Semi-Quantification of GM Maize Using Ready-To-Use RTi-PCR Plates

European Union (EU) legislation foresees that food and feed are labelled for their genetically modified organism (GMO) content when the ingredients contain authorised GMOs in a proportion higher than 0.9 %. Non-authorised GMOs are not allowed on the EU market. Exception is made for feed materials containing traces of GM events lawfully placed on the market in non-EU countries and for which an authorisation is pending in the EU or expired: in these cases, a minimum required performance limit (MRPL) of 0.1 % is applied. Considering that the number of GMOs placed on the EU market is constantly growing, laboratories need to expand their capacity accordingly to be able to identify and, if necessary, quantify any GM material. To this purpose, our laboratory had previously developed a multi-target ready-to-use system, also known as a pre-spotted plate (PSP), which allows the qualitative detection of up to 44 GM events in one single real-time (RTi) PCR experiment. Should any event be detected, the laboratory would proceed with its quantification. This study evaluates the possibility to use the data generated by the PSP system in a semi-quantitative manner, allowing a categorisation of the GM quantity in the sample. ΔCq values were calculated and modelled via linear regression to estimate limits indicating whether the GM content is (1) above, (2) below or (3) near a defined quantity and thus requires further quantification. Identifying the GM events present in a sample and simultaneously discriminating whether it needs or not further quantification would offer to testing laboratories a valuable gain in time and resources. Six maize GM events frequently found in food and feed were selected for this evaluation (Bt11, MON810, MON88017, MON89034, NK603 and TC1507). The feasibility of the approach was successfully verified in-house using spiked and proficiency test samples.