Millions of pounds of meat are recalled every year due to foreign object contamination. For the poultry industry, there’s the added complication of bone fragments as an additional foreign body on top of the standard metal and glass contaminant risks.
Since poultry products take many forms – from whole turkeys to chicken nuggets and everything in between – there are a variety of inspection options during the production process. So how do you decide where to install contaminant detection equipment to provide the greatest security with minimum wastage?
X-ray inspection uses the fact that different atoms absorb X-rays in differing amounts. Therefore, protein will appear differently in an image to metal, bone or glass. The darker regions caused by these foreign objects can then be detected using image analysis software – and any product showing signs of contamination can be immediately removed from the process.
For bone-in products, inspection should be as late in the process as possible – ideally once the product is sealed, to prevent any further contaminants being introduced. By designating a high-risk, unpackaged area and a low-risk, packaged area, X-ray can act as a ‘gatekeeper’ to allow only compliant products through. Even in whole birds, microscopic metal contaminants can be detected and removed from the product flow.
For products expected to be bone-free, however, the situation is more complicated. Inspection of sealed containers at the end of a production line is useful as it ensures no new contaminants can be introduced. However, if value has been added – by creating chicken nuggets, for example – then it might not be possible to rework rejected products. Instead, it is preferable to detect bone much earlier in the process – ideally while the meat is still whole muscle.
The natural variation between birds, however, and the automated preparation of chicken breasts, means the resulting muscle is not uniform. The varying thickness and uneven presentation can make it difficult to detect bones, which are low density and hollow. This has led to the growth of dual-energy X-ray systems.
Dual-energy systems generate two images – one produced by high-energy X-rays and the other from low-energy X-rays. Since bone and muscle are made from different atomic constituents, they respond differently to the two energies. This allows the system to differentiate between variation in thickness and the presence of bone – leading to more sensitive detection. A well set-up system can detect rib and fan bones of less than 6mm, for example. Having identified any bones left in the product, the items can be reworked easily to minimise product wastage.
If the product is to be sold as whole breasts, these items can then be packaged and move from a high-risk to a low-risk area, via a second X-ray system to confirm the absence of metal, glass or other contaminants in the sealed product.
For processed products, the muscle is often passed through a pipeline, which provides a good opportunity for X-ray inspection. Rather than using dual energy to compensate for the variation in product thickness, the predictable cross-section of the pipeline can be used to give a uniform inspection. This uniform presentation allows for excellent sensitivity against bone – wishbones a few millimetres in length, for example – and submillimetre sensitivity for metal contaminants. Additionally, the rejected product can be diverted into a mechanical separator, removing the bone fragment but preserving the protein – ensuring there is minimal waste.
If the product has passed through a grinder, the X-ray system can be configured to ignore bones below a certain size while still rejecting larger bones. This can provide useful feedback for whether the grinder is operating as expected. Further in the process, this material may be formed into nuggets or other shapes. Wide-format X-ray inspection lends itself to positioning directly after this, where the product is separated into individual items. But belt widths of a metre are common – requiring specialist X-ray equipment.
Inspection at this stage can verify an individual item’s shape and mass – ensuring every nugget is exactly the same weight, for example – and check there has been clean removal from the mould; all while allowing for the detection of microscopic metal contaminants, as well as glass and bone fragments. A multilane rejection system or air curtain allows for the removal of a single item. Contrast this with inspection once bagged, where a single rejection results in the removal of dozens of items.
A final inspection after packaging is also valuable – and allows a final count of the number of items leaving the production line.
Bio
DrRichard Parmee is founder and CEO of X-ray inspection technology specialist Sapphire Inspection Systems. As well as designing bespoke solutions, Richard and his team provide a wide range of standard X-ray inspection systems to cater for hundreds of different products in the food, pharmaceutical and cosmetics industries.