The second most dominant genetically modified (GM) crop is maize. Increasing number of GM maize events puts significant pressure on GMO testing laboratories to achieve the level of competence necessary to fulfill legal requirements. In the European Union, Polymerase Chain Reaction (PCR) is the method of choice for identification and quantification of GMOs. We performed verification of validated methods for identification of four GM maize events. Additionaly we aimed to explore the option of designing a method for simultaneous detection of these events in a multiplex PCR reaction. DNA was extracted from certified reference materials (CRM) using validated CTAB extraction protocol. Concentration of DNA was measured using Qubit dsDNA Broad Range Assay. Amplification of taxon specific marker for maize and all event-specific methods was performed according to the JRC Compendium of Reference Methods for GMO Analysis. Absolute limit of detection (LODabs) was determined for taxon specific and four event specific RealTime PCR based methods. DNA extracted from CRMs showed sufficient concentration for downstream analyses and preparation of dilutions for determination of LODabs. Determined LODabs for all tested methods meet acceptance criteria. As expected, the methods performance with respect to the repeatability and precision decline with the decrease in concentration of the target. Event-specific GA21 and NK603 methods show high Ct values at the determined LODabs. However, by adjusting the concentrations of primers and probes sensitivity of these two methods should be improved. Considering that the amplicons for all five methods are quite short (<120 bp) optimization of multiplex reaction conditions for simultaneous amplification should be feasible

Soy sauce is worldwide popular condiment of Asian origin. With the advent of GM soybean production, soy sauce drew the interest of food safety control. Samples collected for inspection are generally of industrial grade soy sauce type, which is produced from hydrolyzed soybean and grain. Following the failure to perform RealTime PCR based GMO screening on a number of submitted samples we tested our screening system on soy sauce produced following traditional method based on fermentation. Four batches of soy sauce were produced and DNA extracted. DNA concentration ranged from 32,68 to 65,36 ng/μl. Amplification of taxon specific target was successful with rather high Ct ( > 30). Promoter P-35S sequence was not detected, but T-NOS was detected in three samples with values reaching or exceeding LOD of the method. The results show that it is possible to detect transgenic elements in traditionally produced soy sauce while DNA extraction from industrial grade soy sauce is not possible.