Detecting Foreign Bodies in Food

Detecting Foreign Bodies in Food

Edited by Mike Edwards

Woodhead Publishing Limited; Cambridge, England
Corporate Blvd, NW, Boca Raton, FL  33431
Tel: 1-800-272-7737 | Email:

CRC Press order number: WP2546
ISBN 0-8493-2546-3
306 pages, Illustrated
Price: US $199.95

“Foreign bodies are the biggest single source of customer complaints for many food manufacturers, retailers and enforcement authorities….” So begins the preface of this book, a unique collection of essays covering the sources of foreign body contamination in foods, their prevention, detection, remediation and identification, and even the role of quality control management dealing with publicity and public relations issues.

This book grew out of a FoodLINK workshop organized by DEFRA [the Department for Environment, Food and Rural Affairs, an English government organization dedicated to promoting sustainable agriculture; FoodLINK is an English organization dedicated to food safety] in 2002, the purpose of which was to “evaluate the current state of art in the field, identify gaps in capabilities and to assess new technologies.” Thus, it appears that a major purpose of the symposium was to establish order in a field that had been growing in a somewhat ad hoc fashion, and, in the same vein, the book lays out the managerial responsibilities currently at play, and surveys the technological tools currently available to food processors in contemporary European and other advanced societies, and to encourage the implementation of promising new methods. This book is an invaluable reference for professionals in the food processing industry.

Several chapters in Part I primarily address managerial issues:

Chapter 1: “Identifying potential sources of foreign bodies in the supply chain”, R. A. Marsh and R. E. Angold, RHM Technology, UK.

This chapter provides a good general introduction to the food processing chain, from prime producer, through transportation, processing, the various stages in manufacturing, through packaging, distribution, purchase, preparation and finally consumption.

Chapter 2:  “GMP, HACCP and the prevention of foreign bodies”, R. R. Gaze and A. J. Campbell, Campden and Chorleywood Food Research Association, UK.

The implementation of good manufacturing practices (GMP) and of hazard analysis and critical control point (HACCP) systems is addressed as a 12-stage process.

Chapter 3:  “Managing incidents involving foreign bodies”, T. Hines, Leatherhead Food International, UK.

When a foreign body crisis does occur, it is management’s responsibility to respond appropriately, both to protect the health and rights of the consumer, and to minimize damage to the food processing industry as a whole.

The bulk of the book, Part II, surveys methods and instrumental techniques for the detection and identification of foreign bodies, as well as strategies for their removal.  A brief description of each follows:

Chapter 4: “Metal detection”, J. P. Craig, Thermo Electron Corporation, UK.

Metal detection is based on the transmission and reception of electrical impulses, based on their conductivity and magnetic properties.

Chapter 5: “Magnets”, E. Apoussidis and I. Wells, Eriez Magnetics Europe, UK.

Magnets can remove unwanted ferrous materials both simply and inexpensively. Both permanent and electromagnets are discussed, with a number of specific applications.

Chapter 6: “Optical sorting systems”, S.C. Bee and M.J. Honeywood, Sortex Ltd, UK.

Optical sorting systems consist of four principal components: the product feed control, the optical sensors, the image processing module, and the foreign body ejection mechanisms. Monochromatic and dichromatic systems are discussed, as are low pass, high pass and band pass filtration systems for their implementation.

Chapter 7: “Applying optical systems”, G. Doménech-Asensi, Polytechnic University of Cartagena, Spain.

This chapter discusses several applications of the principles elaborated in the previous chapter, especially in the collection, sorting, and dissemination of agricultural products. The importance of appropriate illumination methods is strongly emphasized, as good illumination can help the sensors (human or instrumental) sort the good from the bad apples (or other produce).

Chapter 8:  “Microwave reflectance”, R. Benjamin, University of Bristol, UK.

The author considers this method potentially one of the most promising. A very large number of materials differ noticeably from contaminants in their specific microwave impedance, very small particles are detectable, their positions can be resolved in three dimensions, flow speed is not a restricting factor, the radiation is safe both for workers in the area and the subject material, and the costs for the technology are reasonable. While transmission methods have been successfully employed, holography utilizing reflected or back-scattered techniques or, even better, surface-penetrating radar of high range resolution has many advantages. The main challenge is capturing a sufficient amount of data to provide adequate sampling.

In spite of the many potential advantages of microwave reflection food product inspection, this technology is only now emerging, and exists only as a concept; commercial systems are yet to be implemented.

Chapter 9: “Nuclear magnetic resonance imaging”, B. Hills, Institute of Food Research, UK.

We are well acquainted with NMR in its applications as a medical imaging tool (then called magnetic resonance imaging, or MRI) and as NMR spectroscopy for research and analysis; in this chapter, the author reviews some of the reasons why NMR “…has not yet penetrated the industrial production line as a foreign body and quality control sensor and, on a more optimistic note, point out some of the ongoing research directed at overcoming these limitations.” The essential problem facing the development engineer is the amount of time necessary to acquire a full, three-dimensional image. The price paid for shorter acquisition times is lower signal-to-noise ratios and therefore lower spatial resolution.

Chapter 10: “Surface penetrating radar”, U-K. Barr, SIC and H. Merkel, Chalmers University of Technology, Sweden.

This chapter would be better juxtaposed with Chapter 8, in which the use of radar is also discussed. Chapter 10 explores the mathematical foundations of radar imaging at the scale, and speeds, that radar usage would require when and if it is ever implemented as a food inspection technology.  While not yet implemented on a commercial scale, small scale tests have been conducted with promising results, especially with highly homogeneous materials. For example, it was found that metal foreign bodies in wet, homogeneous materials were easier to detect than pieces of plastic in the same products. For less homogeneous materials, higher levels of instrumental complexity would be required.

Preliminary tests of microwave radar have shown that it can detect materials such as stone, glass, stainless steel, and plastic in uniform products as small as 1 mm x 1 mm x 2 mm. The method is unsuitable for products in metallic or foil-wrapped containers.

Chapter 11:  “Electrical impedance”, R. Dowdeswell, Kaiku Ltd, UK.

This chapter addresses methods of foreign body detection that work by measuring the changes in the electrical properties of the
inspected objects. Currently, no commercially available systems exist, so the data discussed in this chapter are based on prototype systems, or systems modified from other applications. Technologically, the system is intermediate between conventional metal detection systems and microwave-based approaches.

Chapter 12: “Ultrasound”, O. A. Basir and B. Zhao, University of Waterloo and G. S. Mittal, University of Guelph, Canada.

“Foreign bodies are different from food in terms of acoustic impedance, which is the product of their density and sound velocity in a give material. Reflections, refractions and scatterings take place due to discontinuity in acoustic impedance along the sound propagation path through the food medium.”

Ultrasound is recommended as a promising technology, especially for cost-effective inspection of beverage containers, but is not currently employed. This chapter explores some of the theoretical aspects of ultrasound as well as a number of experiments that show considerable promise.

Chapter 13:  “Using X-rays to detect foreign bodies”, B.G. Batchelor, Cardiff University, E. R. Davies, Royal Halloway, University of London and M. Graves, Spectral Fusion Technologies, Ltd., UK.

“X-rays have been used to inspect food for the presence of foreign bodies since the early 1970s…. In this chapter, we review the way that X-rays are generated; how they are attenuated as they pass through a medium; how they are detected to form digital images and how these images are processed by computer. We also describe several typical applications.” As the author notes, this is a relatively mature technology, and his discussion is thorough and candid. I especially like his Appendix in which he lists a number of factors that affect system performance.

Chapter 14: “Separation systems”, R. O’Connell, Russel Finex Ltd, UK.

Methods for separating the foreign bodies from the foodstuffs, or the packages containing foreign bodies from clean ones, are
discussed in many of the other sections of this book, but it was appropriate to include a separate chapter devoted to addressing the subject in detail. This chapter is highly practical – the word “conscientious” comes to mind–discussing in detail strategies for separating many different kinds of foreign bodies from the intended foodstuffs. His emphasis is on sieving and filtering systems, appropriate to his professional affiliation.

Chapter 15:  “Identifying foreign bodies”, M. Edwards, Campden and Chorleywood Food Research Association, UK.

Microscopists will find this chapter completely familiar territory. The author introduces his basic approach with the following series of questions:

    1. What is it?
    1. What is it precisely?
    1. Where did it come from?
    1. How did it get into the food?
  1. Has it been processed?

I especially like the first two questions, because they so emphatically summarize our roles as microscopists: not only must we identify the general class, but the specific type as well. The author emphasizes careful initial study with the stereomicroscope, then further analysis with the compound microscope (preferably a polarizing microscope), with additional analysis, as appropriate with various stains and reagents, spot tests, infrared spectroscopy, or energy dispersive x-ray spectrometry or x-ray fluorescence, depending on instrument availability. He describes a few tests in detail, especially the alkaline phosphatase test, to determine whether insects found in a foodstuff have been heat processed.


This book provides an in-depth survey of managerial and engineering approaches to the problem of foreign bodies in food, whether currently in use or as promising technologies. The intended audience for this book is clearly managers and engineers in the food processing industry, but microscopists, especially those in food applications, might also benefit from this study. Although this book may seem to be concerned primarily with “macro” issues, many projects over the years have involved foreign body identification, some bona-fide, and some in which attempted fraud was uncovered by microscopical analysis, so background information in this field can often be useful. I was especially impressed with the editorial design, and was most pleased to see that the editor is also the author of the last chapter, and is, therefore, a microscopist.


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