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Physical contaminants

Identification of physical contaminants in food

By Mike Edwards - 30 January 2012

The rapid and cost-effective identification of foreign bodies reported from food is an essential part of the investigation of contamination incidents in order to reassure the complainant and help to prevent a recurrence. We have offered a service for the identification of glass fragments and other foreign bodies for many years, and have a wealth of experience to bring to each case.

An important part of this process is the gathering of initial data on the find, usually by the retail store to which the complainant takes their find. Full details of the precise circumstances of the discovery can often be crucial in the correct interpretation of the evidence - was the foreign body found in the pack, or on the plate? Had it been in the complainant's mouth? Is the original packaging available for inspection? What was the date of the discovery ? (not just the date of the complaint in-store, or worse, the date when the complaint got to the retailer's head office, or when it was received from the retailer by the manufacturer). All of these facts can put the state of the foreign body when it's received in the laboratory into perspective, and can help the analyst tremendously in being able to give a really accurate and helpful response.

Many types of foreign body turn up time and time again. A fragment of glass from the bottom corner of a jar is a case in point - these are often produced when someone is trying to scrape the last contents of a jar of jam or peanut butter using a spoon or knife, when a little excess pressure causes a small hole to be punched in the bottom corner of the jar. The fragments so produced have a very characteristic shape, but because the jar is empty, it is discarded without the consumer even being aware of the hole, and the glass fragment becomes associated with whatever food was being prepared that it fell onto, such as a slice of bread.

Another example of a recurring foreign body is a fragment of dental amalgam. These tend to be dark in colour and so are easily spotted. Curiously, white dental fillings are very rarely reported as foreign bodies - probably because they're much less easily seen! Dental fillings and tooth fragments are often associated with hard foods such as crusty bread or biscuits, or sticky foods such as toffee, and the source is almost always the complainant themselves!

Although historically microscopy has been, and continues to be, the cornerstone for foreign body analysis techniques, DNA analysis is beginning to become a useful tool in the armoury of the foreign body identifier - although it is still relatively expensive and cannot yet be offered as a "standard" technique. The main application is in identifying a fragment of animal or plant which cannot be identified by other means. It's less useful for identifying something of human origin, such as a hair. Human hair can usually be identified as such by its appearance under the microscope, and DNA can then sometimes be used to identify the person from whom it came. However, to do this you need comparison DNA samples from all the likely candidates, and apart from the cost of these multiple analyses, you generally need quite a good reason for asking someone for a sample of their DNA!

For a free fact sheet on foreign body analysis, send an e-mail to with the subject line: send contaminants