Increasing regulatory and consumer demands have intensified the pressure on the food industry to implement reliable methods of food inspection to ensure product safety and quality. Xray technology can be used in food inspection to detect physical contaminants and to study the internal structure of food products for quality purposes.
The operation of food safety management systems incorporates the principles of Hazard Analysis and Critical Control Points (HACCP); inspection forms a key part of procedures designed to control potential hazards. The role of technology for inspection purposes has become increasingly important due to the everincreasing emphasis by consumers and regulatory authorities on food safety and quality. Emerging issues such as fraud and the intentional contamination of food have also highlighted the importance of food inspection technology.
Many different methods and technologies are available for the inspection of food, including metal detectors, optical camera systems, magnetic resonance imaging, ultrasound, and Xrays. The
application of a specific inspection technology is related to the nature of the food and the specific purpose of that inspection.
Xrays are a form of invisible electromagnetic energy with short wavelengths and high energies. The use of Xray technology is most familiar to people through its use in medical imaging. However, Xrays can also penetrate food products and allow the imaging of the internal features of the food to detect physical defects or contaminants without damaging the food product.
As an Xray enters a food it loses some of its electromagnetic energy. If the Xray encounters a dense area in the food, such as a metal contaminant this will reduce the Xray energy further. As the Xray leaves the food a sensor in the inspection equipment converts the Xray into a greyscale image of the foods interior. The denser a contaminant, the darker it will appear in the image, which helps in its identification
Uses of x-ray inspection
Depending on the type of Xray inspection equipment and the nature of the food product, Xray inspection can identify a variety of physical contaminants including metal, glass, rubber, stone and some plastics. Because Xray inspection provides nondestructive imaging, its use has become more widespread for packaged, processed foods, particularly those in bottles, cans, jars and pouches. Increasingly, as the technology advances Xray inspection is being used for inline production control and verification.
Considerable research has highlighted the potential of Xray inspection for the grading of fruits, vegetables and grains, and detection of bones in chicken and fish. Some advanced Xray inspection systems can simultaneously perform inline quality checks detecting physical defects, measuring mass, counting components, identifying missing or broken products, monitoring fill levels and inspecting the seal integrity of packaging. As such Xray inspection systems may help reduce inspection costs for some food businesses.
Disadvantages of x-ray inspection
Xray inspection has a number of distinct disadvantages including its relatively high cost and the need for high voltage power supplies to generate Xrays. Xray inspection also has a number of perceived disadvantages, e.g. the perception that Xray inspection irradiates food. However, the Xray dose used for inspection purposes is significantly lower than that for irradiation and does not affect the safety, quality or nutritional value of foods.
Concern has been expressed that operators may be exposed to harmful levels of radiation from Xray inspection systems. However, under normal circumstances the level of radiation that an operator in direct contact with an Xray system will receive is less than that received in a year from natural background radiation.
As the capability of Xray inspection to detect contaminants is directly related to the density of the product and the contaminant, there are some contaminants which Xray inspection systems have difficulty in detecting and imaging. These include hair, paper/cardboard, low density plastics and stone, string, wood and soft bone tissue such as cartilage. Other inspection technologies and controls are often used to identify these low density contaminants. However, advances in Xray inspection technology and particularly coupling of other technologies to improve imaging are addressing some of these limitations.
The detection of physical defects and contaminants using Xray technology is an important part of quality control for specific food businesses. While technological advances have made Xray inspection systems more affordable, reliable, and easier to use, with improved image quality and detection capabilities, they still remain costly.2 However, continuing advances in Xray inspection should ensure that use of this technology expands within the food industry.
1. European Commission (2012). The rapid alert system for food and feed annual report, 2011: http://ec.europa.eu/food/food/rapidalert/docs/rasff_annual_report_2011_en.pdf
2. Haff RP & Toyofuku N. (2008). Xray detection of defects and contaminants in the food industry. Sens Instrumen Food Qual 2:262–73.
3. Graves M et al. (1998). Approaches to foreign body detection in foods. Trends Food Sci Technol 9(1):21–7.
4. Mery D et al. (2011). Automated fish bone detection using Xray imaging. J Food Eng 105(3):485–92.
5. World Health Organization (1999). High dose irradiation: wholesomeness of food irradiated with doses above 10kGy: http://www.who.int/foodsafety/publications/fs_management/en/irrad.pdf
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