X-ray Inspection Systems in Food Processing Plants

Following Good Manufacturing Practices (GMPs) and a well developed Hazard Analysis Critical Control Point (HACCP) plan can help prevent, reduce or eliminate foreign contaminants in raw materials and finished products. Depending on your product and packaging, technology such as x-ray inspection systems can assist you as a tool within your foreign materials reduction program.

X-ray Inspection Systems

X-ray inspection systems are based on the density of the product and the contaminant. As an x-ray penetrates a food product, it loses some of its energy. A dense area, such as a contaminant, will reduce the energy even further. As the x-ray exits the product, it reaches a sensor. The sensor then converts the energy signal into an image of the interior of the food product. Foreign matter appears as a darker shade of grey and helps identify foreign contaminants.

Ideally, x-ray inspection should be done at several locations along the production line. Only inspecting at the beginning of the line means contaminants introduced at a later point on the line won't be detected. The best location for x-ray inspection is at the end of your production line.

Benefits and uses

The benefit of x-ray inspection is the ability to identify possible foreign contaminants in your product. This reduces risk of customer complaints and possible recalls. X-ray inspection systems are known to detect:

  • all types of metals
  • calcified bones
  • ceramic or concrete
  • glass
  • non-ferrous metals in foil
  • PVC plastic
  • rubber
  • stainless steel
  • stones
  • teflon

The detection capability of contaminants is directly related to the density of the product and the contaminant. The denser the contaminant, the darker it will appear on the image and the easier it will be to identify. There are some contaminants an x-ray system may not detect, including:

  • cardboard
  • hair
  • insects
  • low density plastics
  • low density stones
  • paper
  • soft bones (cartilage)
  • wood
  • thin glass (such as fluorescent tubes)

X-ray inspection systems are commonly used to monitor product quality. For example, they can be used to measure mass or density and can indicate that a package is under or overfilled. Other uses include monitoring for broken or damaged product, missing product components and head spacing in packaging.  

Considerations when choosing an x-ray inspection system

1. Needs

Choose an x-ray model based on the size, weight and shape of the product, and the line speed. X-ray inspection systems have unique monitoring capabilities that metal detectors don't have. Examples include:

  • They reveal metal contaminants in food products that are packaged in metal containers, wrapped within a metal film or containers with metal lids.
  • Food products with high salt and/or moisture content that normally reduce the sensitivity of a conventional metal detector can be monitored.
  • Non-metallic dense contaminants, such as glass or stones, are detected.

2. Type of product

The success of x-ray inspection systems depends to some degree, on the food product. The thickness, homogeneity, density and size of the product determine the accuracy of detection for contaminants. X-ray inspection systems work better with homogenous products, like cheese, because they create clearer images of background interference. Non-homogenous products, like canned soup, will create uneven shades of grey and could give false readings, because soup can have different components with different densities.

X-ray inspection systems are not affected by product temperature. They are successfully used to inspect products at — 20 °C or + 90 ° C.

3. Automated versus manual inspection

The main difference between manual and automated systems is how the food items are handled and where the defect decision is made. In manual systems, the operator loads and unloads the food item from the machine and makes the defect decision based on the x-ray image. All manual systems include image enhancement hardware, which will electronically enhance the image. This is helpful because the defect decision is being made by the operator visually, so any tools to aid the human eye will reduce the chance of human error.

In automated systems, the food item may be automatically loaded by a conveyor or by an operator. Automated systems use software to make the defect decision and do not rely on the operator's vision. The software compares the x-ray image with preset measurements and rejects defective products automatically. If a product is rejected, it can be removed with an automated rejection mechanism such as:

  • air blow-off systems
  • drop flaps
  • retracting conveyors
  • sweep arms  

Safety of x-rays

X-ray inspection systems are safe to use in the food industry. However, they must meet strict regulatory standards for operator safety.  Some of these requirements include:

  • safety to protect operators when using the machine
  • mechanical safety design of the machine
  • emitted radiation levels

For more information, email the Food Safety and Inspection Branch or call 204-795-8418 in Winnipeg.