New diagnostics track the identity of agricultural products.

The efforts of agricultural biotechnologists have resulted in commercial crops such as corn and soybean with new agronomic traits. This has been accomplished by taking novel pieces of DNA and inserting them into plants in a way that causes production of proteins that confer beneficial characteristics to the plant. The first wave of such crops all have traits that directly benefit farmers, including resistance to insects and herbicides. Genetically modified crops were introduced throughout the 1990s in the United States and have been rapidly adopted by the market segment they were intended to benefit, that is, the farmers. Indeed, in 1999, approximately half of the soybean and one-third of the corn crop in the United States was the product of agricultural biotechnology, and worldwide production of these crops is increasing rapidly (1).

Novel DNA and protein can be found to varying degrees in many parts of the modified plants, including seeds and grain, and the processed fractions and final foods prepared from them. While farmers in general have recognized the value of these first-generation agbiotech crops, consumers do not necessarily perceive a direct benefit to themselves. A general sense of anxiousness exists about any activity that could be viewed as “tampering” with the food supply. Especially in Europe, where there have been several scares related to the food supply in recent years, there is strong sentiment against the use of agbiotech crops for production of food and animal feed (2).

Companies developing agbiotech crops carry out extensive testing to demonstrate such things as safety and environmental impact, as well as agronomic performance, before commercialization. The data from these studies are reviewed by government authorities who must grant approval before the crop can be sold. Many such crops have already been granted approval for use in food and feed by governments all over the world. While there is general scientific consensus that foods derived from agbiotech crops do not pose human health concerns beyond those that are present in existing foods, loud voices within society, primarily consumer and environmental groups, have questioned whether the extent of testing is sufficient.

In addition to food safety concerns, many environmental groups have questioned whether the new genes inserted into these plants may find their way into other closely related plants and lead to unexpected and undesirable effects on the environment (3). Still other concerns have been raised about the effect that large-scale cultivation of a relatively limited number of varieties, representing a limited gene pool, may have on biological diversity throughout the world (4). The controversy surrounding agbiotech crops has left consumers confused and uncertain about the issues.

Laws for labeling
Many believe that if governments, scientists, industry, and consumer groups can’t come to a consensus regarding the overall safety of agbiotech, then consumers should be given the right to decide for themselves whether to eat foods containing agbiotech ingredients. As a result, several countries, including the European Union and Japan, have passed laws requiring that foods containing agbiotech ingredients be labeled as such.

An important aspect of these laws is the inclusion of a minimum threshold concentration. If a food contains agbiotech ingredients above the minimum threshold, the food needs to be labeled. Because the approved crops have already been determined to be safe for human consumption, the existence of a small percentage of an agbiotech ingredient below the threshold concentration has been determined to be an issue of commerce and international trade, rather than a safety issue.

For example, there is general recognition that when dealing with large containers filled with grain (elevators, barges, ships, etc.), it is impossible to prevent incidental commingling of the contents with material left in the container from the previous use. Existing international trade practices currently make allowances for incidental carryover between shipments. On the basis of similar considerations, food labeling laws incorporate the concept of a minimum threshold concentration. it is reasoned that foods that may contain agbiotech ingredients at concentrations less than the specified threshold, for example, because of incidental carryover during shipment, would not be labeled.

The explosive introduction and large-scale production of agbiotech crops, coupled with the adoption of food-labeling laws, have left farmers, grain import–export companies, food processors and retailers, and regulatory enforcement agencies scrambling to implement food labeling.

Identifying Crops
One way to know whether an ingredient is derived from an agbiotech crop is to establish the identity of the material at its origin and to trace its identity from planting through harvest, distribution, processing, and labeling in a way that preserves the identity of a product throughout the entire process. Current agricultural, distribution, and trade practices are not compatible with such a system. However, the entire industry recognizes that when the second wave of agbiotech products are commercialized—those containing traits valued by consumers (e.g., enhanced nutritional content)—identity-preservation systems will be necessary to tout and guarantee the added value of these crops. Industry, therefore, is already making plans to implement identity-preservation systems.

An alternative approach for determining whether a food contains ingredients derived from agbiotech crops is to check a representative sample for novel DNA or its resulting protein. The quantity of agbiotech crop in the food is then determined by extrapolation from the sample’s results. An inherent difficulty with this approach is that the analytical techniques measure protein or DNA, but the laws mandate labeling based on the percentage of genetically modified organisms (GMO) present in an ingredient. The definition of %GMO is crucial to determining concentrations and is operationally defined as the percentage of positive beans, kernels, seeds, or other discrete units present in a pool of non-GMO units. For example, 1 GMO soybean mixed with 99 non-GMO beans represents a 1% GMO. Europe has currently established a 1% GMO threshold with respect to food labeling, and Japan has established a 5% threshold.

To support labeling, a measurement technique must be able to determine whether the concentration of GMO in the sample is above or below the mandated threshold concentration with some specified level of confidence, accuracy, and precision. Techniques are available for detecting both proteins and nucleic acids, and their relative merits are the subject of considerable scientific debate (5, 6). It is possible to detect the novel DNA sequences present in agbiotech crops and ingredients using techniques such as the polymerase chain reaction (PCR). A PCR method for detecting the CP4 EPSPS gene, which confers resistance to the herbicide Roundup, was evaluated in a European Ring Study organized by the Joint Research Centre (JRC) of the European Union (7). The study findings demonstrated that the PCR method could detect the CP4 EPSPS gene, but only qualitatively. Thus, the method was not suitable for use in determining whether a sample contained GMO above or below a mandated threshold concentration.

Detection of CP4 EPSPS in the seeds of different crops.

Novel proteins can be detected in agbiotech crops and processed food fractions using immunoassays. Like PCR, an enzyme-linked immunosorbent assay (ELISA) that detects the CP4 EPSPS protein was also evaluated in a European Ring Study by the JRC (8). The test protocol was designed to determine themethod’s capability of distinguishing whether a sample contained GMO above or below an arbitrary threshold of 2%. The findings demonstrated that the samples identified as negative by the test contained less than 2% GMO, and samples that scored positive contained at least 0.85% GMO with a confidence of 99%. The within-laboratory repeatability was ±7%, and the reproducibility between laboratories was ±10%. Although the test was designed specifically to determine whether a sample was above or below a specified threshold, the data clearly demonstrated that the test could be used to determine GMO concentration quantitatively.

Realistic Tests
The utility of any testing method is ultimately limited by the nature of the specific application. Because of technical as well as practical considerations, food processors have not implemented large-scale testing programs to determine GMO concentrations in support of labeling. Instead, they have pushed the burden back on their raw material suppliers, the grain distribution system. Without question, the most critical point of monitoring in the grain distribution system is at the initial point of sale, that is, when the producer sells to the local elevator. As larger pools of grain are created, it becomes increasingly difficult and costly to acquire and analyze enough samples to get an accurate representation of the distribution of grain in a container.

The majority of grain is harvested during a frenzied period of time, typically two weeks, in which trucks are standing in line at elevators and moving through the system at a rate of about one every five minutes. Grain as a commodity cannot support much in the way of additional costs associated with testing. Under these conditions, it is critical to test grain immediately, on-site, at very low cost per sample, and the assay must be simple to use. Quantitative PCR is a highly complex procedure, requires expensive instrumentation and laboratory facilities, costs anywhere from $400 to $700 per sample, and routinely takes 3–10 days to get a result. Although ELISA methods require only one to four hours to perform and cost one-tenth as much, they still are not ideal for truck-side testing.

Another form of immunoassay, the immunochromatographic strip test, has been developed to meet the performance specifications required for testing agbiotech crops in the field (see box, “Strip Tests” for AgBiotech Proteins). These tests use the same technology as the home pregnancy test. They are very easy to use, cost less than $10 per test, take 5–10 minutes to complete, and can be performed truck-side.

For the foreseeable future, agbiotech crops will coexist with conventional varieties, and the world will have to find ways to deal with both. Coupling the advent of agbiotech crops with consumer-valued traits will necessitate that systems and strategies capable of preserving the identity of these crops be in place to capture the added value; work that is done now to develop these systems will facilitate commercialization in the future. Although detection technology is available for most agbiotech crops, implementation of testing lags behind production and regulations, leaving the entire industry in a quandary on how to proceed. In the near term, it seems likely that solutions will comprise elements of identity preservation, incorporating screening tests at critical control points throughout the distribution system along with limited, standardized testing at major points of export and import

References

1. James, C. ISAAA Briefs, 1999, 12.
2. Longman, P. J. et al. U.S. News and World Report 1999, 12 7(4), 38.
3. Mann, C. Technol. Rev. 1999, 102 (4), 36–38.
4. A Conventional Argument: Arranging the Biosafety Protocol” The Economist January 29, 2000, p 95.
5. Meeting of the International Life Sciences Institute, Brussels, Belgium, June 3–5, 1998.
6. Biotechnology Detection Methods Validation Workshop, sponsored by U.S. Department of Agriculture (Grain Inspection, Packers, and Stockyards Administration) and the Analytical Environmental Immunochemical Consortium, Kansas City, MO, February 24–25, 2000.
7. Lipp, M. et al. J. of AOAC International 1999, 82 (4), 923.
8. Lipp, M. et al. J. of AOAC International 2000, 83 (4), in press.

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James W. Stave is vice president of research and development for Strategic Diagnostics Inc. (Newark, DE). Donald Durandetta is a product manager for agricultural products for Strategic Diagnostics Inc. (Newark, DE). Comments and questions for the author can be addressed to the Editorial Officeby e-mail at tcaw@acs.org, by fax at 202-776-8166 or by post at 1155 16th Street, NW; Washington, DC 20036.

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Copyright © 2000 American Chemical Society.