Improve contaminant detection and food safety with Dual Energy X-ray

With certain products, food manufacturers can realise great benefits from using dual energy x-ray detection. Mike Pipe, Head of Global Sales of Mettler-Toledo Safeline X-ray, explains how the technology can improve both inspection and business performance. 

The detection of foreign body contaminants is part of the critical quality assurance process to improve food safety standards. X-ray inspection has long been a key technology in this process, but there are different types of x-ray detection with which food manufacturers can inspect their products, depending upon the nature of the application.

Traditionally, manufacturers have used single energy x-ray detectors, but dual energy technology is becoming more commonplace, and is more powerful, effective, and easy to use than ever before.  It works using the concept of ‘material discrimination’, with dual x-ray beams of different energy able to identify materials of different densities. Advances in detection sensitivity mean that dual energy x-ray is now even more discerning, allowing ever-smaller contaminants to be detected in a wider range of applications.

But what are the applications in which dual energy x-ray excels compared to the more commonplace single energy detection systems? In simple terms, there are two key aspects of a product that make it suitable for inspection by dual energy x-ray. The first is where there is a large degree of overlap within the package, or where there are variations in thickness. Examples of the types of packs where products overlap include packs of pasta, rice, nuts, and frozen goods such as French fries or potato wedges. Packs with variations in product thickness include chicken breasts and other fresh cuts of meat. Both scenarios produce an x-ray image with high levels of contrast.

The second type of application where dual energy x-ray is most suitable is where the likely contaminant in a food product is a low-density material, such as glass, plastic, rubber and calcified bone.

If a product application has one or both of these aspects, then a case can be made for dual energy x-ray. However, it is important to understand how this technology works. Here, the key concept is material discrimination.

Dual energy x-ray works by using high and low x-ray energy levels to discriminate between materials of different densities.  Software algorithms enable the material that is the food product to be removed from a noisy x-ray image, leaving behind any material identified by the second energy level. This is most likely to be a contaminant.

The most advanced dual energy technology available today features an enhanced detector that collects detailed data about the product being inspected. When this is combined with sophisticated image analysis software, the result is even clearer, higher resolution images that enable the best levels of contaminant detection possible today.

Best fit 

Mettler-Toledo dual energy x-ray systems can detect more than eight times as many difficult-to-find contaminants as single energy x-ray systems. To ensure that a manufacturer’s application is best suited to dual energy x-ray manufacturers should look for a “Test Before You Invest” service.    

The general rule of thumb is that dual energy is best suited to applications where some or all of these factors exist:

• the product being inspected is one with high contrast, caused by overlapping products or products with variable thicknesses

• the expected contaminants are low density materials such as glass, rubber, plastic and calcified bone

• the packaging material used is low density, allowing low energy x-rays to pass through and inspect the product inside

Improving the effectiveness of contaminant detection with dual energy x-ray that is optimised to the product application is clearly beneficial to food quality and consumer safety standards, but it also helps the food manufacturer’s business.

Consider, for example, the degree to which the sensitivity of a single energy x-ray system would have to be fine-tuned to detect very small contaminants such as 0.8mm pieces of stainless steel in packs of nuts. The sensitivity required for such an application would very likely cause many false rejects, which would result in a great deal of product throwaway. Turning down the sensitivity to reduce the false reject rate might mean that contaminated products pass undetected, leading to a product recall and damage to reputation. Using dual energy x-ray would very likely enable the manufacturer to optimise detection around this application, without the resulting surge in false rejects and wasted products. In turn, this makes the business case for dual energy x-ray much stronger.

Balancing wants and needs

Food manufacturers have to balance a range of factors, including budget constraints, when deciding upon investments and improvements to their production line capabilities, and product inspection is only one of their considerations. It is a critical one though since it is the guardian of food safety.

With dual energy x-ray, everything depends upon the application, including the nature of the product, the possible contaminant, and the packaging. If operating on a tight budget, a single energy x-ray system might seem superficially more attractive. However, the more advanced contaminant detection capabilities of dual energy make more accurate inspection of challenging applications possible, and can quickly provide a return on investment, when set against the mounting costs of waste through false rejects and potential product recalls.