Adulteration of milk products and pet food with melamine underscores weaknesses of traditional methods, experts say

The paper, now available online, is authored by a team of experts led by Jeffrey Moore, Ph.D., of the U.S. Pharmacopeial Convention (USP). USP publishes the Food Chemicals Codex (FCC), a compendium of quality standards for food ingredients.

The paper examines how reliance on 19th century methods -- primarily the Kjeldahl method and the combustion (Dumas) method -- for measuring total protein content in foods and the lack of more specific methods allowed for the adulteration of protein-based foods with melamine and related nonprotein compounds in 2007 and 2008. Rather than quantifying protein content, these methods rely on total nitrogen determination as a marker to estimate the amount of protein in a food -- and are the current standard for the food industry. Such approaches may allow unscrupulous parties to fool these tests simply by adding a cheap organic compound containing nitrogen, which can result in severe physical damage to humans and animals as well as financial consequences for food producers and consumers through price increases, market disruptions, trade restrictions, product liability costs, loss of revenues and brand damages.

"While the globalization of the food industry has provided consumers with a seemingly endless number of choices and year-round availability to enhance their diets, the events of 2007 and 2008 have shown that it may also introduce new risks -- leaving the industry as a whole and individual consumers vulnerable to potential serious consequences," said Dr. Moore. "Adulteration of foods represents a significant public health threat that needs to be addressed. In this paper, we look at a path forward on the complex issue of protein measurement -- development, validation and implementation of new analysis methods specific for protein-based food ingredients."

As described in the paper, protein content is held at a premium because of the nutritional value of proteins as well as their contribution to functional properties of food such as texture and flavor. Thus, protein quantification is an important tool used throughout the global food supply chain, helping to determine the economic value of a food. The authors note that as long as the value of food ingredients is based on protein content, the incentive to adulterate these materials by measures designed to inflate protein measurement will exist -- necessitating the need for new approaches used by the food industry.

To stimulate discussion and to provide new information about the development and adoption of new or alternative protein methodologies, the authors of the paper review the following:

• the early history of food protein methodology
• analytical strategies to prevent intentional adulteration of foods and food ingredients
• challenges of developing or adopting new or alternative protein quantification methods and associated reference materials
• criteria against which new methodologies can be evaluated, and
• emerging methodologies for total food protein measurement, including pros and cons.

The paper looks at the two primary analytical strategies to prevent "economic adulteration of food," which is defined as "fraudulent addition of non-authentic substances or removal or replacement of authentic substances without the purchaser's knowledge for economic gain of the seller." The first approach uses analytical tests to identify one or more suspected adulterants, where an "absence of" result indicates the test material is not adulterated with a specific material. This requires prior knowledge about the adulterant and therefore is not useful for detecting unknown adulterants, thus prohibiting it from preventing future adulteration with unknown substitutes. The second approach is based on compendial identification and purity tests that substantiate an ingredient's identify and quantify its purity, i.e., a "presence of" result. This approach is effective when either a known or unknown adulterant is substituted for the original material at concentrations high enough to be recognized in test results. As noted in the paper, it is less useful when adulterants are present in low concentrations; however, from a practical perspective, counterfeiters often must adulterate at relatively high concentration levels to realize economic gain. Such purity standards are contained in compendia including the FCC. At this time, no current compendial methods are sufficiently selective to differentiate protein from other nitrogen-containing compounds.

The paper identifies a host of existing methods for food protein measurement that may exhibit potential for broader use (and the associated pros and cons of each method), including infrared methods, amino acid-based methods and new spectral probes. Certain methods have existed for some time but have not achieved routine use by the food industry, instead having been largely limited to research applications. However, the authors note that even though these methods may have some utility, many food matrices have unique requirements that necessitate different approaches for protein measurement. This may require a combination of different protein analysis methods to effectively prevent adulteration. The paper also looks at emerging methods including antibody based methods and high performance liquid chromatography (HPLC) that may be useful once sufficiently developed for practical use in routine protein measurements.

"Through further exploration of available and emerging methods -- and new work in this area -- the ultimate hope is to protect public health by preventing the next melamine," noted Dr. Moore.