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Achieving 100% MAP quality checks

18 December 2017

An in-line quality control system, which can check the oxygen content and seal integrity of every single MAP that leaves the thermoformer form, fill and seal packaging machine, was the subject of a presentation at the PPMA show Learning Hub.

Modified Atmosphere Packaging (MAP) is designed to extend the shelf life of perishable food and preserves its visual appearance. The majority of retail fresh food is now packaged in this way, with the air in the package being replaced with a gas mixture suited to the particular food.

Meat begins to deteriorate immediately after slaughter due to microbiological organisms and biochemical reactions. It is difficult this spoiling process as the organisms responsible are already present in the product. The best way to preserve freshness is to remove air from the package and replace it with gases that slow down the process of deterioration. By removing oxygen through MAP, meat product quality is retained for up to 21 days, as compared to seven days with older preservation methods.

Ideally, oxygen should be totally eliminated from MAP but due to physical principles, a small percentage of oxygen will remain in the package. To minimise the growth of aerobic micro-organisms, the oxygen content in a package should be as low as possible to prevent early spoilage of food. It is therefore critical to ensure the residual oxygen content is acceptably low. To do this, MAP packaging machines evacuate the air and flush the packaging chamber using different gases, and then seal the product in. As well as nitrogen and oxygen, inert gases such as argon or helium are also used for flushing.

Although MAP is a well-established process, stringent quality control is vital. There are a number of factors that can influence the quality of MAP, and therefore increase the risk that a packaged food product will not meet its shelf life specifications. These include incorrect gas levels and empty gas cylinders as well as faults in the gas flushing or sealing processes. If the MAP gases escape, the oxygen content rises. This means not only will the appearance and taste of the food deteriorate faster than expected, but it may also present a health hazard.

Since a small percentage of oxygen remains in a MAP, measuring the concentration inside the package is the preferred method for confirming the quality. Current quality control techniques used to do this will only test random sample packages taken from the line. The residual oxygen content in the packages of one index is manually analysed using an invasive oxygen sensor system (sensor needle). During the analysis, the film is damaged, and neither package nor contents are returned to the line, which adds to waste. If a leaking package or incorrect gas composition is detected, the line has to be stopped and all packages preceding the defective one may have to be rejected.

The GEA OxyCheck overcomes the shortcomings of sample MAP quality control techniques, providing a 100% product quality control inspection. It is also non-invasive, which means that the film or the seal are not damaged and the contents are not wasted. OxyCheck incorporates a measurement station with optical sensors above each packaging lane that inspect every package immediately after sealing. Optical sensors in a second measurement station then re-check the oxygen content a short while later to identify leakage by detecting an increase in the oxygen concentration.

A vital component of OxyCheck is the sensor spot which is printed on the inner (product-facing) side of the lidding film. The measurement technique uses the fluorescence properties of a dye in the spot. As this dye absorbs light, it emits specific wavelengths of light. The fluorescence of this dye changes according to the amount of oxygen present, and the change is detectable which makes it possible to accurately measure oxygen concentration from outside the package.

The optical sensors shine light on the sensor spot and measure the wavelength of the light that fluoresces from the dye. As temperature also influences the dye’s fluorescence, the sensors incorporate non-contact thermometers to adjust for temperature in the calculation. Packages that don’t meet the specifications are automatically rejected and do not enter the supply chain.

A food safe process
The food-safe dye is mixed in a polystyrene based liquid, and printed on the inner side of the lidding film. It conforms to all relevant EU regulations for plastic material having food contact. The sensors use pulsed light from an LED, which is safe for food as well as machine operators.

There are several possibilities for printing the sensor spot. The film manufacturer can be licensed to pre-print the spot on the film or a printer station can be added to a GEA thermoformer to print the sensor spot in-line. The OxyCheck technology opens the door to more future possibilities than monitoring the MAP conditions and seal quality at the food manufacturer. GEA has, for example, already conducted tests to integrate the technology into a hand-held scanning device which will allow post-production control at distribution centers, on the supermarket floor or even at home.

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