Can a MAP Packaging Tray be used in high-pressure processing (HPP) or heat-sealing environments?

The MAP Packaging Tray can be used in both high-pressure processing (HPP) and heat-sealing environments, but only when the tray is specifically engineered for those conditions. Not all MAP Packaging Trays are created equal: material selection, barrier layer construction, wall thickness, and seal geometry all determine whether a tray will perform reliably under elevated pressure or thermal stress. Using the wrong tray in either environment risks seal failure, delamination, tray deformation, and — most critically — loss of the modified atmosphere that gives MAP packaging its shelf-life advantage.

What Is HPP and Why Does It Challenge a MAP Packaging Tray?

High-pressure processing (HPP) is a cold pasteurization technique that subjects sealed food products to pressures typically ranging from 400 to 600 MPa (58,000–87,000 psi) for 3 to 6 minutes. Because water is nearly incompressible, the pressure is transmitted uniformly through the product and packaging, inactivating pathogens such as Listeria, Salmonella, and E. coli without the use of heat.

The challenge for any MAP Packaging Tray is that the headspace gas inside the tray is highly compressible. At 600 MPa, that gas volume compresses dramatically — sometimes by more than 15% — and then re-expands when pressure is released. This compression-expansion cycle exerts severe mechanical stress on the tray walls and the sealed lidding film. A tray not rated for HPP will buckle, crack at stress points, or experience seal peeling, which immediately compromises the modified atmosphere.

Material Requirements for an HPP-Compatible MAP Packaging Tray

For a MAP Packaging Tray to survive HPP cycles, its material stack must be flexible enough to absorb compression forces without cracking or delaminating. The following materials are commonly validated for HPP use:

• Polypropylene (PP): Widely used due to its flexibility, chemical resistance, and ability to recover shape after compression.
• EVOH barrier layers: Provide the oxygen transmission rate (OTR) performance needed for MAP, and remain stable under HPP pressures when sandwiched correctly within a PP or PE laminate.
• Polyethylene (PE) laminates: Offer good elongation properties that help the tray flex during pressurization without permanent deformation.
• Avoid rigid PET or CPET: These materials have low elongation at break and are prone to cracking under HPP compression cycles.

The lidding film bonded to the MAP Packaging Tray is equally critical. It must maintain a hermetic seal through both the compression and decompression phases. Peel-strength values of at least 8–12 N/15mm are typically required for HPP-rated lidding films, and the film itself should have an elongation at break exceeding 300%.

Heat-Sealing Compatibility: Temperature, Dwell Time, and Tray Geometry

Heat-sealing is the standard method of closing a MAP Packaging Tray on tray-sealing or thermoforming machines. The process uses a heated sealing tool pressed against the flange of the tray to bond the lidding film. The key parameters are sealing temperature, dwell time, and sealing pressure — and all three must be matched to both the tray material and the lidding film.

Typical Heat-Sealing Parameters by Tray Material

Exceeding the upper sealing temperature for any given MAP Packaging Tray material risks warping the tray flange, which creates micro-gaps in the seal and allows atmospheric oxygen to infiltrate the modified atmosphere. Conversely, sealing at too low a temperature produces a weak, peelable bond that fails during distribution. Seal integrity testing — either by dye penetration, vacuum decay, or CO₂ sensor measurement — should be performed at the start of every production run.

Can the Same MAP Packaging Tray Be Used for Both HPP and Heat-Sealing?

This is a common question from producers who want to heat-seal a MAP Packaging Tray on their existing tray sealer and then pass the sealed units through an HPP vessel. The answer is yes — this is actually the standard workflow for HPP-treated MAP products such as fresh-cut guacamole, sliced deli meats, and ready-to-eat seafood. The process sequence is:

1. Fill the MAP Packaging Tray with product.
2. Flush with the target gas blend (e.g., 70% CO₂ / 30% N₂ for cooked meats).
3. Heat-seal the lidding film onto the tray flange.
4. Place sealed trays into HPP vessel carriers (water is the pressure-transmitting medium).
5. Process at target pressure (typically 500–600 MPa) for the validated dwell time.
6. Remove trays, inspect seals, and transfer to cold-chain distribution.

The critical caveat is that the MAP Packaging Tray and its lidding film must both be individually validated for HPP — not just one or the other. A tray supplier should be able to provide HPP validation data, including post-process OTR measurements and seal integrity results across multiple pressure cycles.

Impact of HPP on the Modified Atmosphere Inside the Tray

One aspect users frequently overlook is that HPP itself alters the gas composition inside a MAP Packaging Tray. Because CO₂ is more soluble in water and food matrices than O₂ or N₂, a portion of the CO₂ in the headspace dissolves into the product during pressurization. After HPP, the residual CO₂ level in the headspace may drop by 10–30% depending on product water activity and the initial gas ratio.

To compensate, producers typically over-flush with CO₂ prior to sealing — for example, targeting an initial headspace of 80% CO₂ when the desired post-HPP level is 60%. Consulting your HPP equipment supplier and gas supplier together is essential to dial in the correct pre-seal gas composition for your specific MAP Packaging Tray format and product type.

Key Checklist Before Using a MAP Packaging Tray in HPP or Heat-Sealing Applications

Before committing a MAP Packaging Tray format to either processing environment, verify the following with your tray and film suppliers:

• HPP pressure rating: Confirm the tray and lid system is validated to at least 600 MPa if you intend to run at maximum HPP pressures.
• Post-HPP OTR retention: Request OTR data measured after 3–5 HPP cycles, not just from virgin material.
• Flange flatness tolerance: A MAP Packaging Tray flange must be flat to within ±0.1 mm to achieve a consistent heat seal — warped flanges from poor tooling or incorrect storage will cause seal failures.
• Food-contact compliance: Ensure the tray carries FDA (21 CFR) or EU Regulation 10/2011 compliance documentation for all material layers, including any tie layers or adhesives.
• Cold-chain compatibility: If the MAP Packaging Tray will be stored at 0–4°C post-HPP, verify that the barrier layers retain their OTR performance at refrigeration temperatures, as EVOH performance can degrade at high humidity.
• Sealing machine compatibility: Confirm the tray dimensions and flange width are compatible with your tray sealer tooling to avoid uneven heat distribution during sealing.