Food Safety : Mass Spectrometry, Flaws in Fermentation

by Food and Drug Administration (FDA)

(Page 2 of 3)

A Look at Mass Spectrometry

In other FDA food laboratories, chemists use mass spectrometry (MS) to do different types of analyses. MS enables chemists to identify organic chemicals such as dioxins, pesticides, and naturally occurring toxins. Combining the sophisticated technology of mass spectrometry with chromatographic techniques such as gas, super critical fluid, or high pressure liquid chromatography (see accompanying article), FDA chemists can identify and count chemical contaminants in food.

They do it by introducing a small amount of an extract of a food sample into a chromatograph, where chemical contaminants or pesticide residues are separated into individual compounds. (See diagram.) Then, in the mass spectrometer, an electronic beam bombards the separated chemicals, ionizing the molecules (giving them an electric charge) and fragmenting them.

The unique fragmentation pattern of individual ionized compounds allows the computer attached to the mass spectrometer to chart information about each and to identify the unknown chemical by comparing its spectrum, or "molecular fingerprint," to a known substance. The system also may allow chemists to accurately measure the amount of a chemical contaminant in a sample of food to parts per trillion levels and smaller.

FDA food chemists have developed laboratory procedures using MS to identify and count many kinds of food contaminants. For example, in an MS procedure using a technique called positive ion fast atom bombardment, chemists have characterized 12 of the neurotoxins in "red tide" — algae that bloom and produce toxins. These toxins can concentrate in fish and shellfish that feed on algae blooms. If eaten, the toxin-contaminated fish can cause serious illness and death. State authorities monitor waters and close the areas to fishing immediately when red tide appears.

FDA field laboratories around the country regularly apply MS and other laboratory procedures to identify and measure chemical contaminants in food. The Chicago district, for example, uses MS procedures to test milk and paper milk cartons for dioxin, a chemical contaminant that could migrate into milk from the paper containers.

FDA and other government agencies have used MS research results to make decisions about food problems. In a food-related crisis in 1989, for example, FDA chemists, working with food scientists from the Centers for Disease Control, needed to identify an unknown impurity in L-tryptophan, a widely used dietary supplement.

More than 1,500 persons who had taken the supplement had become ill and 39 died of eosinophilia-myalgia syndrome, a painful muscle and blood disorder. James Sphon, Ph.D., of FDA's Office of Physical Sciences, says that before starting the isolation and identification process, the mass spectrometrists had very little information about what the substance could be.

An FDA/CDC team developed a chromatographic procedure to show trace organic components in L-tryptophan. Using this procedure, along with epidemiologic data, FDA and researchers from medical centers and industry solved part of the mystery by identifying one impurity, 1,1'-ethylidene-bis-L-tryptophan (EBT), that could have been associated with the illness. Several other chemicals have been identified and through ongoing research, scientists will try to find out if these cause or contribute to eosinophilia-myalgia syndrome.

Flaws in Fermentation

FDA has also used mass spectrometry to measure the amount of ethyl carbamate (EC) in fermented products such as soy sauce, wines, or bakery products. EC, a chemical that sometimes forms as a byproduct of the fermentation process, is a suspected human carcinogen (cancer-causing agent).

The problem of carcinogens in fermented products got international attention in 1985 when Health and Welfare Canada reported that its scientists had detected EC in certain alcoholic products at levels that exceeded newly established Canadian guidelines. FDA and the U.S. Bureau of Alcohol, Tobacco, and Firearms (ATF) immediately began sampling wines and whiskeys from domestic and foreign producers to determine the levels of EC. (FDA and ATF share responsibility for regulating alcoholic beverages — FDA regulates their safety and cleanliness; ATF regulates the manufacture, composition specifications, labeling, and advertising.)

As with the Listeria situation, there was a problem of time spent in the laboratory searching for the presence of EC. Before a sample of distilled spirits could be run through the mass spectrometer, chemists had to "clean up" the sample in an unusually extensive, time-consuming procedure.

So William Brumley, Ph.D., formerly with FDA and now with the U.S. Environmental Protection Agency, developed a procedure using a more sophisticated mass spectrometer to shorten the analysis time. Brumley's procedure not only identifies and measures EC, it also does part of the sample cleanup.

In Brumley's approach, the MS analysis is carried a step further through an instrument called MS/MS. In this extended step, selected ions are collided with an inert gas. The impact breaks them into smaller, or "daughter," ions. This breakdown allows a more specific identification of the EC.

About the Author

www.fda.gov
FDA is A United States government body that oversees medical devices, including contact lenses, intraocular lenses, excimer lasers and eyedrops. In the US, these products must be approved by the FDA before they can be marketed.