Sounding out foreign objects in food

A new ultrasonic technology could tell ice cream manufacturers if any lumps in their product are something less desirable than chocolate chips. The foreign object detection technique could also be used in quality assurance of other food process streams.

Researchers at the US Department of Energy’s Pacific Northwest National Laboratory (PNNL) have developed a patented inspection method that uses sound waves to detect foreign objects in processing streams. Originally developed to look for bone fragments and foreign materials in chicken breasts, the method can also detect cartilage, metal and plastic; essentially anything that shouldn’t be in the product. Battelle, which operates PNNL, funded the research.

A process stream is typically a continuous flow of slurry or liquid that goes through multiple steps on its way to becoming a finished product. During processing, objects can fall into the mixture, bones can be left in meat, or pits and seeds may be left in fruit.

The PNNL-developed method combines both ultrasonic and optical capabilities.

“Our method is the only one we’re aware of that uses both acoustics and optics,” said Aaron Diaz, PNNL staff scientist. “Because it can be automated, it’s inherently safer and more effective than inspecting certain types of process streams manually. And automation eliminates the need for costly and slower inspections using methods such as X-ray, which typically requires added safety precautions and complex operator training.”

Acoustics, combined with transmitted light through the product, enhances the data available from the stream, making results more accurate. The two methods can also be used separately, depending on the properties of the product being inspected.

“Our process involves multiple sensors configured along the process stream,” said Diaz. “We flood the stream with sound pulses of acoustic energy, while at the same time transmitting optical energy. We’re looking for reflected echoes that we can correlate with location, such as depth and lateral position, in the stream relative to the product’s flow rate. If the received acoustic response is abnormal, it indicates there’s something in the stream that shouldn’t be there and we know, generally, where the foreign object is.”

Unwanted natural objects can also occur in a process stream. In chicken breasts, for example, components of the raw materials may be unintentionally left in the breast during a separation process.

The challenge in using acoustics to examine chicken breasts is the innate presence of air bubbles within the chicken slurry. These bubbles reflect sound energy. The reflections may be interpreted as bones or other materials, making the PNNL-developed method ill-suited for its original purpose. But baby food, other puréed foodstuffs and ice cream can be examined with this method.

“Although the original application presented some challenges and, ultimately, didn’t work out, it’s a useful technology that could positively impact manufacturing in many other areas,” said Diaz.