Detection of genetically modified organisms in food:: critical points for duality assurance

The detection of genetically modified organisms (GMOs) by the polymerase chain reaction (PCR) is a complex multiparameter problem. Therefore, a number of critical issues in respect to quality control need to be considered. For practical purposes, the PCR process itself can be divided into three subprocesses: template isolation and reaction setup (pre-PCR), PCR reaction and detection of amplification products, and data evaluation (post-PCR). Crucial factors for the pre-PCR process are the following: homogeneity of the sample to be analysed, performance of template isolation and purification in terms of yield and purity, standardized process for the estimation of concentrations of genomic DNA and all reagents used in the reaction. For the PCR itself, crucial factors to be controlled are: setup of reactions, batch to batch variations of reagents, temperature-lime programs used for the PCR amplification, and the performance of different types of hardware (e.g. different brands of thermocyclers). The crucial factor for the post-PCR process is the detection of the amplification products of the PCR. The tremendous sensitivity of PCR methods requires a careful and consequent separation of the three processes in terms of hardware, laboratory space and sample handling. The avoidance of contamination is one of the most critical factors. The goal of quality assurance measures must be to ensure appropriate results at maximum sensitivity. The complexity of any PCR system used for the detection of GMOs leads to the requirement of a careful validation process for any laboratory using such methods. For qualitative analyses crucial validation parameters are: specificity, selectivity, repeatability, intermediate precision, reproducibility, limit of detection and robustness.