Modified Atmosphere Packaging (MAP) Explained | The Science

Fresh fruit, vegetables, and flowers don’t stop living the moment they’re harvested. They keep breathing — consuming oxygen, releasing carbon dioxide, and burning through their own stored sugars — right up until the point they’re eaten or discarded. Modified Atmosphere Packaging (MAP) works by managing that ongoing respiration, slowing it down just enough to extend marketable life without stressing the produce into early decline. Postharvest losses from inadequate storage technology are estimated at 25–40% of harvested fruit and vegetables globally (Modified Atmosphere Packaging of Fruits and Vegetables for Extending Shelf-Life: A Review). Understanding how MAP actually works — beyond “the bag keeps things fresh” — is the difference between a packaging decision backed by decades of postharvest physiology research and one that’s just a plastic liner.

Respiration: The Process MAP Is Designed to Slow

Every piece of harvested produce continues respiring — taking in oxygen (O₂) and converting stored sugars into energy, releasing carbon dioxide (CO₂) and water as by-products. This is a normal, unavoidable part of staying alive after harvest, and it’s the process controlled atmosphere and MAP storage are both built around managing (UC Davis Postharvest Research and Extension Center, Controlled Atmosphere and MAP overview). The problem is that respiration also drives ageing: the faster a crop respires, the faster it uses up its reserves, softens, loses flavour, and eventually spoils.

Lowering O₂ and raising CO₂ around produce slows its respiration and metabolic rate, which is the primary mechanism behind why MAP and controlled atmosphere storage extend shelf life (Kitinoja & Kader, cited in Controlled Atmosphere Storage overview). Research from the Produce Marketing Association’s MAP White Paper, drawing on foundational work by postharvest scientist Adel Kader, found that high CO₂ and low O₂ used together can in some cases reduce respiration more than either gas would alone (Kader, Zagory & Kerbel, 1988). The same research notes CO₂ above roughly 10% has been shown to suppress a range of decay-causing fungi and bacteria — but also that individual crops differ significantly in how much CO₂ they can tolerate before the gas itself starts damaging plant tissue.

Not One Atmosphere Fits All Crops

UC Davis’s Postharvest Research and Extension Center — built on decades of produce-specific research led by the late Dr. Adel Kader — publishes crop-by-crop guidance precisely because “the right atmosphere” is a different answer for every crop. For oranges, the Center’s produce fact sheet recommends 5–10% O₂ combined with 0–5% CO₂ to delay senescence and retain firmness, while noting this combination has little effect on decay, meaning fungicide treatment and temperature management remain the dominant tools for decay control in citrus specifically (UC Davis PREC, Orange produce facts sheet). Fungistatic CO₂ levels of 10–15% are deliberately avoided in oranges because of other tolerance issues the fruit shows at that concentration.

Cherries are a useful contrast: UC Davis’s cherry fact sheet notes that ethylene does not accelerate cherry ripening and that cherries show minimal response to ethylene exposure — which is why the Center’s cherry guidance focuses almost entirely on CO₂-driven decay suppression and high humidity for stem colour retention, rather than ethylene management (UC Davis PREC, Cherry produce facts sheet). The same fact sheet confirms that CA and MAP both work in cherries by reducing respiration rate to extend postharvest life, with elevated CO₂ specifically credited for suppressing decay development.

Kiwifruit research published in the New Zealand Journal of Crop and Horticultural Science measured the actual atmospheres MAP created in commercial trials: 12–15% O₂ combined with 3–4% CO₂ at 1°C storage, shifting to 12–16% O₂ and 7–10% CO₂ when fruit moved to 20°C simulated retail conditions. That trial found MAP reduced kiwifruit softening during cool storage, and — notably — that this quality benefit was preserved into the subsequent retail shelf-life period even after the fruit left MAP conditions (Benefits of modified atmosphere packaging in maintaining ‘Hayward’ kiwifruit quality at room temperature retail conditions, 2022).

Strawberries offer a fourth data point on how fine-grained this crop-specificity gets: research published in the International Journal of Food Science & Technology identified an optimal equilibrium of 10% O₂ and 10% CO₂ for strawberries, achievable with a microporous film using four 100-micron perforations. At that specific equilibrium, strawberries showed total phenolic content roughly 25% higher, anthocyanin content around 13% higher, and flavonoid content around 29% higher than unpackaged controls — meaning the right atmosphere didn’t just extend shelf life, it measurably improved the fruit’s nutritional profile relative to unprotected storage.

Equilibrium Modified Atmosphere: Why the Bag Isn’t Sealed Solid

A common misconception is that a MAP bag works by cutting produce off from air entirely. In practice, the opposite is closer to true. Passive MAP relies on the produce sealed inside a low-barrier film establishing its own atmosphere over time, through its own respiration, rather than through any active gas control after sealing (registered microperforated films patent literature, USPTO). If a bag were completely impermeable, oxygen inside would keep dropping and CO₂ would keep climbing until the crop suffocated — a condition that causes off-flavours, fermentation, and rapid tissue breakdown.

Instead, MAP bags are engineered with a specific gas permeability — through the film’s polymer composition and, in many designs, precisely sized micro-perforations — that lets a controlled amount of O₂ in and CO₂ out. Over the first hours to days of storage, the atmosphere inside the bag settles into what’s known as equilibrium modified atmosphere (EMA): a stable balance point where the rate of gas exchange through the film matches the crop’s own respiration rate. This equilibrium point can be predicted mathematically, using models that account for produce respiration and transpiration rates, packaging surface area, film permeability, and storage temperature, rather than discovered only through trial and error on real fruit (Modified Atmosphere Packaging: Design and Optimization Strategies for Fresh Produce, IntechOpen).

Why MAP Bags Are Engineered Per Crop, Not One-Size-Fits-All

Every crop respires at a different rate, and that rate itself changes with temperature, maturity, and time in storage. This is why properly designed MAP bags are specified using three key film properties:

OTR (Oxygen Transmission Rate) — how much oxygen passes through the film over time, matched to how much oxygen the crop consumes
CTR (Carbon Dioxide Transmission Rate) — how much CO₂ escapes the bag, preventing the atmosphere from becoming too extreme for the crop to tolerate
WVTR (Water Vapour Transmission Rate) — how much moisture passes through the film, which determines whether the bag maintains high humidity around the crop without allowing condensation to pool

Common polyolefin films used in produce packaging have a CO₂-to-O₂ permeability ratio of roughly 3 to 7, meaning CO₂ naturally passes through several times faster than O₂ (Modified Atmosphere Packaging — an overview, ScienceDirect Topics). For crops whose ideal atmosphere calls for both very low O₂ and only moderately low CO₂, that ratio works well. For crops needing a different balance, standard films can make it physically difficult to hit the target atmosphere at all — which is part of why the Produce Marketing Association’s own industry MAP guidance stresses understanding each specific polymer’s individual gas transmission properties, rather than treating film selection as interchangeable across crops.

Humidity Control: The Other Half of the Equation

Gas modification is only one part of what a well-designed MAP bag does. WVTR also governs humidity, and for most fresh produce, humidity management matters just as much as oxygen and CO₂ control. UC Davis’s cherry fact sheet specifically flags high humidity as important for maintaining stem colour and overall fruit quality, independent of the gas-modification benefit. Most crops need to be held around 90–95% relative humidity to prevent water loss, wilting, and shrivelling — but high humidity in an unmanaged environment also creates the conditions for condensation, which is one of the fastest routes to fungal rot in cold storage.

A correctly specified MAP bag threads this needle: it holds humidity high enough to protect the crop from moisture loss, while its WVTR allows enough vapour exchange to prevent free water from forming and pooling.

Ethylene: A Crop-by-Crop Complication MAP Alone Doesn’t Always Solve

Slowing respiration also tends to reduce the rate at which many crops produce ethylene, the plant hormone responsible for triggering and accelerating ripening and senescence. But ethylene’s relevance varies enormously by crop — UC Davis’s cherry fact sheet is explicit that cherries respond minimally to ethylene and that it does not accelerate their ripening, meaning ethylene management is largely irrelevant to cherry postharvest strategy. Kiwifruit sits at the opposite end: research trials specifically tested MAP with an added ethylene scrubber against MAP alone, because kiwifruit’s known sensitivity to ethylene meant gas modification by itself wasn’t assumed to be sufficient protection (Benefits of modified atmosphere packaging in maintaining ‘Hayward’ kiwifruit quality, 2022).

For ethylene-sensitive crops, MAP alone doesn’t remove ethylene that’s already present in a sealed bag. It continues to drive ripening even after the crop is back in cold storage, which is why MAP bags for ethylene-sensitive produce are frequently paired with a dedicated ethylene absorber — handling what gas modification alone cannot.

The Practical Case for Sea Freight

The commercial upside of getting MAP right is straightforward: it turns marginal transit windows into workable ones. Muscadine grape research found that grapes tolerant of high CO₂ could be held in controlled atmosphere for up to 42 days at 4°C with better quality and reduced decay compared to air storage, and separately that a 5% O₂ plus 15% CO₂ atmosphere supported 6 weeks of storage at 1.1–2.2°C (Evaluation of modified atmosphere packaging system developed through breathable technology to extend postharvest life of fresh muscadine berries, 2024). Trial data across other crops — blueberries, iceberg and cos lettuce, citrus — has similarly shown MAP-protected produce reaching 5+ weeks of cold storage in genuinely marketable condition, against unprotected controls failing well before that point.

The Practical Takeaway

MAP works because it targets the actual biological process driving spoilage — respiration — rather than simply creating a barrier between produce and the outside world. But the research is consistent on one point above all others: there is no universal MAP recipe. Oranges, cherries, kiwifruit, strawberries, and grapes each call for a measurably different atmosphere, tolerate different CO₂ ceilings, and respond differently — or not at all — to ethylene. Crop-specific engineering, backed by the kind of produce-by-produce research UC Davis PREC and similar institutions have built over decades, is what actually determines whether a MAP bag extends shelf life or works against the crop it’s meant to protect.

View the Biopac 2026 Product Catalogue (PDF)

See the science in real trials

References

UC Davis Postharvest Research and Extension Center — Cherry produce facts sheet (Adel A. Kader).
UC Davis Postharvest Research and Extension Center — Orange produce facts sheet.
UC Davis Postharvest Research and Extension Center — Modified Atmosphere Packaging of Fresh Produce (Zagory & Kader).
Kader, A.A., Zagory, D., & Kerbel, E.L. (1988) — cited in Modified Atmosphere Packaging (MAP) White Paper, Produce Marketing Association.
Benefits of modified atmosphere packaging in maintaining ‘Hayward’ kiwifruit quality at room temperature retail conditions, New Zealand Journal of Crop and Horticultural Science, 2022.
Equilibrium modified atmosphere packaging on strawberry postharvest quality, International Journal of Food Science & Technology.
Evaluation of modified atmosphere packaging system developed through breathable technology to extend postharvest life of fresh muscadine berries, 2024.
Modified Atmosphere Packaging: Design and Optimization Strategies for Fresh Produce, IntechOpen.
Modified Atmosphere Packaging — an overview, ScienceDirect Topics.
Modified Atmosphere Packaging of Fruits and Vegetables for Extending Shelf-Life: A Review.