Different Methods of Detecting Foreign Bodies in Food

Food manufacturers are very careful when it comes to detection of foreign bodies in food because it can lead to injury to customers. This, in turn, can cause loss of loyalty as well, recalls and rejections. These are bad for the business as it can cause loss of investments. Food safety and quality control are essential parts of the food industry. Manufacturers and producers invest millions in identification methods of foreign bodies. It can range from simple equipment to highly sophisticated ones. The most common methods are listed below:

Metal Detection
There are three types of metal detectors used in quality control in the food industry – pulse technology, ferrous in foil detectors and balanced three coil detectors.

Pulsed metal detectors are well suited for detecting large metal pieces such as nails and or cans in bags of raw materials. Ferrous in foil detectors, on the other hand, help detect ferrous metal contamination in foods with foil tray packaging. Balanced three coil detectors have high sensitivity, thereby, making it a favourite among the three types of metal detectors.

Balanced coil metal detectors are the most common type of metal detection equipment. It can detect the presence of metal shards in an unwrapped food or those in paper, poly film, cardboard and metalized film packaging.

Certain factors affect the sensitivity of metal detectors. The type, shape and orientation of metal play a role in the effectiveness of detection. The equipment’s operating frequency also affects the sensitivity. Other factors include position of metal in the aperture, type of product scanned, packaging material and environmental conditions such as vibration.

Magnetic separators are commonly used in the food industry. They are powered by permanent magnets of varying strength. There are two methods of producing magnetic fields – the use permanent magnets and electromagnets.

Many manufacturers favour magnets in detecting ferrous material in food because they are inexpensive and simple to use. Operators find it easy to install magnets and retrofitting requires lesser cost and minimal disruption. They are easy to maintain and clean as well. Any ferrous material detected can be easily collected and analysed, thus, reducing the incidence of metal ingression.

Magnets, however, can only detect ferrous contaminants. They are not effective in detecting phosphor bronze and brass. They are also not effective in detecting spherical objects. They also have difficulty removing contaminants embedded in processed foods such as cakes, bread, biscuits, and bottled products, canned and packaged foods.

Optical Sorting Systems
Optical sorting systems are automated techniques used to determined food quality by colour. The concept of human colour perception is used; however, the sorting equipment does the job of separating the unwanted objects using a specific range.

Optical sorting machines can detect different types of contaminants such as glass, sticks, stones, rotten materials insects, rotten matter, etc. Items that need to be scanned are passed through an optical box that can view objects from different angles. It measures the reflectivity of each object to detect any contaminants, defects or rejects.

Accuracy of the ejector’s performance depends upon the sensitivity of the machine. Increasing the sensitivity would result to more rejects or defects ejected, however, it can also increase the number of good products ejected. On the other hand, decreasing the sensitivity can result to more rejects allowed to join a batch.

Microwave Reflectance
Microwave imaging can cover a wide range of contaminants because of its power and sophistication. It covers very small contaminant particles and most of the time their location is easily identified. It does not have any restriction when it comes to manner of handling, flow speed of the subject within the detection equipment and the equipment does not pose any danger to the handling personnel and the subject material.

The greatest strength of a microwave detection system is the ability to detect a broad spectrum of contaminants in different conditions and packaging. However, the primary disadvantage of this method is the lack of resources as this equipment can only be found in limited number. Furthermore, in order to achieve such desirable features, current technologies need to be utilized. These technologies, however, are recently emerging and still awaiting availability.

Nuclear Magnetic Resonance Imaging
Nuclear Magnetic Resonance (NMR) and Magnetic Resonance Imaging (MRI) are ideal for detection of bone fragments and other foreign materials in meat, fish and poultry. Both can also detect foreign bodies in whole fruits and vegetables such as worms and holes. Furthermore, NMR can detect any disorders in fruits or vegetables. Internal browning, bruising, ripening, maturity, scald, rotten areas, fungal infection and even sugar content can all be identified using magnetic resonance imaging.

Magnetic Resonance Imaging is indeed a powerful tool in detection and assessment of food items. However, the greatest disadvantage is the high cost. Apart from the cost, manufacturers also find it inappropriate for most food production settings as it requires magnetic systems that are not really built for use in the food industry.

Surface Penetrating Radar
Surface penetrating radar uses electromagnetic radiation in detecting foreign bodies in food. It utilizes low power microwaves to scan a subject material and detect any variation in the dielectric properties between food and any foreign body contained in it. The difference in dielectric properties manifests as microwave signal delays. Any delay signifies the presence of a foreign material within a product.

Surface penetrating radars apply best for a quick quality check for the presence of required ingredients in a product (e.g. detecting peanuts in a chocolate with peanut bar). It is also applicable in detecting foreign bodies in different production levels. This eliminates the extensive checking for foreign bodies and contamination on the entire production process. Callbacks will be reduced if radar detection is set-up in the final stages of the production process. On the other hand, if it were set-up in the earlier production stages, it would help the producer avoid mixing the contaminants into the final product.

Using the radar method is effective for homogenous products with both metallic and non-metallic contaminants. However, its weakness lies in detecting contaminants within a metallic container or foil. The metallic packaging can impede the radar’s capacity to detect foreign materials, thereby, making it impossible to recognize any contaminants.

Electrical Impedance
Electrical impedance methods use three types of systems – capacitance, resistance and impedance. Electrical impedance detection systems are a cross between conventional metal detection systems and microwave-based systems. It works better than a conventional metal detector because it can detect non-metal items such as wood, plastic and glass.

This is made possible by the radio and microwave frequencies utilized by an impedance spectrometer. However, electrical impedance is rarely used in the detection of foreign bodies in food. If developers would only find more time to study its effectiveness, they would have come up with better detection equipment that can detect a wide array of foreign materials and missing parts.

Due to continuously changing baseline products, electrical impedance systems need to have a dynamic and well-updated measurement techniques and standards in place. This actually holds true with all detection systems especially if subject materials vary.

Using ultrasound in detecting foreign bodies in food entails fewer costs. It is also safer compared to X-ray. Many manufacturers and entrepreneurs favour ultrasound detection systems because they are non-intrusive and non-destructive to food products.

They are easier to operate under various conditions and test environments. These systems are also hygienic which conforms to food production and quality standards. Scanning food products under an ultrasound system is fast and easy so a high production rate is still maintained.

X-ray systems can detect various contaminants such as metals, non-ferrous metals, stones, glass, PVC plastic, bones, concrete, ceramic, Teflon plastic, sugar or flavour clumps and any missing products. X-rays are easy to operate and requires minimal training. High-end machines are even easier to operate with touch screen interfaces. Just like ultrasound systems, they can maintain high production rate with less false rejects.

However, X-ray machines cannot detect some contaminants such as paper, cardboard, wood, hair, insects, thin glass, low-density plastics and low-density stones.

X-ray systems are applicable in the production and quality control of meat, fruit, vegetables, cereals, dairy products, confectionery, ready meals, prepared foods and bakery products. An X-ray machine specifically used in food production is different from a diagnostic unit. It does not make the product radioactive. Radiation emissions are lesser compared to the latter.

Separation Systems
Separation systems are well suited for detecting contaminants and foreign bodies from raw materials and ingredients. Detection of foreign bodies in food is an important aspect in food production; because of this, much legislation has been implemented to protect consumers from potential health hazards of the inclusion of foreign bodies in food products.

Many food producers employ the use of sieving and filtration systems to uphold good manufacturing practice. Additionally, food producers are wary of complaints and lawsuits that can damage a brand’s reputation. Costs of lawsuits are also expensive and can exhaust a business’ financial resources.

Although sieving and filtrating cannot remove 100% of the contaminants, manufacturers and food producers can still sincerely claim that they have taken all possible precautions and that they practised due diligence during the production process.

There is actually no best method when it comes to detection of foreign materials in food. It depends upon several factors such as cost, type of packaging, subject material and other factors involved in production. In order to determine the most applicable and well-suited method for you, consider the factors affecting your production and business. Each of these methods has its own advantage and disadvantage. It is up to you to decide and weigh the pros versus the cons.



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