Comparative evaluation of DNA extraction methods for detection of GMO in food

Extraction of DNA from the sample matrix is a critical step in the detection of transgenic DNA in food and feed. The extraction efficiency can be affected by several factors such as the degree of processing of the foodstuffs and the presence of PCR inhibitors in the food sample. The aim of this work was the comparative analysis of the following five commercial DNA extraction and purification methods: Wizard“ Minipreps DNA Purification Resin (Promega), Custom Magnetic DNA Purification Reagents (Promega), Generation TM Capture Column Kit (Gentra Systems), Puregene“ DNA Isolation Kit (Gentra Systems), Gene Elute Plant Genomic DNA Purification Kit (Sigma-Aldrich). DNA was isolated from simple (flours), complex ( feeds) and processed matrixes (bread, cakes and cookies) containing maize and/or soy among the ingredients. The quality and the concentration of the extracted DNA were determined spectrophotometrically while its suitability to PCR reaction was examined using a PCR system based on the amplification of two endogenous DNA sequences of maize and soy (zein and lectin, respectively). If amplifiable DNA was found, samples were then checked for the presence of the 35S promoter and of the cryia (Bt176 maize) and GTS (Roundup Ready soy) genes. As expected, the efficiency of DNA extraction was related to the type of matrix and to extraction method used. When compared for efficiency, the Wizard method showed the best results in terms of recovery and quality of DNA. Furthermore, by introducing some modifications to the standard procedure, the Wizard method allowed the recovery of amplifiable DNA also from highly processed food matrixes such as cookies and cakes. However, when the speed of the methods was compared, the Wizard method and the DNA Elution Kit (Gentra) showed the longest processing times. Finally, from a few processed matrixes (corn flakes and chocolate wafers) it was not possible to obtain DNA with any of the five tested methods