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Food for Thought

SwRI chemists detect foreign materials, allergens and residues in food samples

By Lorraine G. Scheller

In recent years the news media have reported a number of food product recalls after consumption of these products resulted in illnesses and in some cases, deaths. The most publicized recalls were those attributed to bacterial contamination, such as E. coli in spinach and peppers and salmonella in peanuts and peanut butter. Other large recalls have involved chemical contaminants, most notably melamine, normally used in the manufacture of plastics. This compound was added to pet food and dairy products to make them appear higher in protein. Recalls have also been prompted by the presence of undeclared ingredients or allergens, banned dyes and pesticides, or higher than permitted levels of pesticide residues. Collectively, these recalls have resulted in heightened consumer concern over the safety of our food supply. This has prompted food suppliers to spend millions of dollars testing their products to assure consumers that the products are safe.

Southwest Research Institute (SwRI) chemists and scientists have provided many services to clients in food quality and safety, ranging across the food industry spectrum from the farm to the fork. They include farmers, distributors, manufacturers, wholesalers and retailers. Most projects are initiated to solve a specific concern. Examples have included evaluating flavor components through the determination of volatile organics; determining ethylene exposure of produce stored under a variety of conditions; analyzing volatile organic compounds to predict shelf life of milk and cereal products; kinetic studies to determine the effectiveness of bags in protecting produce from the effect of ethylene gas; determining the source of food contamination from the storage environment; investigating suspected intentional and unintentional food contamination; evaluating the effectiveness of common household washing and food preparation methods in reducing the levels of pesticide residues in produce; monitoring levels of potentially harmful compounds created in the production of food products; and determining the content of vitamins and other nutrients in foods.

Lorraine G. Scheller is manager of the Analytical and Environmental Chemistry Department of SwRIŐs Chemistry and Chemical Engineering Division. She has extensive experience in the extraction and analysis of environmental and biological samples and has conducted studies under U.S. Environmental Protection Agency, Food and Drug Administration and Good Laboratory Practice guidelines for more than 15 years. She is responsible for groups that perform organic analyses using high performance liquid chromatography, capillary electrophoresis, gel permeation chromatography and gas chromatography.

Food can be a single commodity such as fruits and vegetables, or it can be very complex as are most processed foods. This presents many challenges to those who perform chemical analyses. Keys to the success of these analyses include sophisticated sample preparation and analytical techniques that aim to reduce interferences caused by natural and artificial colors, sugars, starches and preservatives. Due to the shelf life constraints of most foods, these analyses must be performed in a short period. Turnaround of data to the client typically ranges from a few hours to a few days from the time samples are received in the lab.

Over the past 20 years, food chemists and scientists at SwRI have analyzed more than 40,000 produce samples for approximately 150 pesticide residues. During that time, the food chemistry laboratory has had to stay abreast of changes in regulations and tolerances for specific compounds and commodities. Additionally, many compounds have been banned and newer pesticides put into use. The SwRI team has adapted its analyses in response to these changes and maintains a same-day turnaround for samples received at the lab. This constraint has pushed the lab to improve upon standard sample preparation and evaluation techniques.

New techniques

The SwRI lab has implemented dispersive solid-phase extraction techniques, which allow for sample extraction and interferent cleanup in fewer steps, using less solvent, to analyze samples more quickly while reducing laboratory costs and waste. Other improvements in food chemical analyses have included implementation of mass spectroscopy (MS) to the detection of targeted compounds. Typical screening methods formerly utilized gas chromatography (GC) coupled with electron capture detection (ECD), nitrogen phosphorus detection (NPD), flame photometric detection (FPD), flame ionization detection (FID) or liquid chromatography (LC) coupled with ultraviolet detection (UV) and/or fluorescence detection. A positive detection by either GC or LC required confirmation using a dissimilar technique to positively report a finding. The use of GC/MS or LC tandem MS (LC/MS/MS) provides detection, identification and confirmation of the compound in a single run. This allows for more timely reporting of data to clients.

The SwRI lab uses solid-phase extraction techniques that allow for sample extraction and interferent cleanup in fewer steps and with shorter turnaround times.

The chemical analytical labs have also responded to emerging food issues, such as the discovery of a potential cancer-causing compound, acrylamide, in baked and fried foods. In 2002, a group of Swedish scientists unexpectedly detected acrylamide in many baked, fried and roasted foods. This was alarming because acrylamide is a suspected carcinogen, and the levels that the scientists found in these foods far exceeded limits set for public drinking water supplies. Interestingly, the scientists noted that acrylamide was rarely seen in boiled or raw foods.

Food regulatory agencies worldwide searched for the cause of this phenomenon. It was later shown that acrylamide was actually being produced during the cooking process through a chemical reaction, known as the Maillard reaction, which occurs when foods are browned. Essentially, the reaction takes place when an amino acid and a reducing sugar are exposed to high temperatures. Acrylamide was being formed through a reaction between the amino acid asparagine, which is naturally present in many starchy foods, and glucose or fructose as the reducing sugar.

Chemical analysis of food samples begins with the use of household blenders to reduce foods to fine particles whose chemical components can be extracted for quick and consistent screening and analysis

Some common food preparation practices can result in conversion of the naturally occurring amino acid asparagine into acrylamide, a potential cancer-causing compound, when heated to high temperatures in the presence of certain sugars.

Food manufacturers concerned with the levels of acrylamide in their products contracted the SwRI food laboratory chemists to monitor the levels of acrylamide in their products, along with the levels of the amino acids and sugars that combine to produce it. The lab, in turn, streamlined its standard sample preparation techniques to provide faster throughput to accommodate the simultaneous demands of greater volume and shorter turnaround times. The lab incorporated extraction and cleanup procedures that require fewer steps. The result was a "cleaner" sample extract, which aids in identifying the compound and also reduces the time needed for analytical instrument maintenance. Once processed, the samples are analyzed using GC/MS or LC/MS/MS techniques. The lab today processes from several hundred to several thousand samples per week, and it reports analysis data to clients within days of receiving the sample.

Ensuring safety of globally sourced foods

Imported foods continue to be a concern as the U.S. food supply becomes more global. In 2007, the media reported widely on pet food products that sickened thousands of cats and dogs. It was determined that wheat gluten imported from China had been adulterated with the industrial chemical melamine, which standard testing methods can misinterpret to indicate artificially high protein content. The next year, in 2008, hundreds of Chinese infants were sickened when melamine was added to infant formula in that country. In response to concerns over the safety of imported foods, the SwRI food chemists were contracted to test a wide range of imported products for melamine and cyromazine, a compound which is a metabolite of melamine. The SwRI team developed several analytical methods for these compounds, including a simple screening run using LC for samples that were not expected to contain the target compounds. Meanwhile, GC/MS and LC/MS/MS analyses were run on products with a tentative positive detection using LC, as well as products about which not much was known, to provide a simultaneous identification and confirmation. One or both of the chemicals were found in several products, but at relatively low levels. The levels detected did not indicate an intentional adulteration of the product.

Small samples can be screened rapidly and in high numbers using new mass spectroscopy processes to detect targeted compounds.

Products and packaging

The SwRI labs have also responded to requests to investigate packaging and shipping conditions and their effects on food products during transport. Plastics are typically manufactured with flame- retardant additives. One new type of high-density polyethylene plastic shipping pallet is manufactured using the additive Deca, a type of brominated flame retardant. The SwRI chemists performed experiments to investigate whether a specific Deca component, brominated diphenyl ether (BDE) congeners, can migrate from the plastic pallet onto the shrink-wrap of the packages loaded onto it. Results demonstrated that BDE congeners could leach from the plastic pallet to the shrink-wrap beneath the product packages.

The food chemistry laboratories at SwRI are staying abreast of other food safety issues as they arise. Recent concerns involve the presence of bisphenol A in plastic bottles, phthalates in plastic food storage and packaging, banned colors in imported products, undeclared allergens in products and counterfeit products. The SwRI team remains dedicated to providing accurate and timely analyses tailored to fit clients specific needs.

Although there is much concern over the presence of chemical contaminants in a variety of foods, it must be noted that recent advances in technology allow analytical chemists to detect these compounds at ultra-low levels, typically at the parts-per-trillion level. However, at what levels these compounds cause harm to the human body is not always known. Therefore, the responsibility of setting limits for these compounds in food falls to the government agencies that oversee the food industry.

In response to food-safety concerns, SwRI chemists developed analytical methods to screen food samples for the industrial chemical melamine and for cyromazine, a metabolite of melamine.

Questions about this article? Contact Scheller at (210)-522-2182 or


Sundlof, Stephen F. "Foodborne illness outbreak associated with salmonella." 11 Feb. 2009. U.S. Department of Health and Human Services. 29 June 2009.

Stadler, Richard H., Imre Blank, Natalia Vargas, Fabien Robert, Jorg Hau, Phillippe A. Guy, Marie-Claude Robert, and Sonja Riediker. "Food chemistry: Acrylamide from Maillard reaction products." Nature 419 (2002): 449-450. Nature. 3 Oct. 2002. 13 Jan. 2009.

Raloff, Janet. "Pesticide may seed American infant formulas with melamine." ScienceNews 3 June 2009. Society for Science and the Public. 29 June 2009

Published in the Winter 2009 issue of Technology Today®, published by Southwest Research Institute. For more information, contact Joe Fohn.

Winter 2009 Technology Today
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