Demand grows for GMO testing
By Ken Roseboro, Contributing Editor
Contents
ELISA: fast and inexpensive
PCR: sensitive and precise quantification
Standards are needed
New technologies
Demand for non-GMO now driving market, but experts see greatest potential in testing for new GM output traits. This feature is the second in a three-part series examining the potential for GM foods, testing and the future of biotechnology in foods.
The debate over genetically modified crops and food products has spawned a new industry: GMO testing. Over a dozen U.S. labs now offer GMO testing services, and several companies manufacture and sell GMO test kits. According to industry estimates, the total market for genetic testing may exceed $10 million in 2000, and double in the next three to five years as new GM crops are introduced.
The three most common methods used to detect GMOs are herbicide bioassay, a simple test used to detect herbicide-resistant GM crops; enzyme linked immunosorbant assay (ELISA); and polymerase chain reaction (PCR). Of the three, ELISA and PCR are most common GMO test methods used in the grain and food industries.
ELISA: fast and inexpensive
ELISA methods use antibodies to detect specific proteins produced by genetically modified DNA "events" in soybeans, corn, canola, and cotton. The test uses a standard 96-microwell ELISA plate with antibodies coated on the insides of each microwell. A sample is ground and the protein is extracted and added to the microwells. If the targeted protein is present, it binds to the inside of the wells. The protein is then "sandwiched" by another antibody that has an enzyme attached to it. A color substrate is added that reacts to the enzyme creating a color change. The intensity of color indicates the amount of the protein present. The test can take two to four hours.
Another version of the test uses lateral flow strips and delivers results in two to five minutes. The strip tests are commonly used at grain elevators where a fast, "yes or no" answer is needed.
ELISA tests are specific to each GM event. Kit manufacturers, Envirologix and Strategic Diagnostics, sell both plate and strip tests for a range of genetic events, including the now famous StarLink Cry9C.
The main advantages to ELISA tests are speed, user friendliness, and low cost. Limits of detection vary among the tests, according to Dean Layton, VP of marketing at Envirologix. The company's Cry9C plate test can detect the GM protein down to 0.01%, while the strip tests can detect at 0.25%.
ELISA tests work best on raw grains, but are limited in detecting proteins in processed foods because heat processes will denature the proteins, making detection difficult.
PCR: sensitive and precise quantification
PCR is considered the most sensitive and precise GMO test method because it allows direct analysis of the DNA. PCR is analogous to a word search on a computer; it uses biochemical processes to scan through a sample of DNA and locate genetically modified DNA sequences.
The keys to the search are primer sets, which are short pieces of DNA that recognize modified DNA sequences. A primer set identifies the beginning and end of the targeted sequence. When a sequence is located, the PCR equipment multiplies the targeted gene billions of times until it can be measured precisely. Thus, PCR can detect the presence of GM gene sequences even when they are present at very low levels.
Real-time PCR is a second-generation technology that provides precise quantification over a wide range of GMO concentrations. Real-time uses fluorescent probes to detect and quantify GMOs and operates in a closed system to reduce the chance for cross contamination and human error.
According to John Fagan, chief scientific officer at Genetic ID, a GMO testing lab, there are challenges to detecting GM material in processed foods.
"Food processing can fragment the DNA, which can reduce the sensitivity of the analysis," says Fagan. "You must isolate the DNA so that it is free of inhibitors, minimize DNA degradation, and obtain a high enough yield of DNA to perform an effective analysis."
To overcome these challenges, Genetic ID customizes DNA extraction and purification procedures for each processed food it analyzes.
PCR can quantify GM content in a sample to 0.01%, and provides greater flexibility than ELISA tests, which are specific for one transgenic trait. However, a PCR analysis require more time, two to three days and costs more, between $100 to $300 per sample.
Standards are needed
One of the problems facing the GMO testing industry is a lack of uniform standards among the different methods. For example, PCR labs will use different protocols for sample preparation, DNA extraction, PCR amplification, and electrophoretic analysis of PCR reaction products. This lack of uniformity often leads to inconsistent results arising between labs. To address this problem, the American Association of Cereal Chemists is working with the USDA's Grain Inspection Packers and Stockyard Administration, the National Institute of Standards and Technology (NIST), and Europe's Institute of Reference Materials and Measurements (IRMM) to establish analytical standards for both ELISA and PCR tests.
Establishing uniform standards is critical. "The testing industry can't survive unless there is a standard to calibrate testing methods to," says Dwight Denham, global business unit director at Strategic Diagnostics, Inc.
New technologies
Industry experts, such as Denham and Fagan, recognize the primary limitation of the present methods: Lack of versatility. Each test must be created to look for a specific GMO. Currently, no simple test exists that can universally test for genetic modification.
Efforts to create more universal methods are, however, underway. Europe-based Genescan has developed a "biochip," which is a micro array with hundreds of microscopic wells, each containing primer sets. PCR is used to amplify DNA, and the material is put on the biochip. A fluorescent reader detects positive or negative events in the wells. Hundreds of GMO events can be detected using the biochip. Qualicon, a Dupont subsidiary, recently introduced its Bax System PCR Assay, a qualitative PCR test kit, designed to help food processors perform in-house threshold testing on raw and processed corn and soy products. Genethera, a lab in Denver, CO, is developing a Real-time PCR method using robotics to streamline the testing process. Fagan says Genetic ID is developing new proprietary methods that don't involve PCR or other kinds of amplification.
Experts predict that the next generation of GM crops with output traits will create even greater demand for testing. Instead of ensuring that GMOs are absent, food companies will want to verify that value-added traits are present.
"The long term trend will be more testing, particularly as output traits enter the market," says Envirologix's Layton. "Consumers will recognize the benefits of these traits and this will drive the demand for testing."
Contributing editor, Ken Roseboro, is a journalist who has written extensively about agricultural biotechnology issues. His work has appeared in a variety of business publications for the for seed, grain and food industries. Roseboro is president of Writing Solutions, Inc., a business communication firm in Iowa. He can be reached at: roseboro@kdsi.net.