Evaluation and optimisation of five different extraction methods for soy DNA in chocolate and biscuits. Extraction of DNA as a first step in GMO analysis

A method is described to discriminate between genetically modified (GM) and non-modified foodstuffs by detecting the presence of newly introduced genes at the protein or DNA level. Currently available methods operate almost exclusively at the DNA level and are based on the polymerase chain reaction (PCR). The first and most crucial step in this process is the isolation of DNA. In this study, five different methods for the isolation of DNA from chocolate and biscuits were evaluated, using four commercially available extraction kits and a non-commercial method for amplification of the soybean-specific lectin gene. The latter method involves the use of hot-start Taq polymerase, to prevent the formation of non-specific amplification products, and an increase in the number of cycles from 35 to 41. The performance of the non-commercial cetyl trimethylammonium bromide (CTAB)-based method was the best, taking into consideration the adaptations of the extraction procedure, although this method was more time-consuming than the others. Chocolate (white, milk and dark) and several biscuits generated positive amplification results using this PCR approach. (C) 2004 Society of Chemical Industry.