The official method for the detection of genetically modified soybeans (German Food Act LMBG 35): a semi-quantitative study of sensitivity limits with glyphosate-tolerant soybeans (Roundup Ready) and insect-resistant Bt maize (Maximizer)

The aim of the study was to settle a concent for the standardised descripti on of the potency of a PCR setup with respect to the detection limit. The m ain terms used are the theoretical detection limit (L-theor) and the practi cal detection limit (L-prac). These detection limits were determined for th e example of two current PCR setups for the detection of genetically modifi ed soybeans and maize. The Ltheor for the detection of Roundup Ready soybea n DNA with the PCR setup applied was 0.005% genetically modified organism ( GMO)/non-GMO (w/w) (corresponding to 30 copies of the GMO soya genome per s ingle PCR reaction). In pre-mixed powder preparations (certified reference materials, CRMs) of soya it was possible to detect 0.1% GMO/non-GMO (w/w), i.e. this was the L-prac. The Ltheor for Bt maize was 0.005% GMO/non-GMO (w /w), that corresponded to 9 calculated genome copies per single reaction. W ithout background DNA, as few as 2 genome copies (0.01 ng GMO DNA) were cle arly detectable. As for soybeans, the L-prac of the available CRMs from tra nsgenic and conventional maize was 0.1% GMO/non-GMO (w/w). Quantitative sys tems for the investigation of foodstuffs are still not available as officia l methods, and are still being developed. Determining L-theor and L-prac va lues could be important for setting limits for the GMO contents of foods, w hen deciding whether they should be labelled. Concerning labelling limits, it is obvious that the PCR setups investigated have more sensitive detectio n thresholds than the limits under discussion for the labelling of foodstuf fs as "genetically modified".