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S. J. FRITSCHEL, Marketing, Qualicon Inc., Rte 141 & Henry Clay Rds, Wilmington, DE 19880-0357

The introduction of genetically modified crops such as soy beans has created a demand for tests that can quantify the amount of modified product in crops and foods. Qualicon, a DuPont Subsidiary, has developed an assay for quantifying the genetically modified content of soy protein. The assay is applicable to other food types. Qualicon’s service laboratory provides this analysis to customers in the United States and Europe and soon in Asia. The closed-tube homogeneous PCR process uses Qualicon’s BAX^® detection system and DNA intercalating dye, SYBR Green-I. During each thermal cycle, fluorescence data is collected at an intermediate temperature between the extension and denaturation steps. As the specific PCR product is generated, the dye intercalates into the product and the total fluorescence signal increases. Because there is no detectable product during the early stages of PCR, the signal during this period becomes a baseline fluorescence value. Regression analysis of the fluorescence increase determines the cycle at which the increase exceeds 5% of the baseline fluorescence. This becomes the threshold cycle (C_T). Standards with known levels of genetically modified DNA (0.5%-5.0%) are amplified and the fluorescence signal recorded after each cycle. A curve is generated based on the linear regression fit of C_T versus the log of percent genetically modified material. Unknown sample C_T values are plotted against the standard curve and a genetically modified percentage is determined. Using a similar technique, the amount of total soy DNA can be quantified by targeting an amplification reaction to the lectin coding region of soybean DNA. The ratio of the amount of the modified insert to the total amount of soy DNA allows an accurate percentage of genetically modified material to be calculated. The assay can be targeted to screen for genetic modification in other food types as required.