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1.3 Detection methods

The new regulation on food stuffs ('Lebensmittelgesetzgebung') that became effective in Switzerland stipulates that all food stuffs, food additives and processing aids that are derived from or which contain GMOs require premarket approval (Article 15, LMV) and must be labelled as 'GVO-Erzeugnis' (GMO-product) according to Articles 22k and 23, 'Lebensmittelverordnung' (LMV). Products exempt from the labelling requirement need to be free of the GMO itself and must have been purified from the (transgenic) DNA (e.g. chemically defined substances like sugar). The novel food regulations under discussion within the EC commission will basically require labelling of GMO products if they are distinguishable from conventional products by scientific methods.

All GMOs that are used in food stuffs in the United Kingdom have to be approved by the ACNFP (Advisory Committee on Novel Foods and Processes). The British FAC (Food Advisory Committee) has developed a classification system that should be helpful in deciding whether labelling of a product is necessary or desirable (Atkins et al., 1992; Teuber, 1993):

• Nature-identical food products of genetically modified organisms: foods that are the product of, or which contain products of a GMO (but not the organism itself, its cells or DNA) and are identical to products from conventional organisms traditionally consumed (e.g. chymosin). The FAC concluded that labelling of chymosin or cheese produced with it is not required.
• Foods containing recombinant DNA which were produced by introducing genes only from the gene pool of its own species (self-cloning); e.g. bakers' and brewers' yeast that have been approved in the United Kingdom (Table 4, page 17). Again, the committee considered labelling not to be absolutely necessary, but recommended a case-by-case approach.
• Novel foods derived from GMOs but which contain neither the GMO itself nor its cells nor DNA and which differ from products conventionally consumed in Western Europe. Labelling of such products is recommended.
• Foods containing recombinant DNA (or the GMO or its cells) which were produced by introducing genes from the gene pool of a different species. Labelling of such products may be required, but the committee favoured a case-by-case examination.

The ongoing globalisation of trade is also affecting the food sector. It is plausible that genetically engineered crops approved only in foreign countries will make their way to the local market, especially when the respective country is a major producer of the crop. Current examples are the herbicide-tolerant soybean (Roundup Ready™, RR) from Monsanto and products from it or insect-resistant corn from CIBA-GEIGY that arrived in Switzerland and the EC, respectively, before approval of these products was granted (Butler, 1996). The soybean has by now been approved for food use in the United States, the European Community, Canada, the United Kingdom, the Netherlands, Japan, Switzerland, Mexico and Argentina. In the US, which is the main export country for soybeans worldwide, no special labelling of the genetically engineered soybean or products derived from it is required. Within the US for the year 1996, RR soybeans have mostly been processed indiscriminately from conventional soybean varieties. Some processing companies such as Central Soya Co. (Fort Wayne, Indiana) apparently intended to separate their products according to the soybean source (Wadman, 1996), but the bulk of the 1996 soybean harvest was not separated and may contain up to 1-2 % genetically modified soybeans.

The observed relative ease with which genetically modified products cross borders should be an added impetus for the EC and Swiss authorities to develop adequate methodology for identifying GMOs in food stuffs. This will facilitate controlling the adherence to the respective regulatory guidelines. Accurate labelling would also be an information service to consumers who want to exercise their freedom of choice in the market place. In the past months control authorities, trade and consumer organisations, as well as groups such as Greenpeace, have shown increasing interest in the development and increased availability of specific identification methods for GMO-products. A recently founded company in Iowa, USA provides analyses of predominantly raw, unprocessed food for approximately $ 450 per sample (Sept. 1996). It was reported that there has been tremendous interest in the analyses of the company (Wadman, 1996).

In contrast, there is only a very limited number of published detection methods designed to identify approved genetically modified food products such as the Flavr Savr™ tomato (Meyer, 1995a,b). Development of proper product identification methods is made difficult by the lack of specific information on the precise genetic changes differentiating genetically engineered products from their conventional counterparts. Therefore, it is not surprising that reviews published within the last few years mainly discuss theoretical aspects dealing with the identification of genetically engineered food products (Bähler, 1994; Schulze, 1994; Hammes and Hertel, 1995; Engel et al., 1995) or focus on the state-of-the-art in transgenic plant research (Niederhauser et al., 1996).

One central objective of this paper is to review published methods that have been designed for identifying genetically engineered foods and methods which may be relevant for the design of new methods. Information has been gathered from:

• Methods which have been (or soon will be) validated and published in official collections of methods for the identification of products in food derived from or consisting of GMOs.
• Methods which have been (or soon will be) published in scientific journals for the identification of food products consisting of or derived from GMOs.
• Publications in scientific journals describing the detection of GMOs (mostly microorganisms) in the environment.
• Articles in scientific journals describing the identification of DNA sequences or gene products that are also present as transgenes or respective translation products in approved GMOs.
• Publications from the area of food science (e.g. authenticity testing) containing information on the applicability of DNA-based methods for the analysis of processed foods.
• Methods for detection of pathogens in food; methods in clinical or veterinary diagnostics and other relevant areas.
• Highly specialised reports (e.g. annual reports from food control authorities) covering the detection of GMOs in food that are unavailable in common databases.
• Ongoing research projects concerning the detection or monitoring of GMOs.

The following compilation includes methods based on the detection of proteins as well as RNA- (NASBA) and DNA-based amplification techniques such as polymerase chain reaction (PCR), ligase chain reaction (LCR), Q-beta-replicase. The main focus is on DNA-based methods, in particular PCR, which represents the state-of-the-art technique for GMO detection in food. PCR combines high specificity with wide applicability with respect to the nature of the sample and suitability for laboratory diagnostics. Therefore, this report will also consider several articles dealing with specific problems which may arise when applying PCR for the analysis of food stuffs, and several approaches to prevent or counteract these problems.