Between 2013 and 2015, an estimated 9.2 billion pounds of milk powders (MPs) were created. This enormous amount highlights the significance of these products in the general population’s diet as they include vital nitrogen-rich proteins.
To pass quality assurance (QA) testing, certain organizations add compounds to these products which have a high nitrogen content. This fraudulent process enables companies to increase their profits by adding proteins that are less nitrogen-rich to the products. This procedure can have dangerous consequences. Melamine was added to MP in 2008, which resulted in the ill-health of 300,000 people and the death of six babies.
As only specific compounds were screened at this time, these MPs were able to pass QA because melamine was an unknown adulterant. The food safety industry has since moved towards non-targeted techniques to identify unknown and known adulterants.
This perspective employs chemometric techniques, for example, Raman and infra-red (NIR) spectroscopy, to analyze several authentic samples and produce a reference set.
The variance is then determined, and confidence limits are calculated to enable unknown samples to be categorized as non-conforming or authentic. Even slight variations between data points can provide the detection of adulterants using conformity index (CI) analysis.
A proof of concept study has recently demonstrated that solution-state 1H NMR spectroscopy in combination with CI analysis can provide the non-targeted detection of multiple MP adulterants. This method also has the advantages of a high sample throughput, high sensitivity, and minimal sample preparation.
Authentic MP samples from 46 international sources were tested to generate a reference set utilizing a Bruker Avance III 600 MHz spectrometer. The variance in the data was determined through CI analysis and a maximum CI (MaxCI) limit of ≥7.38 was established. A variety of adulterants were then investigated and any samples with a MaxCI ≥7.38 were categorized as non-conforming.
This technique had a high sensitivity to the small, nitrogen-rich organic molecules dicyandiamide (DCD) and melamine, which are harmful to human health. Each of these compounds features peaks in regions that are unobstructed by MP signals (5.95 ppm and 6.58 ppm, respectively), which allow concentrations of 0.005% w/w and 0.05% w/w, respectively, to be identified.
Adulterants that do not present a considerable risk to health were also evaluated. Maltodextrin and sucrose also contain signals in regions that lack MP metabolite peaks (5.16 ppm and 5.46–5.47 ppm, respectively) and could be detected at concentrations as small as 0.5% w/w.
Ammonium sulfate (5% w/w) and urea (0.5% w/w) were also identified, but the technique was less sensitive because these adulterants contained no peaks in unhindered regions. While protein adulterants were investigated, they could not be detected because of their poor solubility in DMSO.
Compared to non-targeted techniques combined with Raman and NIR, the sensitivity achieved when detecting the dangerous adulterant melamine is much higher, showing that this method has great promise in the QA of MPs.
References and further reading
- Bergana MM., et al. (2019). Non-Targeted Detection of Milk Powder Adulteration by 1H-NMR Spectroscopy and Conformity Index Analysis. Journal of Food Composition and Analysis. https://doi.org/10.1016/j.jfca.2019.01.016.
- http://www.bbc.co.uk. (2010). China Dairy Products Found Tainted with Melamine. https://www.bbc.co.uk/news/10565838
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