are especially important for climacteric fruits like bananas, apples, and tomatoes. Ethylene is a natural ripening hormone, and removing it from the package atmosphere helps delay ripening and extend shelf life.

Moisture absorbers (desiccants) help control humidity inside the package. Excess moisture promotes microbial growth, while too little causes wilting and weight loss in fresh produce.

Edible coatings as a modified atmosphere strategy 🔗

An increasingly popular alternative – or complement – to traditional film-based MA packaging is the use of edible coatings. These are thin layers of natural materials applied directly to the surface of fruits and vegetables. They create a semi-permeable barrier on each individual product, effectively generating a modified atmosphere at the surface level.

Types of edible coatings 🔗

Edible coatings fall into three broad categories:

Polysaccharide-based coatings use materials like chitosan, starch, cellulose, alginate, or pectin. Chitosan is particularly popular because of its natural antimicrobial properties, good film-forming ability, and biodegradability. Chitosan coatings reduce moisture loss, regulate gas exchange, and inhibit microbial growth.

Lipid-based coatings include waxes such as carnauba wax, beeswax, and candelilla wax. Wax coatings create a barrier that raises CO₂ and lowers O₂ around the fruit, effectively suppressing respiration, reducing water loss, and slowing metabolic activity. Waxing of citrus fruits and apples is a long-standing commercial practice.

Protein-based coatings use materials like whey protein, soy protein, zein (from corn), or gelatin. These coatings generally provide a strong oxygen barrier, making them useful for oxidation-sensitive products.

Modern formulations often combine materials from multiple categories – for example, a chitosan-beeswax composite – to achieve better moisture resistance, gas regulation, and antimicrobial protection simultaneously.

How coatings differ from film packaging 🔗

The main difference is that edible coatings modify the atmosphere around each individual fruit or vegetable, whereas film packaging modifies the atmosphere in the collective headspace. This means coatings can provide more uniform protection, even when individual items are separated from the original package. However, coating thickness and uniformity are harder to control at scale compared to standardised film packaging.

Choosing between passive and active MA 🔗

The decision between passive and active MA depends on several factors: the product’s respiration rate, the target shelf life, the supply chain length, and the available equipment.

Passive MA works well for fresh produce with moderate respiration rates and shorter supply chains. It is simpler and cheaper since it requires no gas-flushing equipment. Products like bagged salads, spinach, and fresh herbs are commonly packaged this way.

Active MA is preferred when the product needs immediate protection – for example, meat, seafood, ready meals, and high-value produce with long distribution channels. The upfront investment in gas-flushing or vacuum-packaging equipment pays off through significantly longer shelf life and reduced waste.

In many commercial operations, the two approaches are combined. For instance, a package of fresh-cut vegetables might be gas-flushed to quickly establish a low-oxygen atmosphere (active), and then the ongoing respiration of the produce fine-tunes the atmosphere during storage (passive).

Food safety considerations 🔗

While MA packaging effectively slows the growth of aerobic spoilage organisms, it does not eliminate all risks. In fact, by suppressing spoilage bacteria, MA can allow pathogenic anaerobic or facultatively anaerobic organisms – such as Clostridium botulinum, Listeria monocytogenes, and Salmonella – to grow without the usual visible or olfactory signs of spoilage. The food may look and smell fine while harbouring dangerous pathogens.

This is why MA packaging must always be combined with proper temperature control (maintaining the cold chain below 3-5°C), and in some cases additional hurdles like low pH, reduced water activity, or preservatives. Integrating HACCP (Hazard Analysis and Critical Control Points) protocols into MA packaging operations is essential for ensuring both quality and safety.

Real-world applications at a glance 🔗

MA packaging is used across a wide range of food products. Fresh-cut salads and prepared fruit rely on passive MA with carefully selected permeable films. Fresh red meat uses high-oxygen active MA to maintain colour. Poultry, pork, and cooked meats use high CO₂ mixtures. Bakery products like bread and cakes use CO₂-rich atmospheres to inhibit mould growth. Cheese, nuts, and snack foods use nitrogen flushing to prevent oxidative rancidity. Seafood combines low O₂ and elevated CO₂ to delay bacterial spoilage.

The global MAP market continues to grow as consumer demand for fresh, minimally processed, preservative-free food increases. Advances in biodegradable films, smart packaging with freshness indicators, and nano-enhanced edible coatings are pushing the technology forward.

What do you think? Have you ever compared the shelf life of a MAP-sealed bag of salad with an unsealed one at home? And as packaging technology moves toward biodegradable and edible materials, how do you think this will change the way we buy and store fresh food in the future?

References

1. https://en.wikipedia.org/wiki/Modified_atmosphere
2. https://pmc.ncbi.nlm.nih.gov/articles/PMC7089433/
3. https://www.nexair.com/learning-center/active-vs-passive-modified-atmosphere-packaging/
4. https://pmc.ncbi.nlm.nih.gov/articles/PMC4554610/
5. https://www.sciencedirect.com/topics/engineering/oxygen-barrier
6. https://pmc.ncbi.nlm.nih.gov/articles/PMC10486622/
7. https://pmc.ncbi.nlm.nih.gov/articles/PMC9864592/
8. https://pmc.ncbi.nlm.nih.gov/articles/PMC8695420/
9. https://www.sciencedirect.com/science/article/abs/pii/S1359511325001771