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In today’s world of instantaneous internet communication, a single consumer finding a foreign object in your food product can wreak havoc with your brand and reputation. Should the finding be considered potentially extensive, you could be facing a massive recall; and if a consumer is injured by the object, you could easily have a lawsuit on your hands.

According to Food Safety Management, A Practical Guide for the Food Industry (Elsevier, 2014) chapter authors Gilles Demaurex and Laurent Salle, a foreign object is “Any extraneous material in food not intended to be there or be consumed, e.g., field matter (stones, wood, metal) even if a part of the food itself (e.g., bone, shell, pits, stems, etc.); inadvertent processing residues (glass, metal fragments, plastic, personal objects, etc.); intentional contamination (e.g., employee sabotage); miscellaneous particulates and fragments.”

Intrusion can occur at any point along the food chain, and even if the foreign matter is not a hazard, “their finding in food may be indicative of poor hygienic practice and a distressing event for consumers,” the authors state.

Foreign material was the top reason for USDA recalls in the first two quarters of 2019, according to the Stericycle Recall Index quarterly data. While foreign material tends to place somewhere below allergens in FDA recalls, it was the top reason for recalls in at least one quarter in 2018. Additionally, guarding against foreign objects in food is mandated by U.S. regulation. As stated in the Food Code (21cfr110.80[b]8), “Effective measures shall be taken to protect against the inclusion of metal or other extraneous material in food. Compliance with this requirement may be accomplished by using sieves, traps, magnets, electronic metal detectors, or other suitable effective means.”

Because there are many potential stages at which foreign objects can get into food from the field to packaging, it can be advantageous to use a combination of methods to ensure against anything reaching the consumer.

One significant example is that of the Hazelnut Growers of Oregon’s seven methods of detection from field to distribution (Cover Profile. Hazelnuts: The Next Almond?).

DETECTION OPTIONS. So what methods are being used and what is best for your facility? While the specifics will depend greatly on the product, a wide range of controls can be customized to effectively control some of the risks of most processes. North Dakota State University graduate student Daniel Richard Dumas details common methods in his paper, “Foreign Material Identification and Removal in the Food Safety Industry”:

  • Filtering and Screening. Screens can separate solid foreign materials from liquid products or separate solid items based on size. Some require mechanical agitation or movement to allow for more effective product flow, but the basic method is that of creating a physical barrier to remove foreign material. The designs of these systems must account for known hazards and production speed. While generally low cost and high efficacy, screens and filters must be regularly inspected and maintained, as they eventually wear and break, potentially introducing metal into the system themselves.
  • Magnets. As the most basic level of metal removal used in the food industry, magnets can remove ferrous metals and are often used to identify upstream equipment failure and help protect product from machinery breakdown. Magnets can be ceramic for general use; Alnico magnets for high temperature processes that can exceed 400°F; and rare earth magnets which are the strongest and most effective, as they can remove magnetic stainless metals as well as weakly magnetic materials, but can vary in effectiveness at extreme temperature. Also used at safety control points downstream, magnets can remove many particles, including metal dust and pieces too small for identification by other methods, with little maintenance, cost, or product loss. A major disadvantage is that they can only remove magnetic materials. Other metals will not be removed from the product flow.
  • Optical/Laser Sorters. Optical and laser sorters can be used to remove foreign materials or items that do not meet quality parameters. These cameras or lasers can detect surface-level characteristics including color, shape, and moisture, and can distinguish biological characteristics. Once identified, an air jet or mechanical device can remove the nonconforming material. These sorters also can improve product quality through removal of discolored, damaged, and misshapen product.
  • Metal Detectors. Many facilities implement metal detectors as a final check of packaged product. Advances have continued with improvements in electronics, computers, and sensors, with metal detectors able to detect metal with high efficiency. The basic operation occurs by one of two methods: a balanced coil system using electromagnetic induction or a magnetic field system. These systems can be limited due to the material that is being tested and the type of metal that is targeted. In materials that have higher conductivity levels, it can be more difficult to identify metal using balanced coil systems, while magnetic field detectors can identify magnetic metal inside aluminum cans. Basic detectors are common in the food industry, and industrial versions continually advance to improve the level of detection and accuracy; remain cost-effective while reducing false trips and product loss; increase operation in environmental conditions such as heat, vibration, and moisture; and reduce cross-signal effects from other machinery or communication equipment. However, if a food process has other inherent risks or the facility wishes to identify non-metal foreign materials, additional or alternative methods will need to be implemented.
  • X-ray. X-rays use short wavelengths that can easily penetrate packaging materials and enable detection of foreign materials in packaged products. These detectors use high-powered energy sources and imaging systems to produce images of the material and identify foreign materials. The ability of X-ray devices to detect even small differences between food and foreign material, including metal, can be more effective than that of metal detectors. Additionally, X-ray can detect and identify plastic and glass, and can operate at relatively efficient processing speed. The ability of X-ray to detect foreign materials is continually improving and allowing for more sensitive identification. Some developments, such as the use of dark field imaging, are being attempted to increase their ability to detect organic materials on a smaller scale. X-ray use is currently limited by the cost of the units and maintenance, processing speed, and safety aspects some associate with the radiation. These areas are being improved as advancements are made and costs are reduced.
  • Visual Detection. Visual methods include various wavelength or imaging sources. A basic optical method of reflectance measurements uses the visible light spectrum. A light source is used to create a reflectance off the surface of the product and enable differences between food and foreign material to be detected. This method has been shown to help in the removal of sticks, stems, or rocks. Some limiting factors are the heat caused by the illumination and its ability to detect only surface materials, which make testing of sensitive, thick, or bulk materials impractical. Other visual detection methods include testing with near-infrared wavelengths of light which use the absorption ratios of molecular bonds to differentiate the different materials within a sample, and ultraviolet wavelengths using radiation of the product and the signal that various materials will reradiate. These methods vary with efficiency depending on the food product and target foreign material.
  • Hyperspectral Imaging. Hyperspectral imaging combines spectroscopy and digital imaging computers. The visible spectrums and multiple-spectral wavelengths can be customized to detect foreign bodies that do not share similar patterns and to identify quality parameters such as bruised produce and ripeness. Due to its speed and wavelengths that can be incorporated, there are many other potential avenues for which this method may be helpful in the future, however additional research into computations and filters will be needed.
  • Thermal Imaging. Thermal imaging typically occurs in one of two ways: If the product and/or foreign material gives off heat at a suitable range, infrared energy can be applied and the difference between the two used to create a digital image, in which foreign material can be detected. The other method is the application of heat in a short burst, with the distance into which the heat is able to penetrate measured. This creates a contrast that enables the detector to identify the foreign material. These methods may not be suitable for all food products but may be able to be adapted to processes where heating or heat treatment of products is already occurring.

EQUIPMENT SELECTION. With such options, how does the food facility determine the best equipment by which to detect and prevent foreign object intrusion? As Demaurex and Salle explain in their chapter, several aspects will determine the choice of detection equipment, such as contamination risk, packaging and product characteristics, line layout, environmental conditions, or process speed. But, the authors add, no technology can detect all types of physical hazards. Following is the authors’ recommended selection process (with updates for relevance):

  1. Determine the source and nature of physical hazards along the production line. Your HACCP (and FSMA Preventive Controls) plans, plant records, maintenance reports, and consumer complaints can all be helpful.
  2. Apply all possible prevention measures to reduce foreign bodies (GMPs, hygienic design, best practices, sorters) according to the principle “first prevent, then detect.” Working on the hygienic design of equipment with the supplier will deliver better results than simply using a metal detector to detect equipment issues.
  3. Select the most appropriate technology and location according to the type of product and the packaging. This might require modifications to the line layout. For example, the installation of a metal detector before filling instead of an X-ray device on packed product might require a redesign of the filler infeed or height of the building. Keep in mind that metal detectors and X-ray technology are more effective on small products (e.g. bulk before filling or individual packaging), than on grouped products or shipping cases.
  4. Select a short list of potential suppliers, based on criteria such as best detection performance for the specific application; ability to provide turnkey solutions (infeed, product handling, reject, etc.); support level available; and coherence with other equipment brands already installed in the plant to optimize maintenance and operational cost.
  5. Build a user requirement specification (URS) and send this with products and contaminated test samples to the preselected suppliers for detection capabilities trials. It is recommended that you build your own sets of contaminated test samples to ensure a fair performance benchmarking between suppliers (with spheres and real fragments). Indicate the testing procedures to follow. Ideally you should be present during the trials.
  6. Build a selection matrix to make the choice, assessing the key elements of the URS. For example, equipment with slightly inferior performance might be chosen for its ease of cleaning and hygienic design.
  7. Conduct a detailed performance qualification with the selected supplier to assess and document the detection capabilities for each relevant foreign body type.

Regardless of the number and types of methods and equipment implemented, many food facilities choose to supplement them with human visual quality and safety checks. While this cannot detect internal, imbedded material, the idiomatic phrase “an extra set of eyes” can be the very difference between customer satisfaction and a federal inspector knocking at your door.

The author is Editor of QA magazine. She can be reached at llupo@gie.net.