Determination of unprocessed genetically modified soybean in foods using simplex and duplex real‐time PCR with an internal standard

Summary We developed a method using an internal standard to determine the amount of unprocessed genetically modified organisms (GMO) in foods as GMO weight per weight of total food (w/w tf ) using real‐time PCR. Food samples were spiked with an internal standard, a ColE1 plasmid, and DNA was extracted from the samples using a silica membrane‐type kit and analysed using real‐time PCR. The relationship between the GMO amount and the copy number ratio of the transgene to ColE1 in 0.1–5% w/w tf GM soybean powders was found to have a correlation coefficient ( r ) of 0.97. GMO was quantified in food samples spiked with GM soybean (final amount 0.5% w/w tf GMO). The average GMO amount ranged from 0.35% to 0.63% w/w tf . The results show that our method should be useful for quantifying unprocessed GMO in foods. We also developed a duplex assay, which is simpler and more accurate than the simplex assay.