Applicability of ELISA Testing

[ ELISA Testing Introduction ]

ELISA assays are faster and less expensive than PCR analysis. Training technicians to perform these tests is relatively quick and easy. The investment in equipment is much less than for PCR, especially quantitative PCR. However, there are several disadvantages that limit the applicability of ELISA testing for genetically engineered products.

The chief disadvantage, especially for a food processing company, is that the target proteins are denatured relatively easily during processing. Therefore, for a processed food or ingredient, the target protein epitope may not be present in the condition detectable by the antibodies.

The second drawback to using an ELISA test is that commercial kits are available for only a few of the genetically engineered agricultural products now being grown. Also, at this time, each kit can only detect one protein; so, if, as in corn, there is more than one possible modification or if more than one species of plant material is present, then a series of ELISA tests would be necessary, assuming a kit was available for each of the proteins in question. In real world applications, for multi-event crops such as corn, ELISA on raw ingredients is used as a risk management tool rather then as a method to detect all possible GM events.

There are also questions related to the quantification capabilities of ELISA tests. Test results are reported in ug/ml of target protein to test solution. A conversion is then made to percent of genetically modified material present. However, it has been shown that the amount of protein expressed in genetically engineered corn varies from field to field, year to year and between varieties. So the exact correlation of amount of protein to amount of bioengineered crop present is not precise. Further, in one corn event, Bt176 (approximately 1% of 1999 plantings), the novel protein is primarily expressed in the green leaf and minimally in the kernel.

Keypoints of ELISA Testing

• Faster and less expensive than PCR.

• Can detect only one GMO at a time. (Future kits may be able to "stack" several together)

• Sensitivity will vary with the specific kit, some as sensitive as PCR (down to 0.1%)

• Only a few kits commercially available at this time (RUR Soybean, Starlink and Bt Corn)

• Best used for raw agricultural or slightly processed products as processing will denature proteins

• ELISA technique is widely accepted and used in many other applications, such as with pathogens and mycotoxins

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