Non-invasive detection of internal foreign bodies in foods by using air-coupled ultrasound: case studies in beef burger patties and jelly plates

The detection of foreign bodies in the food industry is of increasingly critical importance due to potential health hazards to consumers, adverse effects on company's reputation, and legal compliance concerns. Therefore, this work aimed to assess the feasibility of using air-coupled ultrasound to detect foreign bodies within beef burgers patties and jelly plates as heterogenous-solid and homogeneous-semi solid model foods. Different types of foreign bodies (metal and plastic) at two different sizes (10 and 5 mm) were embedded within the burger patties and jelly plates. Both Control and Out-of-Control (OC, with foreign bodies) samples were scanned using an automated 2D system and a pair of unfocused air-coupled ultrasound sensors (0.28 MHz) operating in through-transmission mode. From time-domain ultrasound signals, two energy-related ultrasound parameters (square norm and integral) were computed to create the ultrasonic images. The presence of foreign bodies within the food samples led to the attenuation of the ultrasound waves (avg. square norm and integral decrease from 94.4 to 41.0 %, depending on the food product and foreign body size and material). This enabled the mapping of defective areas in both square norm and integral ultrasonic C-Scan images. Histogram-based image analysis proved to be effective in distinguishing between control and OC samples, while also facilitating the establishment of a detection threshold for foreign body identification. The manuscript also illustrates how the use of unfocused air-coupled ultrasonic transducers may be extrapolated for industrial purposes by minimizing the number of array elements necessary to scan the whole product. The methodology proposed in this study offers significant promise for the reliable, rapid, and accurate detection of foreign bodies in solid and semi-solid food matrices, with great potential for further industrial implementation.