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From: Food Quality & Safety magazine, February/March 2009

The Great Melamine Scare

The scandal draws attention to standards and leads to development of new tests

by Denise Ibens

The recent crisis involving Chinese milk adulterated with melamine once again brings food safety into the public spotlight. The problem has quickly become an international one, with melamine detected in U.S.-produced baby formula, as well as in chocolates distributed in Canada, biscuits marketed in the Netherlands, condensed milk manufactured in Thailand, and eggs sold in Hong Kong. Chinese dairy exports have declined more than 90% since the contamination became public.

The international community responded strongly to the crisis; the U.S. Food and Drug Administration (FDA) even took the unusual step of blocking the importation of an entire category of one country’s foods: Chinese products containing milk. The FDA has also found baby formula produced in the United States to be safe after establishing a maximum residue limit (MRL) of 1 part per million (PPM) and testing more than 70 products. The European Commission also banned the import of Chinese milk and milk products into the European Union (EU), including all products for infants and young children containing any milk of Chinese origin.

The effects of such bans on the food production industry are multiple, profound, and far-reaching. A producer that depends on a banned imported foodstuff not only suffers economic loss to the impacted product but also faces lost sales caused by loss of public confidence. The resulting brand damage can be devastating, and recovery can require significant time and expense when consumers have moved on to other suppliers’ products.

This most recent crisis underscores the need for increased food safety vigilance. Fraudulent adulteration of food products should be dealt with rigorously, with stringent penalties for offenders. Efforts to harmonize global testing methods and limits for allowable contaminant levels must also continue, while response to potential safety threats can be improved by the adoption of methods, systems, and regulations that enable the tracking of a foodstuff from farm to fork. Finally, a more selective sample preparation and testing technology is needed to enable rapid screening of food contaminants.

Food Fraud

Food safety monitoring systems are in place worldwide to detect and prevent human exposure to food residues and contaminants. However, the melamine crisis highlights a more sinister threat to food quality and safety: fraudulent food adulteration.

Melamine was intentionally added to milk in China for one purpose only—to artificially increase the measured protein content of the milk. The Kjeldahl assay, which determines the total nitrogen in a sample, is the test most widely used to determine the total amount of protein in foods. Because every molecule of melamine contains six atoms of nitrogen, adding a small amount of melamine to milk significantly increases the amount of nitrogen detected in the test, resulting in erroneously high protein estimates. Often, the melamine used for this purpose also contains cyanuric acid, an analog that complexes with melamine to form crystals that accumulate in the kidneys, frequently leading to kidney stones and renal failure.

The Chinese melamine incident was a case of intentional, greed-induced fraud perpetrated by people with knowledge of testing methods. Intentional misrepresentation of food also occurs; recently, fish were mislabeled as more expensive varieties in New York fish markets and restaurants, a deception discovered by researchers using DNA testing. The damage inflicted by such perpetrators is incalculable, and it exacts a high cost in shaken public confidence in the global food production system. Constant international vigilance, appropriate criminal penalties, and globally coordinated efforts to enforce those penalties should be considered to assure the future safety of the food production system.

Global Methods Harmonization

The milk adulteration incident points out the need for a continued effort to generate a single, globally harmonized set of MRLs, as well as testing methods for food residues and contaminants. For example, China and the FDA have now set an allowable limit for melamine of 1 mg/kg (1 PPM) for infant baby formula and 2.5 PPM for other products, while the European Commission has set a limit of 2.5 PPM in all milk-containing products and a tolerable daily intake of melamine of 0.5 mg/kg body weight.

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.

The use of multiple methods can complicate both the interpretation of results and their use to assure compliance to MRL regulations. Efforts to produce one global set of methods for each technology platform and each contaminant for a particular food type could lessen confusion over results interpretation, reduce testing times, and lower production costs.

Food Traceability

Ultimately, assuring the safety of food requires tracking it from the farm through the processing plant to the consumer. In the EU, documentation is required to identify the suppliers of food, feed, food-producing animals, and ingredients in products, as well as the businesses to which products have been supplied. In the United States, the new country of origin law identifies the country from which the food is being imported.

Several other countries, including Japan and Canada, also have fairly high traceability requirements, and organizations such as the Codex Alimentarius Commission of the WHO are developing recommendations for traceability in the food industry. In addition, firms across the U.S. food industry are now adopting their own traceability systems in order to improve production and distribution efficiency, differentiate their products, and monitor and control food safety. Benefits of adoption include lower cost distribution, reduced recall expense, and the ability to charge higher prices for products with documented origin.

No matter which tracking system a company adopts, it is vital that the system provide the appropriate level of breadth, depth, and precision. A tracking system that compiles information on all of a food’s attributes would be prohibitively expensive, so the critical parameters must be identified. In order to assure food safety, the depth of the system (how far back it can track a product) is dependent on those points where hazards can occur and remedies can be applied. The required precision with which the system can track a food product can also vary. For example, while it is necessary to track meat back to a specific cow in order to rule out mad cow disease, it may not be necessary to track wheat beyond the grain elevator.

As the ability of the food industry to trace a food’s path through the production system improves and expands, efforts to globally harmonize standards, regulations, and tracking systems should continue. This will assure the ability to quickly identify a food safety issue, track it to its source anywhere in the world, and take timely steps to prevent or limit any health threat.

Ultimately, assuring food safety requires highly sensitive, selective, and reproducible methods for monitoring a wide variety of foods for contamination. The challenge is made greater by the reality that foods are very complex matrices, necessitating a wide range of sample preparation methods that are often time-consuming and costly, and which must be applied before analysis can begin. In order to adapt to new threats, rapid development of simple, fast, and reliable sample preparation methods and assays for new substances of interest, based on technologies already used in testing laboratories, is necessary.

As industry’s ability to trace foods path through the production system improves and expands, efforts to globally harmonize standards, regulations, and tracking systems should continue.

Denise Ibens is a food industry marketing manager for Agilent Technologies. Reach her at or (302) 633-8534.



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