Maize, the second most important genetically modified (GM) crop, has the highest number of authorised
GM events for food and feed in the EU. To provide consumer’s information, labelling for food products
containing more than 0.9% of GM material is demanded by the actual EU legislation. Analysis of foods is
then essential to detect and quantify GM maize material and verify the compliance with labelling information.
The aim of the present work was to assess the presence of GM maize in a range of processed
foods commercialised in Portugal between 2007 and 2010. For this purpose, screening of GM material
was carried out by qualitative PCR targeting the 35S promoter and the NOS terminator, followed by the
specific detection of Bt11, MON810, Bt176, GA21, MON863, NK603, TC1507 (also known as DAS1507),
DAS59122 and MIR604 events. The identified maize events were confirmed and quantified by real-time
PCR with hydrolysis probes. The overall results of GMO screening were 30% for 35S promoter, 10% for
NOS terminator and 25% for identified events. The most frequently detected events were MON810,
TC1507 and NK603, with one sample containing GA21, while the other events were not detected in any of
the analysed foods. The quantitative results suggest the need for a more severe control since 4% of the
analysed foods contained more than the threshold for labelling and none of them declared the presence
of GMO.
