A non-destructive measuring device in the mid-infrared range for measuring the CO2 concentration in the headspace of food packaging

Carbon dioxide (CO₂) is the most common gas used in modified atmosphere packaging (MAP) to protect packaged foods from spoilage and pathogenic microorganisms and thus extend the shelf life of food products. Non-destructive measurement of CO₂ concentration of the packaging headspace is of great interest as it could be used at various stages of the value chain, from outgoing goods inspection to storage tests and possible monitoring of the modified atmosphere at retail. Therefore, the aim of this work was to develop a measuring device operating non-destructively on closed MAP trays. Absorption measurement in the mid-infrared range at four different wavelengths proved to be a suitable principle for determining the CO₂ gas concentration in a closed packaging system: 4.26 μm (2347 cm⁻¹) and 4.27 μm (2342 cm⁻¹) in the range of the antisymmetric stretching vibration, as well as 4.45 μm (2247 cm⁻¹) at the edge of the antisymmetric stretching vibration, and 3.95 μm (2532 cm⁻¹) as a reference measurement outside the absorption band with a thermal infrared source. Measurement principle and setup - the measurement in the absorbing and non-absorbing range and the guiding of the thermal infrared (IR) emitter at a 45° angle through the corner of the tray - allows a measurement largely independent of tray shape, height, and packaged product. The measurement can also be used for pigmented and printed trays - except for carbon black pigments. Optical impairments of the packaging and labeled areas of the lidding film appeared to have the greatest influence on the measurement accuracy. The applicability of the measurement system was evaluated and successfully demonstrated using commercially available food packaging from a local supermarket by comparing the CO₂ gas concentrations yielded with those obtained using a destructive measurement device.