Investigating black specks in a food product

A US food manufacturer needed our analytical support to help them navigate a potentially damaging physical contamination issue. Here's how we helped.



During routine Quality Control (QC) checks, our client discovered black specks in their food product. The defect was present in multiple batches and across a large volume of finished product. This was causing major disruption for production and the overall supply chain, so needed to be urgently resolved to prevent a potentially significant financial loss for the company.


RSSL was asked to carry out a thorough investigation to identify the precise nature of the physical contaminant, confirm the root cause and help the client take the right course of action.   



Figure 1: Black specks in cheese



Figure 2: Excised black speck



Our approach


Leveraging our broad capabilities in physical contamination identification and physical characterisation, we carried out a series of analytical tests to provide the answers our client needed.


Our experienced food microscopists began by identifying and excising the black specks from the affected product sample. Using light microscopy, we were able to determine the size, shape and characteristics of the foreign material. Initial findings revealed that it was soft and somewhat pliable, not brittle or hard. But we needed to know more.



We used Fourier transform infra-red (FT-IR) spectroscopy to examine a subsample of the black fragment. The resulting spectrum showed that the sample correlated with a library Ethylene Propylene Diene Monomer (EPDM).  Otherwise known as a common type of rubber.


This was confirmed by a further test. X-ray microanalysis found that the sample contained a high level of carbon with oxygen, magnesium, silicon, sulphur and calcium also present. This was consistent with a polymeric material with fillers.


Figure 3: FT-IR spectrum of the sample material (red) compared with a library ethylene propylene diene monomer spectrum (blue).


Figure 4: X-Ray Micrograph of black sample. 


These findings led the client to suspect that the black speck contamination was caused by the breakdown of some rubber seals in the food production line. Given the large number of possible sources, they needed to determine the exact location of the problem seal and asked us to extend our investigation.

Working with small sections taken from variety of seals used in the factory, we carried out additional analysis to find a match with the black fragments found in the food. Again, our systematic approach ensured the results would be accurate and reliable.



Figure 5: Examples of seals examined (One to four)




Using FT-IR analysis on all four samples, we produced corresponding spectra and compared them against the original. One seal (seal 4) clearly stood out as the closest match, with a correlation in the fingerprint region of the spectrum (1200 to 1600cm-1). We then used SEM analysis to compare the microscopic surfaces of the samples. The resulting electron images matched the same seal (seal 4) to the black speck fragments – further corroborating our findings.



Figure 6: Backscattered electron image of seals one to four in figure 6


The outcome


Based on our robust analysis, the client was able to confidently inspect and remove the damaged seals from the identified production area and clean downstream. This decisive action meant they no longer experienced black specks in their products and disposed of all contaminated batches before they entered the supply chain.



RSSL played a pivotal role in this investigation. The experienced team gave us the technical support we needed to understand exactly what we were dealing with and successfully resolve a potentially damaging food contamination issue.

US Food Manufacturer




How RSSL can support with physical contamination investigations

RSSL is widely acknowledged as a world leader in foreign body identification. Our microscopy team have over 100 years of expertise, and have built up a database containing thousands of reference samples, which supports our work in analysing new incidents. We use highly sophisticated microscopy and spectroscopic techniques to identify physical contaminants and can provide rapid turnaround via our Emergency Response Service. We provide guidance on how to send samples for testing, and also advise on preventing foreign body incidents, as well as offering a pre-screening service that is useful for identifying sources of metal swarf should these arise in factory equipment. To find out more click below or complete the contact form.

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