Validation of a method based on polymerase chain reaction for the detection of genetically modified organisms in various processed foodstuffs

A qualitative screening method was validated for the detection of genetical ly modified organisms (GMOs) in various processed food matrices (cooked mai ze grit, infant formula, biscuits, meal of acidified soybeans). The prepare d food matrices contained each 0%, 2%, 100% (10% instead of 100% in the cas e of biscuits) of Roundup-Ready(R) soybeans and/or of Bt-176 maize. The met hod was based on the detection of the introduced DNA sequences by using the polymerase chain reaction (PCR) for amplification of DNA. Two different de tection systems were applied: one based on the 35S promoter fragment which is present in GM-soybeans and in GM-maize and one based on the nos terminat or sequence which is present only in GM-soybeans. Prior to the validation s tudy, it was demonstrated that the food matrices were homogenous and that t here was no cross-contamination between GMO-containing and GMO-free samples . Some laboratories had a high portion of false positive results probably d ue to laboratory contamination whereas all others reported nearly always co rrect data for all matrices investigated. Statistical analysis showed that after exclusion of the outliers, an average of 97% correct results was obta ined for non-GMO containing samples (3% false positive results) and an aver age of 98% correct results for GMO-containing samples (2% false negative re sults). The validated method was shown to be suitable for screening of CMOs in processed food matrices also when extreme physical stress was applied ( e.g., heating for 45 min at 100 degreesC or 10 min at 180 degreesC) or when multiple components were present, as in the case of biscuit preparations.