Limits of a PCR-based detection method for genetically modified soya beans in wheat bread production

The official PCR-based method for the detection of recombinant DNA from glyphosate-tolerant soya beans (GTS), laid down in the collection of methods according to Sect. 35 of the German Food Law, was investigated for applicability. As a model, wheat bread was produced with a 1% addition of baking aid consisting of 45% GTS flour. DNA extraction of samples drawn at various stages of the production process revealed that during the process a degradation of DNA took place, resulting in fragment sizes in bread of <500 bp. GTS DNA was detectable at all stages, al though the content of GTS flour in the dough and bread had dropped to only 0.4%. In 2 out of 15 commercial baking aids, GTS DNA was detected, reflecting the status of the use of GTS in that area. A model was also developed to study the effect on the detection of GTS under conditions when the target gene sequence of one primer is present in food originating from natural contamination or genetically modified organisms other than GTS. It was observed that high concentrations of competing DNA inhibited the PCR. This inhibition was overcome by increasing the concentration of Taq polymerase in the reaction mixture.