Quantitative competitive PCR for the detection of genetically modified soybean and maize

 The surveillance of food labelling concerning genetically modified organisms (GMOs) requires DNA-based analytical techniques. Present assay systems allow the detection of GMO in food; however, they do not permit their quantitation. In this study, we report the development of quantitative competitive polymerase chain reaction (QC-PCR) systems for the detection and quantitation of the Roundup Ready soybean (RRS) and the Maximizer maize (MM) in food samples. Three DNA fragments that differ from the GMO-specific sequences by an insertion were constructed and used as internal standards in the PCR. These standards were calibrated by co-amplifying with mixtures containing RRS DNA and MM DNA, respectively. The calibrated QC-PCR systems were applied to nine commercial food samples containing RRS DNA and to three certified RRS flour mixtures in order to elucidate whether these food samples contain more or less than 1% RRS DNA. Finally, the GMO contents of four samples that were found to contain more than 1% RRS were determined by QC-PCR using various amounts of standard DNA. Received: 13 January 1998 / Revised version: 4 March 1998