International Community Responds to Melamine Scare

The increasing number of contaminants producers are required to test for puts a heavy burden on the food industry. Government agencies in each country define different allowed levels and testing methods for these contaminants, thus requiring food producers to keep track of a large number of regulations and maintain a wide array of testing capabilities to satisfy the testing requirements for each geographic area. While some regions such as Europe set performance requirements for testing methods, others develop fully described analysis methods that must be followed. Each type of food may require a different testing regime and may have different allowed levels for the same contaminant.

A wide variety of testing methods can detect melamine, but their use varies by country. An enzyme-linked immunosorbent assay is commercially available to determine quantitative levels of melamine. High performance liquid chromatography (HPLC) can also be used in conjunction with ultraviolet (UV) detection for melamine screening. Gas chromatography (GC) or HPLC can be combined with mass spectrometry (MS) to provide more accurate screening. Also, adding a second mass analyzer (GC-MS-MS; LC-MS-MS) can provide very reliable, selective, and sensitive methods for melamine detection and quantification in a wide variety of food products.

With such a wide choice of available methodologies and instrumentation available for detection of a wide range of substances, multiple test methods are developed and used globally to monitor for contaminants such as melamine. For example, the Chinese government’s General Administration of Quality Supervision, Inspection, and Quarantine has developed a method for testing milk based on LC-MS-MS, while the FDA has published a different method based on the same instrument platform. The use of multiple methods can complicate interpretation of results and their use to assure MRL compliance. Efforts to produce one single set of methods for each technology platform and each contaminant, globally, for a particular food type (e.g. milk), could lessen confusion over interpretation of results, reduce testing times, and lower production costs.

Hyphenated Systems

By far the most common technology platforms used by laboratories around the world for detecting chemical food contaminants such as melamine are “hyphenated” systems that combine chromatography with mass spectrometry. The first method for detecting melamine in food matrices, which used GC-MS, was developed in 2007 to detect contamination in pet food. This method is suitable for both screening and quantification, although at a higher limit of quantification (LOQ) than GC-MS-MS due to a slightly lower selectivity. Derivatization of the sample is necessary prior to injection into the system, but some GC-MS methods with back flushing can produce results less than 15 minutes after injection.

Melamine can also be detected with LC-MS methods. While the limit of detection (LOD) is significantly lower than that of the GC-MS method, the LOQ is still relatively high. Solid phase extraction is required during sample preparation in order to increase selectivity. A UV detector can also be used in place of MS, with an LOD comparable to GC-MS. While original HPLC methods for confirmation utilized a reversed-phase ion-pair approach, simple and robust methods that use ion exchange chromatography are now available. These methods produce results in less than 10 minutes.

Standard methods are available for all of these technology platforms; most testing laboratories will have at least one of them. Some instrument suppliers provide all of these platforms and have expertise in their applications, including melamine testing. When a food safety issue arises, most testing laboratories can develop or adopt new testing methods in a matter of days.

Food testing, however, could also benefit from even more selective methods. The Kjeldahl method, routinely used to determine total protein in foods, is very nonselective; it simply determines the total amount of nitrogen present in the food sample. Widespread adoption of a more selective test might eliminate the adulteration of food with melamine. In fact, the World Health Organization (WHO) has recommended the development of more specific, rapid, and low-cost methods for protein analysis that do not include non-protein nitrogen to monitor for adulteration with sources of non-protein nitrogen, including melamine.