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H. PARKES, Laboratory of the Government Chemist, United Kingdom

Under current EU legislation, for a food ingredient to be exempt from labeling as GM, or to be labeled "GM-free", the retailer or supplier must be assured that it contains less than 1% GM protein or DNA. This "de minimis" threshold only applies to ingredients obtained from non-GM sources through audited identity preservation systems and recognizes the difficulties in guaranteeing complete segregation of non-GM crops as well as the opportunity for adventitious "contamination". Due diligence necessitates GM analysis to ensure compliance with the threshold level.

Various methods have been developed for the detection of genetically modified organisms. Protein based methods detect either the gene product or metabolites whose production is influenced by the gene product, but are limited by availability of specific antibodies and protein degradation on processing which generally limits the assay to raw foods. DNA based methods, are more reliable for the identification of genetic modifications, and can be applied to a greater range of food ingredients and products.

Two major analytical issues have come to the fore since GM food testing regimes have been introduced: · with what level of confidence can the current technology produce an accurate result? · are negative results too frequently obtained when analyzing some of the more processed, complex and composite GM positive foodstuffs?

To provide valid analytical data, techniques for GM detection must be specific, sensitive, reproducible and robust

The analytical challenges in the production of valid analytical data that accurately represents the GM status of a wide variety of raw and processed foodstuffs will be discussed.

Parkes, H.C. (1999) Food for thought. Chemistry in Britain. 35:32-34