Recent scandals involving adulteration of critical food products with dire health consequences need look no further than the addition of melamine to infant milk powder. The protein content of a variety of dairy foods, sweets and pet food was being boosted falsely and illegally by the addition of melamine. It is a dangerous material. It had been tried as a non-protein nitrogen source for cattle feed until this was abandoned for safety reasons (Newton and Utley, 1978). Dry powder infant formula was one of the main targets by unscrupulous suppliers and in 2008 there were six reported deaths of babies and at least 30,000 hospitalizations (Chan et al., 2008; WHO, 2008). The health issue was attributed to crystal formation in the kidneys similar to stones and producing renal failure.

Melamine continues to emerge in foodstuffs and both suppliers and buyers need to remain vigilant to its presence. A safety limit of melamine ingestion has been officially set at 2.5ppm for adult foods and at 1 ppm for infant products by the US Food and Drug Administration (FDA). The maximum residue level of melamine in infant formula is legally regulated at 1 ppm by Chinese government after the adulteration was observed (Guo et al., 2010).

Melamine (2,4,6-triamino-1,3,5-triazine)  is a compound with a high nitrogen content of 67% because it has three attached amino groups. Conventional nitrogen content testing relied on the Kjeldahl or Dumas methods which meant small additions of melamine could be used to bolster levels illegally.  It was readily available as it is industrially used to produce melamine-formaldehyde resins which are turned into plastics and coatings. It also serves as a fire suppressing material. It hydrolyses to ammeline, ammelide and cyanuric acid under strong acid or alkaline conditions. Following the scandal, a number of analytical methods were rushed out to meet the demand for rapid analysis.

Current separation and detection methods can use chromatography with a variety of detectors and mass spectroscopy is most frequently adopted. High performance liquid chromatography (HPLC) (Zhong et al., 2011), liquid chromatography with mass spectroscopy (LC-MS) (Goscinny et al., 2011), gas chromatography with mass spectroscopy (Miao et al., 2010) have all been successfully applied. There are many more variants on these methods which is outside the scope of this post article.  Specific detection methods such as near-Infrared (NIR) and mid-Infrared (FTIR) have also been examined with success (Balabin and Smirnov, 2011). The NIR detection method can be applied in an assay time of 1 minute and can detect levels as low as 1 ppm melamine.  Such methods are relatively quick with good precision and sensitivity.

Recently, Raman spectroscopy has been attempted because it can handle complex compositions and single out specific molecules which other detectors are incapable of sorting out. It is not generally used for trace material detection but can be coupled to immunological separation. A recent method exploits Raman spectroscopy’s ability to be surface enhanced and so be capable of detecting trace contents of melamine (Li et al., 2015). The detection limit is as low as 0.79 x  10^–3 mmol/L and analysis can be completed in 20 minutes.

References

Balabin, R. M., & Smirnov, S. V. (2011). Melamine detection by mid-and near-infrared (MIR/NIR) spectroscopy: a quick and sensitive method for dairy products analysis including liquid milk, infant formula, and milk powder. Talanta, 85(1), pp. 562-568.

Chan, E., Griffiths, S., Chan, C. (2008) Public-health risks of melamine in milk products. Lancet 372 pp. 1444–5

Goscinny, S., Hanot, V., Halbardier, J. F., Michelet, J. Y., & Van Loco, J. (2011). Rapid analysis of melamine residue in milk, milk products, bakery goods and flour by ultra-performance liquid chromatography/tandem mass spectrometry: From food crisis to accreditation. Food Control, 22, pp. 226–230.

Guo, L. Q., Zhong, J. H., Wu, J. M., Fu, F. F., Chen, G. N., Zheng, X. Y., et al. (2010). Visual detection of melamine in milk products by label-free gold nanoparticles. Talanta, 82, pp. 1654 -1658.

Lam, C. W., Lan, L., Che, X. Y., Tam, S., Wong, S. S. Y., Chen, Y., et al. (2009). Diagnosis and spectrum of melamine-related renal disease: Plausible mechanism of stone formation in humans. Clinica Chimica Acta, 402, pp. 150–155.

Li, X., Feng, S., Hu, Y., Sheng, W., Zhang, Y., Yuan, S., Zeng, H., Wang, S. and Lu, X. (2015), Rapid Detection of Melamine in Milk Using Immunological Separation and Surface Enhanced Raman Spectroscopy. J. Food Sci., 80: C1196–C1201. doi: 10.1111/1750-3841.12876

Lin, M., He, L., Awika, J., Yang, L., Ledoux, D., Li, Ha., Mustapha, A. (2008) Detection of melamine in gluten, chicken feed, and processed foods using surface enhanced Raman spectroscopy and HPLC. J Food Sci 73: T129–T34.

Mauer, L. J., Chernyshova, A. A., Hiatt, A., Deering, A., & Davis, R. (2009). Melamine detection in infant formula powder using near-and mid-infrared spectroscopy. J. Agric. Food Chem., 57(10), pp. 3974-3980.

Miao, H., Fan, S., Zhou, P. P., Zhang, L., Zhao, Y. F., & Wu, Y. N. (2010). Determination of melamine and its analogues in egg by gas chromatography–tandem mass spectrometry using an isotope dilution technique. Food Additives and Contaminants: Part A, 27, pp. 1497–1506.

Newton, G.L. and  Utley, P.R. (1978)  Melamine as a dietary nitrogen source for ruminants, J. Anim. Sci. 47  pp. 1338–1344.

World Health Organization (WHO) (2008) Melamine contamination event. http://www.who.int/foodsafety/fs management/infosan events/en/index.html.

Zhong, Y. B., Zhang, L. J., Zhang, H. C., Liu, J. X., & Wang, J. P. (2011). Immunoaffinity based solid phase extraction for the determination of melamine in animal derived foods followed by LC. Chromatographia, 73, pp. 1211–1215.