Detection of four types of genetically modified maize by polymerase chain reaction and immuno-kit methods

To detect and identify four types of genetically modified (GM) maize, a polymerase chain reaction (PCR) assay and an immuno-assay kit were performed in this study. Primers specific to inserted genes in the Event 176 GM maize (Novartis company), Bt11 (Novartis company), MON810 (Monsanto company) and Liberty (AgrEvo company) were used to conduct the PCR assay. Four pairs of primers, namely, CDPK-cry (Event176), IV01-cry (Bt11), HS01-cry (MON810) and CM03-PA01 (Liberty) were used to identify the GM-maize. Results showed that the limit of detection for GM-maize were 0.01%, and 0.1%, and 1% (w/w) as using HS01-cry, CDPK-cry and IV01-cry, and CM03-PA01 primers, respectively. The GM-maize references as well as 20 food-grade maize samples were also tested using a commercial immuno-kit. Three GM-maize references, Event176, Bt11 and MON810, and 6 corn-middling pellet samples were tested as positives; while 14 popcorn samples were negative. To confirm these results, the 20 food-grade maize samples were further tested by the PCR method. Two types of GM-maize were detected in popcorn samples; while 3-4 types of GM-maize were detected in the samples of corn middling pellets. The results of this study demonstrate that using PCR method is capable of differentiating four types of GM-maize from non-GM products; while the commercial immuno-kit can only be used for screening purpose. All samples, with positive or negative results as tested by immuno-kit, need to be further confirmed by the PCR method. The results of this study also reveal that marketed maize products are usually mixed with different types of GM-maize.