By Eamonn Ryan
Building on her introduction to Modified Atmosphere Packaging (MAP), Perm Mthethwa of the Agricultural Research Council’s Natural Resources and Engineering unit went on to demystify how a MAP system actually works. Her presentation, delivered to a cold chain audience, highlighted that MAP is not a single machine but a co-ordinated system of gas supply, mixing, control and packaging.
© Cold Link Africa
At the heart of MAP are three key gases: oxygen, carbon dioxide and nitrogen. These gases are sourced from cylinders or centralised systems and fed into a gas mixer, which is calibrated to produce the exact ratios required for a given product. This is where science becomes critical – different commodities (for example, leafy greens versus meat) need different gas compositions to achieve optimal preservation without damaging texture, flavour or colour.
Attached to the mixer is a gas analyser, which verifies that the blended gas accurately matches the target composition. A miscalibrated mixture can undermine the entire process: too little oxygen risks anaerobic respiration and off-flavors; too little carbon dioxide may fail to adequately inhibit microbial growth; and poor nitrogen balance can lead to package collapse or suboptimal product appearance.
Once the correct mix is confirmed, this gas blend is flushed into the package around the product using a packaging machine. The package is then sealed to keep the modified atmosphere in place. After sealing, units pass through leak detection systems, which ensure no unwanted air movement occurs between the package interior and the external environment. Any significant leak would quickly erode the intended gas composition and nullify the benefits of MAP.
This carefully engineered process results in a final product with 5–15% carbon dioxide, about 1–5% oxygen, and 80–99% nitrogen, though the exact values depend on the specific produce. Importantly, maintaining an optimal – not minimal – oxygen level is crucial to avoid off-odours, colour changes and quality loss.
Understanding the MAP process mechanically is just the start. The real impact emerges when we see where MAP is applied across the food chain and how it changes the economics and logistics of handling fresh produce.
Next, we’ll explore the wide range of products that benefit from MAP – from vegetables and fruits to meat and salads – and examine how MAP transforms shelf life, quality and marketability.